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<div class="section" id="module-ssl">
<span id="ssl-tls-ssl-wrapper-for-socket-objects"></span><h1>17.3. <a class="reference internal" href="#module-ssl" title="ssl: TLS/SSL wrapper for socket objects"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ssl</span></code></a> — TLS/SSL wrapper for socket objects<a class="headerlink" href="#module-ssl" title="Permalink to this headline">¶</a></h1>
<span class="target" id="index-0"></span><div class="versionadded" id="index-1">
<p><span class="versionmodified added">New in version 2.6.</span></p>
</div>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/2.7/Lib/ssl.py">Lib/ssl.py</a></p>
<hr class="docutils" />
<p>This module provides access to Transport Layer Security (often known as “Secure
Sockets Layer”) encryption and peer authentication facilities for network
sockets, both client-side and server-side. This module uses the OpenSSL
library. It is available on all modern Unix systems, Windows, Mac OS X, and
probably additional platforms, as long as OpenSSL is installed on that platform.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.13: </span>Updated to support linking with OpenSSL 1.1.0</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Some behavior may be platform dependent, since calls are made to the
operating system socket APIs. The installed version of OpenSSL may also
cause variations in behavior. For example, TLSv1.1 and TLSv1.2 come with
openssl version 1.0.1.</p>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Don’t use this module without reading the <a class="reference internal" href="#ssl-security"><span class="std std-ref">Security considerations</span></a>. Doing so
may lead to a false sense of security, as the default settings of the
ssl module are not necessarily appropriate for your application.</p>
</div>
<p>This section documents the objects and functions in the <code class="docutils literal notranslate"><span class="pre">ssl</span></code> module; for more
general information about TLS, SSL, and certificates, the reader is referred to
the documents in the “See Also” section at the bottom.</p>
<p>This module provides a class, <code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLSocket</span></code>, which is derived from the
<a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate"><span class="pre">socket.socket</span></code></a> type, and provides a socket-like wrapper that also
encrypts and decrypts the data going over the socket with SSL. It supports
additional methods such as <code class="xref py py-meth docutils literal notranslate"><span class="pre">getpeercert()</span></code>, which retrieves the
certificate of the other side of the connection, and <code class="xref py py-meth docutils literal notranslate"><span class="pre">cipher()</span></code>,which
retrieves the cipher being used for the secure connection.</p>
<p>For more sophisticated applications, the <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLContext</span></code></a> class
helps manage settings and certificates, which can then be inherited
by SSL sockets created through the <a class="reference internal" href="#ssl.SSLContext.wrap_socket" title="ssl.SSLContext.wrap_socket"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.wrap_socket()</span></code></a> method.</p>
<div class="section" id="functions-constants-and-exceptions">
<h2>17.3.1. Functions, Constants, and Exceptions<a class="headerlink" href="#functions-constants-and-exceptions" title="Permalink to this headline">¶</a></h2>
<dl class="exception">
<dt id="ssl.SSLError">
<em class="property">exception </em><code class="descclassname">ssl.</code><code class="descname">SSLError</code><a class="headerlink" href="#ssl.SSLError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised to signal an error from the underlying SSL implementation (currently
provided by the OpenSSL library). This signifies some problem in the
higher-level encryption and authentication layer that’s superimposed on the
underlying network connection. This error is a subtype of
<a class="reference internal" href="socket.html#socket.error" title="socket.error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">socket.error</span></code></a>, which in turn is a subtype of <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a>. The
error code and message of <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a> instances are provided by the
OpenSSL library.</p>
<dl class="attribute">
<dt id="ssl.SSLError.library">
<code class="descname">library</code><a class="headerlink" href="#ssl.SSLError.library" title="Permalink to this definition">¶</a></dt>
<dd><p>A string mnemonic designating the OpenSSL submodule in which the error
occurred, such as <code class="docutils literal notranslate"><span class="pre">SSL</span></code>, <code class="docutils literal notranslate"><span class="pre">PEM</span></code> or <code class="docutils literal notranslate"><span class="pre">X509</span></code>. The range of possible
values depends on the OpenSSL version.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="ssl.SSLError.reason">
<code class="descname">reason</code><a class="headerlink" href="#ssl.SSLError.reason" title="Permalink to this definition">¶</a></dt>
<dd><p>A string mnemonic designating the reason this error occurred, for
example <code class="docutils literal notranslate"><span class="pre">CERTIFICATE_VERIFY_FAILED</span></code>. The range of possible
values depends on the OpenSSL version.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
</dd></dl>
<dl class="exception">
<dt id="ssl.SSLZeroReturnError">
<em class="property">exception </em><code class="descclassname">ssl.</code><code class="descname">SSLZeroReturnError</code><a class="headerlink" href="#ssl.SSLZeroReturnError" title="Permalink to this definition">¶</a></dt>
<dd><p>A subclass of <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a> raised when trying to read or write and
the SSL connection has been closed cleanly. Note that this doesn’t
mean that the underlying transport (read TCP) has been closed.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="ssl.SSLWantReadError">
<em class="property">exception </em><code class="descclassname">ssl.</code><code class="descname">SSLWantReadError</code><a class="headerlink" href="#ssl.SSLWantReadError" title="Permalink to this definition">¶</a></dt>
<dd><p>A subclass of <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a> raised by a <a class="reference internal" href="#ssl-nonblocking"><span class="std std-ref">non-blocking SSL socket</span></a> when trying to read or write data, but more data needs
to be received on the underlying TCP transport before the request can be
fulfilled.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="ssl.SSLWantWriteError">
<em class="property">exception </em><code class="descclassname">ssl.</code><code class="descname">SSLWantWriteError</code><a class="headerlink" href="#ssl.SSLWantWriteError" title="Permalink to this definition">¶</a></dt>
<dd><p>A subclass of <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a> raised by a <a class="reference internal" href="#ssl-nonblocking"><span class="std std-ref">non-blocking SSL socket</span></a> when trying to read or write data, but more data needs
to be sent on the underlying TCP transport before the request can be
fulfilled.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="ssl.SSLSyscallError">
<em class="property">exception </em><code class="descclassname">ssl.</code><code class="descname">SSLSyscallError</code><a class="headerlink" href="#ssl.SSLSyscallError" title="Permalink to this definition">¶</a></dt>
<dd><p>A subclass of <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a> raised when a system error was encountered
while trying to fulfill an operation on a SSL socket. Unfortunately,
there is no easy way to inspect the original errno number.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="ssl.SSLEOFError">
<em class="property">exception </em><code class="descclassname">ssl.</code><code class="descname">SSLEOFError</code><a class="headerlink" href="#ssl.SSLEOFError" title="Permalink to this definition">¶</a></dt>
<dd><p>A subclass of <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a> raised when the SSL connection has been
terminated abruptly. Generally, you shouldn’t try to reuse the underlying
transport when this error is encountered.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="ssl.CertificateError">
<em class="property">exception </em><code class="descclassname">ssl.</code><code class="descname">CertificateError</code><a class="headerlink" href="#ssl.CertificateError" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised to signal an error with a certificate (such as mismatching
hostname). Certificate errors detected by OpenSSL, though, raise
an <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a>.</p>
</dd></dl>
<div class="section" id="socket-creation">
<h3>17.3.1.1. Socket creation<a class="headerlink" href="#socket-creation" title="Permalink to this headline">¶</a></h3>
<p>The following function allows for standalone socket creation. Starting from
Python 2.7.9, it can be more flexible to use <a class="reference internal" href="#ssl.SSLContext.wrap_socket" title="ssl.SSLContext.wrap_socket"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.wrap_socket()</span></code></a>
instead.</p>
<dl class="function">
<dt id="ssl.wrap_socket">
<code class="descclassname">ssl.</code><code class="descname">wrap_socket</code><span class="sig-paren">(</span><em>sock</em>, <em>keyfile=None</em>, <em>certfile=None</em>, <em>server_side=False</em>, <em>cert_reqs=CERT_NONE</em>, <em>ssl_version={see docs}</em>, <em>ca_certs=None</em>, <em>do_handshake_on_connect=True</em>, <em>suppress_ragged_eofs=True</em>, <em>ciphers=None</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.wrap_socket" title="Permalink to this definition">¶</a></dt>
<dd><p>Takes an instance <code class="docutils literal notranslate"><span class="pre">sock</span></code> of <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate"><span class="pre">socket.socket</span></code></a>, and returns an instance
of <code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLSocket</span></code>, a subtype of <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate"><span class="pre">socket.socket</span></code></a>, which wraps
the underlying socket in an SSL context. <code class="docutils literal notranslate"><span class="pre">sock</span></code> must be a
<a class="reference internal" href="socket.html#socket.SOCK_STREAM" title="socket.SOCK_STREAM"><code class="xref py py-data docutils literal notranslate"><span class="pre">SOCK_STREAM</span></code></a> socket; other socket types are unsupported.</p>
<p>For client-side sockets, the context construction is lazy; if the
underlying socket isn’t connected yet, the context construction will be
performed after <code class="xref py py-meth docutils literal notranslate"><span class="pre">connect()</span></code> is called on the socket. For
server-side sockets, if the socket has no remote peer, it is assumed
to be a listening socket, and the server-side SSL wrapping is
automatically performed on client connections accepted via the
<code class="xref py py-meth docutils literal notranslate"><span class="pre">accept()</span></code> method. <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a> may raise <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a>.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">keyfile</span></code> and <code class="docutils literal notranslate"><span class="pre">certfile</span></code> parameters specify optional files which
contain a certificate to be used to identify the local side of the
connection. See the discussion of <a class="reference internal" href="#ssl-certificates"><span class="std std-ref">Certificates</span></a> for more
information on how the certificate is stored in the <code class="docutils literal notranslate"><span class="pre">certfile</span></code>.</p>
<p>The parameter <code class="docutils literal notranslate"><span class="pre">server_side</span></code> is a boolean which identifies whether
server-side or client-side behavior is desired from this socket.</p>
<p>The parameter <code class="docutils literal notranslate"><span class="pre">cert_reqs</span></code> specifies whether a certificate is required from
the other side of the connection, and whether it will be validated if
provided. It must be one of the three values <a class="reference internal" href="#ssl.CERT_NONE" title="ssl.CERT_NONE"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_NONE</span></code></a>
(certificates ignored), <a class="reference internal" href="#ssl.CERT_OPTIONAL" title="ssl.CERT_OPTIONAL"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_OPTIONAL</span></code></a> (not required, but validated
if provided), or <a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a> (required and validated). If the
value of this parameter is not <a class="reference internal" href="#ssl.CERT_NONE" title="ssl.CERT_NONE"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_NONE</span></code></a>, then the <code class="docutils literal notranslate"><span class="pre">ca_certs</span></code>
parameter must point to a file of CA certificates.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">ca_certs</span></code> file contains a set of concatenated “certification
authority” certificates, which are used to validate certificates passed from
the other end of the connection. See the discussion of
<a class="reference internal" href="#ssl-certificates"><span class="std std-ref">Certificates</span></a> for more information about how to arrange the
certificates in this file.</p>
<p>The parameter <code class="docutils literal notranslate"><span class="pre">ssl_version</span></code> specifies which version of the SSL protocol to
use. Typically, the server chooses a particular protocol version, and the
client must adapt to the server’s choice. Most of the versions are not
interoperable with the other versions. If not specified, the default is
<a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a>; it provides the most compatibility with other
versions.</p>
<p>Here’s a table showing which versions in a client (down the side) can connect
to which versions in a server (along the top):</p>
<blockquote>
<div><table class="docutils align-center">
<colgroup>
<col style="width: 29%" />
<col style="width: 11%" />
<col style="width: 11%" />
<col style="width: 12%" />
<col style="width: 11%" />
<col style="width: 13%" />
<col style="width: 13%" />
</colgroup>
<tbody>
<tr class="row-odd"><td><p><em>client</em> / <strong>server</strong></p></td>
<td><p><strong>SSLv2</strong></p></td>
<td><p><strong>SSLv3</strong></p></td>
<td><p><strong>SSLv23</strong></p></td>
<td><p><strong>TLSv1</strong></p></td>
<td><p><strong>TLSv1.1</strong></p></td>
<td><p><strong>TLSv1.2</strong></p></td>
</tr>
<tr class="row-even"><td><p><em>SSLv2</em></p></td>
<td><p>yes</p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
<td><p>no</p></td>
<td><p>no</p></td>
<td><p>no</p></td>
</tr>
<tr class="row-odd"><td><p><em>SSLv3</em></p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
<td><p>yes</p></td>
<td><p>no</p></td>
<td><p>no</p></td>
<td><p>no</p></td>
</tr>
<tr class="row-even"><td><p><em>SSLv23</em> <a class="footnote-reference brackets" href="#id2" id="id1">1</a></p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
<td><p>yes</p></td>
<td><p>yes</p></td>
<td><p>yes</p></td>
<td><p>yes</p></td>
</tr>
<tr class="row-odd"><td><p><em>TLSv1</em></p></td>
<td><p>no</p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
<td><p>yes</p></td>
<td><p>no</p></td>
<td><p>no</p></td>
</tr>
<tr class="row-even"><td><p><em>TLSv1.1</em></p></td>
<td><p>no</p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
<td><p>no</p></td>
</tr>
<tr class="row-odd"><td><p><em>TLSv1.2</em></p></td>
<td><p>no</p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
<td><p>no</p></td>
<td><p>no</p></td>
<td><p>yes</p></td>
</tr>
</tbody>
</table>
</div></blockquote>
<p class="rubric">Footnotes</p>
<dl class="footnote brackets">
<dt class="label" id="id2"><span class="brackets"><a class="fn-backref" href="#id1">1</a></span></dt>
<dd><p>TLS 1.3 protocol will be available with <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a> in
OpenSSL >= 1.1.1. There is no dedicated PROTOCOL constant for just
TLS 1.3.</p>
</dd>
</dl>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Which connections succeed will vary depending on the version of
OpenSSL. For example, before OpenSSL 1.0.0, an SSLv23 client
would always attempt SSLv2 connections.</p>
</div>
<p>The <em>ciphers</em> parameter sets the available ciphers for this SSL object.
It should be a string in the <a class="reference external" href="https://www.openssl.org/docs/manmaster/man1/ciphers.html">OpenSSL cipher list format</a>.</p>
<p>The parameter <code class="docutils literal notranslate"><span class="pre">do_handshake_on_connect</span></code> specifies whether to do the SSL
handshake automatically after doing a <code class="xref py py-meth docutils literal notranslate"><span class="pre">socket.connect()</span></code>, or whether the
application program will call it explicitly, by invoking the
<a class="reference internal" href="#ssl.SSLSocket.do_handshake" title="ssl.SSLSocket.do_handshake"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.do_handshake()</span></code></a> method. Calling
<a class="reference internal" href="#ssl.SSLSocket.do_handshake" title="ssl.SSLSocket.do_handshake"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.do_handshake()</span></code></a> explicitly gives the program control over the
blocking behavior of the socket I/O involved in the handshake.</p>
<p>The parameter <code class="docutils literal notranslate"><span class="pre">suppress_ragged_eofs</span></code> specifies how the
<code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.read()</span></code> method should signal unexpected EOF from the other end
of the connection. If specified as <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a> (the default), it returns a
normal EOF (an empty bytes object) in response to unexpected EOF errors
raised from the underlying socket; if <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a>, it will raise the
exceptions back to the caller.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7: </span>New optional argument <em>ciphers</em>.</p>
</div>
</dd></dl>
</div>
<div class="section" id="context-creation">
<h3>17.3.1.2. Context creation<a class="headerlink" href="#context-creation" title="Permalink to this headline">¶</a></h3>
<p>A convenience function helps create <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> objects for common
purposes.</p>
<dl class="function">
<dt id="ssl.create_default_context">
<code class="descclassname">ssl.</code><code class="descname">create_default_context</code><span class="sig-paren">(</span><em>purpose=Purpose.SERVER_AUTH</em>, <em>cafile=None</em>, <em>capath=None</em>, <em>cadata=None</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.create_default_context" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a new <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> object with default settings for
the given <em>purpose</em>. The settings are chosen by the <a class="reference internal" href="#module-ssl" title="ssl: TLS/SSL wrapper for socket objects"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ssl</span></code></a> module,
and usually represent a higher security level than when calling the
<a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> constructor directly.</p>
<p><em>cafile</em>, <em>capath</em>, <em>cadata</em> represent optional CA certificates to
trust for certificate verification, as in
<a class="reference internal" href="#ssl.SSLContext.load_verify_locations" title="ssl.SSLContext.load_verify_locations"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_verify_locations()</span></code></a>. If all three are
<a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>, this function can choose to trust the system’s default
CA certificates instead.</p>
<p>The settings are: <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a>, <a class="reference internal" href="#ssl.OP_NO_SSLv2" title="ssl.OP_NO_SSLv2"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_SSLv2</span></code></a>, and
<a class="reference internal" href="#ssl.OP_NO_SSLv3" title="ssl.OP_NO_SSLv3"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_SSLv3</span></code></a> with high encryption cipher suites without RC4 and
without unauthenticated cipher suites. Passing <a class="reference internal" href="#ssl.Purpose.SERVER_AUTH" title="ssl.Purpose.SERVER_AUTH"><code class="xref py py-data docutils literal notranslate"><span class="pre">SERVER_AUTH</span></code></a>
as <em>purpose</em> sets <a class="reference internal" href="#ssl.SSLContext.verify_mode" title="ssl.SSLContext.verify_mode"><code class="xref py py-data docutils literal notranslate"><span class="pre">verify_mode</span></code></a> to <a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-data docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a>
and either loads CA certificates (when at least one of <em>cafile</em>, <em>capath</em> or
<em>cadata</em> is given) or uses <a class="reference internal" href="#ssl.SSLContext.load_default_certs" title="ssl.SSLContext.load_default_certs"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_default_certs()</span></code></a> to load
default CA certificates.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The protocol, options, cipher and other settings may change to more
restrictive values anytime without prior deprecation. The values
represent a fair balance between compatibility and security.</p>
<p>If your application needs specific settings, you should create a
<a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> and apply the settings yourself.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>If you find that when certain older clients or servers attempt to connect
with a <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> created by this function that they get an error
stating “Protocol or cipher suite mismatch”, it may be that they only
support SSL3.0 which this function excludes using the
<a class="reference internal" href="#ssl.OP_NO_SSLv3" title="ssl.OP_NO_SSLv3"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_SSLv3</span></code></a>. SSL3.0 is widely considered to be <a class="reference external" href="https://en.wikipedia.org/wiki/POODLE">completely broken</a>. If you still wish to continue to
use this function but still allow SSL 3.0 connections you can re-enable
them using:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">ctx</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">create_default_context</span><span class="p">(</span><span class="n">Purpose</span><span class="o">.</span><span class="n">CLIENT_AUTH</span><span class="p">)</span>
<span class="n">ctx</span><span class="o">.</span><span class="n">options</span> <span class="o">&=</span> <span class="o">~</span><span class="n">ssl</span><span class="o">.</span><span class="n">OP_NO_SSLv3</span>
</pre></div>
</div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.10: </span>RC4 was dropped from the default cipher string.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.13: </span>ChaCha20/Poly1305 was added to the default cipher string.</p>
<p>3DES was dropped from the default cipher string.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="ssl._https_verify_certificates">
<code class="descclassname">ssl.</code><code class="descname">_https_verify_certificates</code><span class="sig-paren">(</span><em>enable=True</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl._https_verify_certificates" title="Permalink to this definition">¶</a></dt>
<dd><p>Specifies whether or not server certificates are verified when creating
client HTTPS connections without specifying a particular SSL context.</p>
<p>Starting with Python 2.7.9, <a class="reference internal" href="httplib.html#module-httplib" title="httplib: HTTP and HTTPS protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">httplib</span></code></a> and modules which use it, such as
<a class="reference internal" href="urllib2.html#module-urllib2" title="urllib2: Next generation URL opening library."><code class="xref py py-mod docutils literal notranslate"><span class="pre">urllib2</span></code></a> and <a class="reference internal" href="xmlrpclib.html#module-xmlrpclib" title="xmlrpclib: XML-RPC client access."><code class="xref py py-mod docutils literal notranslate"><span class="pre">xmlrpclib</span></code></a>, default to verifying remote server
certificates received when establishing client HTTPS connections. This
default verification checks that the certificate is signed by a Certificate
Authority in the system trust store and that the Common Name (or Subject
Alternate Name) on the presented certificate matches the requested host.</p>
<p>Setting <em>enable</em> to <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a> ensures this default behaviour is in
effect.</p>
<p>Setting <em>enable</em> to <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a> reverts the default HTTPS certificate
handling to that of Python 2.7.8 and earlier, allowing connections to
servers using self-signed certificates, servers using certificates signed
by a Certicate Authority not present in the system trust store, and servers
where the hostname does not match the presented server certificate.</p>
<p>The leading underscore on this function denotes that it intentionally does
not exist in any implementation of Python 3 and may not be present in all
Python 2.7 implementations. The portable approach to bypassing certificate
checks or the system trust store when necessary is for tools to enable that
on a case-by-case basis by explicitly passing in a suitably configured SSL
context, rather than reverting the default behaviour of the standard library
client modules.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.12.</span></p>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<ul class="simple">
<li><p><a class="reference external" href="http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-9365">CVE-2014-9365</a>
– HTTPS man-in-the-middle attack against Python clients using default settings</p></li>
<li><p><span class="target" id="index-2"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0476"><strong>PEP 476</strong></a> – Enabling certificate verification by default for HTTPS</p></li>
<li><p><span class="target" id="index-3"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0493"><strong>PEP 493</strong></a> – HTTPS verification migration tools for Python 2.7</p></li>
</ul>
</div>
</dd></dl>
</div>
<div class="section" id="random-generation">
<h3>17.3.1.3. Random generation<a class="headerlink" href="#random-generation" title="Permalink to this headline">¶</a></h3>
<blockquote>
<div><div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7.13: </span>OpenSSL has deprecated <code class="xref py py-func docutils literal notranslate"><span class="pre">ssl.RAND_pseudo_bytes()</span></code>, use
<code class="xref py py-func docutils literal notranslate"><span class="pre">ssl.RAND_bytes()</span></code> instead.</p>
</div>
</div></blockquote>
<dl class="function">
<dt id="ssl.RAND_status">
<code class="descclassname">ssl.</code><code class="descname">RAND_status</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.RAND_status" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the SSL pseudo-random number generator has been seeded
with ‘enough’ randomness, and <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise. You can use
<a class="reference internal" href="#ssl.RAND_egd" title="ssl.RAND_egd"><code class="xref py py-func docutils literal notranslate"><span class="pre">ssl.RAND_egd()</span></code></a> and <a class="reference internal" href="#ssl.RAND_add" title="ssl.RAND_add"><code class="xref py py-func docutils literal notranslate"><span class="pre">ssl.RAND_add()</span></code></a> to increase the randomness of
the pseudo-random number generator.</p>
</dd></dl>
<dl class="function">
<dt id="ssl.RAND_egd">
<code class="descclassname">ssl.</code><code class="descname">RAND_egd</code><span class="sig-paren">(</span><em>path</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.RAND_egd" title="Permalink to this definition">¶</a></dt>
<dd><p>If you are running an entropy-gathering daemon (EGD) somewhere, and <em>path</em>
is the pathname of a socket connection open to it, this will read 256 bytes
of randomness from the socket, and add it to the SSL pseudo-random number
generator to increase the security of generated secret keys. This is
typically only necessary on systems without better sources of randomness.</p>
<p>See <a class="reference external" href="http://egd.sourceforge.net/">http://egd.sourceforge.net/</a> or <a class="reference external" href="http://prngd.sourceforge.net/">http://prngd.sourceforge.net/</a> for sources
of entropy-gathering daemons.</p>
<p>Availability: not available with LibreSSL and OpenSSL > 1.1.0</p>
</dd></dl>
<dl class="function">
<dt id="ssl.RAND_add">
<code class="descclassname">ssl.</code><code class="descname">RAND_add</code><span class="sig-paren">(</span><em>bytes</em>, <em>entropy</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.RAND_add" title="Permalink to this definition">¶</a></dt>
<dd><p>Mix the given <em>bytes</em> into the SSL pseudo-random number generator. The
parameter <em>entropy</em> (a float) is a lower bound on the entropy contained in
string (so you can always use <code class="xref py py-const docutils literal notranslate"><span class="pre">0.0</span></code>). See <span class="target" id="index-4"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc1750.html"><strong>RFC 1750</strong></a> for more
information on sources of entropy.</p>
</dd></dl>
</div>
<div class="section" id="certificate-handling">
<h3>17.3.1.4. Certificate handling<a class="headerlink" href="#certificate-handling" title="Permalink to this headline">¶</a></h3>
<dl class="function">
<dt id="ssl.match_hostname">
<code class="descclassname">ssl.</code><code class="descname">match_hostname</code><span class="sig-paren">(</span><em>cert</em>, <em>hostname</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.match_hostname" title="Permalink to this definition">¶</a></dt>
<dd><p>Verify that <em>cert</em> (in decoded format as returned by
<a class="reference internal" href="#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.getpeercert()</span></code></a>) matches the given <em>hostname</em>. The rules
applied are those for checking the identity of HTTPS servers as outlined
in <span class="target" id="index-5"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2818.html"><strong>RFC 2818</strong></a> and <span class="target" id="index-6"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc6125.html"><strong>RFC 6125</strong></a>, except that IP addresses are not currently
supported. In addition to HTTPS, this function should be suitable for
checking the identity of servers in various SSL-based protocols such as
FTPS, IMAPS, POPS and others.</p>
<p><a class="reference internal" href="#ssl.CertificateError" title="ssl.CertificateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CertificateError</span></code></a> is raised on failure. On success, the function
returns nothing:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">cert</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'subject'</span><span class="p">:</span> <span class="p">(((</span><span class="s1">'commonName'</span><span class="p">,</span> <span class="s1">'example.com'</span><span class="p">),),)}</span>
<span class="gp">>>> </span><span class="n">ssl</span><span class="o">.</span><span class="n">match_hostname</span><span class="p">(</span><span class="n">cert</span><span class="p">,</span> <span class="s2">"example.com"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">ssl</span><span class="o">.</span><span class="n">match_hostname</span><span class="p">(</span><span class="n">cert</span><span class="p">,</span> <span class="s2">"example.org"</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
File <span class="nb">"<stdin>"</span>, line <span class="m">1</span>, in <span class="n"><module></span>
File <span class="nb">"/home/py3k/Lib/ssl.py"</span>, line <span class="m">130</span>, in <span class="n">match_hostname</span>
<span class="gr">ssl.CertificateError</span>: <span class="n">hostname 'example.org' doesn't match 'example.com'</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="ssl.cert_time_to_seconds">
<code class="descclassname">ssl.</code><code class="descname">cert_time_to_seconds</code><span class="sig-paren">(</span><em>cert_time</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.cert_time_to_seconds" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the time in seconds since the Epoch, given the <code class="docutils literal notranslate"><span class="pre">cert_time</span></code>
string representing the “notBefore” or “notAfter” date from a
certificate in <code class="docutils literal notranslate"><span class="pre">"%b</span> <span class="pre">%d</span> <span class="pre">%H:%M:%S</span> <span class="pre">%Y</span> <span class="pre">%Z"</span></code> strptime format (C
locale).</p>
<p>Here’s an example:</p>
<div class="highlight-pycon3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">ssl</span>
<span class="gp">>>> </span><span class="n">timestamp</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">cert_time_to_seconds</span><span class="p">(</span><span class="s2">"Jan 5 09:34:43 2018 GMT"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">timestamp</span>
<span class="go">1515144883</span>
<span class="gp">>>> </span><span class="kn">from</span> <span class="nn">datetime</span> <span class="k">import</span> <span class="n">datetime</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">datetime</span><span class="o">.</span><span class="n">utcfromtimestamp</span><span class="p">(</span><span class="n">timestamp</span><span class="p">))</span>
<span class="go">2018-01-05 09:34:43</span>
</pre></div>
</div>
<p>“notBefore” or “notAfter” dates must use GMT (<span class="target" id="index-7"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5280.html"><strong>RFC 5280</strong></a>).</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.9: </span>Interpret the input time as a time in UTC as specified by ‘GMT’
timezone in the input string. Local timezone was used
previously. Return an integer (no fractions of a second in the
input format)</p>
</div>
</dd></dl>
<dl class="function">
<dt id="ssl.get_server_certificate">
<code class="descclassname">ssl.</code><code class="descname">get_server_certificate</code><span class="sig-paren">(</span><em>addr</em>, <em>ssl_version=PROTOCOL_SSLv23</em>, <em>ca_certs=None</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.get_server_certificate" title="Permalink to this definition">¶</a></dt>
<dd><p>Given the address <code class="docutils literal notranslate"><span class="pre">addr</span></code> of an SSL-protected server, as a (<em>hostname</em>,
<em>port-number</em>) pair, fetches the server’s certificate, and returns it as a
PEM-encoded string. If <code class="docutils literal notranslate"><span class="pre">ssl_version</span></code> is specified, uses that version of
the SSL protocol to attempt to connect to the server. If <code class="docutils literal notranslate"><span class="pre">ca_certs</span></code> is
specified, it should be a file containing a list of root certificates, the
same format as used for the same parameter in <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a>. The call
will attempt to validate the server certificate against that set of root
certificates, and will fail if the validation attempt fails.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.9: </span>This function is now IPv6-compatible, and the default <em>ssl_version</em> is
changed from <a class="reference internal" href="#ssl.PROTOCOL_SSLv3" title="ssl.PROTOCOL_SSLv3"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv3</span></code></a> to <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a> for
maximum compatibility with modern servers.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="ssl.DER_cert_to_PEM_cert">
<code class="descclassname">ssl.</code><code class="descname">DER_cert_to_PEM_cert</code><span class="sig-paren">(</span><em>DER_cert_bytes</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.DER_cert_to_PEM_cert" title="Permalink to this definition">¶</a></dt>
<dd><p>Given a certificate as a DER-encoded blob of bytes, returns a PEM-encoded
string version of the same certificate.</p>
</dd></dl>
<dl class="function">
<dt id="ssl.PEM_cert_to_DER_cert">
<code class="descclassname">ssl.</code><code class="descname">PEM_cert_to_DER_cert</code><span class="sig-paren">(</span><em>PEM_cert_string</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.PEM_cert_to_DER_cert" title="Permalink to this definition">¶</a></dt>
<dd><p>Given a certificate as an ASCII PEM string, returns a DER-encoded sequence of
bytes for that same certificate.</p>
</dd></dl>
<dl class="function">
<dt id="ssl.get_default_verify_paths">
<code class="descclassname">ssl.</code><code class="descname">get_default_verify_paths</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.get_default_verify_paths" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns a named tuple with paths to OpenSSL’s default cafile and capath.
The paths are the same as used by
<a class="reference internal" href="#ssl.SSLContext.set_default_verify_paths" title="ssl.SSLContext.set_default_verify_paths"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_default_verify_paths()</span></code></a>. The return value is a
<a class="reference internal" href="../glossary.html#term-named-tuple"><span class="xref std std-term">named tuple</span></a> <code class="docutils literal notranslate"><span class="pre">DefaultVerifyPaths</span></code>:</p>
<ul class="simple">
<li><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">cafile</span></code> - resolved path to cafile or <code class="docutils literal notranslate"><span class="pre">None</span></code> if the file doesn’t exist,</p></li>
<li><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">capath</span></code> - resolved path to capath or <code class="docutils literal notranslate"><span class="pre">None</span></code> if the directory doesn’t exist,</p></li>
<li><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">openssl_cafile_env</span></code> - OpenSSL’s environment key that points to a cafile,</p></li>
<li><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">openssl_cafile</span></code> - hard coded path to a cafile,</p></li>
<li><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">openssl_capath_env</span></code> - OpenSSL’s environment key that points to a capath,</p></li>
<li><p><code class="xref py py-attr docutils literal notranslate"><span class="pre">openssl_capath</span></code> - hard coded path to a capath directory</p></li>
</ul>
<p>Availability: LibreSSL ignores the environment vars
<code class="xref py py-attr docutils literal notranslate"><span class="pre">openssl_cafile_env</span></code> and <code class="xref py py-attr docutils literal notranslate"><span class="pre">openssl_capath_env</span></code></p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="ssl.enum_certificates">
<code class="descclassname">ssl.</code><code class="descname">enum_certificates</code><span class="sig-paren">(</span><em>store_name</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.enum_certificates" title="Permalink to this definition">¶</a></dt>
<dd><p>Retrieve certificates from Windows’ system cert store. <em>store_name</em> may be
one of <code class="docutils literal notranslate"><span class="pre">CA</span></code>, <code class="docutils literal notranslate"><span class="pre">ROOT</span></code> or <code class="docutils literal notranslate"><span class="pre">MY</span></code>. Windows may provide additional cert
stores, too.</p>
<p>The function returns a list of (cert_bytes, encoding_type, trust) tuples.
The encoding_type specifies the encoding of cert_bytes. It is either
<code class="xref py py-const docutils literal notranslate"><span class="pre">x509_asn</span></code> for X.509 ASN.1 data or <code class="xref py py-const docutils literal notranslate"><span class="pre">pkcs_7_asn</span></code> for
PKCS#7 ASN.1 data. Trust specifies the purpose of the certificate as a set
of OIDS or exactly <code class="docutils literal notranslate"><span class="pre">True</span></code> if the certificate is trustworthy for all
purposes.</p>
<p>Example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">ssl</span><span class="o">.</span><span class="n">enum_certificates</span><span class="p">(</span><span class="s2">"CA"</span><span class="p">)</span>
<span class="go">[(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}),</span>
<span class="go"> (b'data...', 'x509_asn', True)]</span>
</pre></div>
</div>
<p>Availability: Windows.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="ssl.enum_crls">
<code class="descclassname">ssl.</code><code class="descname">enum_crls</code><span class="sig-paren">(</span><em>store_name</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.enum_crls" title="Permalink to this definition">¶</a></dt>
<dd><p>Retrieve CRLs from Windows’ system cert store. <em>store_name</em> may be
one of <code class="docutils literal notranslate"><span class="pre">CA</span></code>, <code class="docutils literal notranslate"><span class="pre">ROOT</span></code> or <code class="docutils literal notranslate"><span class="pre">MY</span></code>. Windows may provide additional cert
stores, too.</p>
<p>The function returns a list of (cert_bytes, encoding_type, trust) tuples.
The encoding_type specifies the encoding of cert_bytes. It is either
<code class="xref py py-const docutils literal notranslate"><span class="pre">x509_asn</span></code> for X.509 ASN.1 data or <code class="xref py py-const docutils literal notranslate"><span class="pre">pkcs_7_asn</span></code> for
PKCS#7 ASN.1 data.</p>
<p>Availability: Windows.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
</div>
<div class="section" id="constants">
<h3>17.3.1.5. Constants<a class="headerlink" href="#constants" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="ssl.CERT_NONE">
<code class="descclassname">ssl.</code><code class="descname">CERT_NONE</code><a class="headerlink" href="#ssl.CERT_NONE" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_mode" title="ssl.SSLContext.verify_mode"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_mode</span></code></a>, or the <code class="docutils literal notranslate"><span class="pre">cert_reqs</span></code>
parameter to <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a>. In this mode (the default), no
certificates will be required from the other side of the socket connection.
If a certificate is received from the other end, no attempt to validate it
is made.</p>
<p>See the discussion of <a class="reference internal" href="#ssl-security"><span class="std std-ref">Security considerations</span></a> below.</p>
</dd></dl>
<dl class="data">
<dt id="ssl.CERT_OPTIONAL">
<code class="descclassname">ssl.</code><code class="descname">CERT_OPTIONAL</code><a class="headerlink" href="#ssl.CERT_OPTIONAL" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_mode" title="ssl.SSLContext.verify_mode"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_mode</span></code></a>, or the <code class="docutils literal notranslate"><span class="pre">cert_reqs</span></code>
parameter to <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a>. In this mode no certificates will be
required from the other side of the socket connection; but if they
are provided, validation will be attempted and an <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLError</span></code></a>
will be raised on failure.</p>
<p>Use of this setting requires a valid set of CA certificates to
be passed, either to <a class="reference internal" href="#ssl.SSLContext.load_verify_locations" title="ssl.SSLContext.load_verify_locations"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_verify_locations()</span></code></a> or as a
value of the <code class="docutils literal notranslate"><span class="pre">ca_certs</span></code> parameter to <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a>.</p>
</dd></dl>
<dl class="data">
<dt id="ssl.CERT_REQUIRED">
<code class="descclassname">ssl.</code><code class="descname">CERT_REQUIRED</code><a class="headerlink" href="#ssl.CERT_REQUIRED" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_mode" title="ssl.SSLContext.verify_mode"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_mode</span></code></a>, or the <code class="docutils literal notranslate"><span class="pre">cert_reqs</span></code>
parameter to <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a>. In this mode, certificates are
required from the other side of the socket connection; an <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLError</span></code></a>
will be raised if no certificate is provided, or if its validation fails.</p>
<p>Use of this setting requires a valid set of CA certificates to
be passed, either to <a class="reference internal" href="#ssl.SSLContext.load_verify_locations" title="ssl.SSLContext.load_verify_locations"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_verify_locations()</span></code></a> or as a
value of the <code class="docutils literal notranslate"><span class="pre">ca_certs</span></code> parameter to <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a>.</p>
</dd></dl>
<dl class="data">
<dt id="ssl.VERIFY_DEFAULT">
<code class="descclassname">ssl.</code><code class="descname">VERIFY_DEFAULT</code><a class="headerlink" href="#ssl.VERIFY_DEFAULT" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_flags" title="ssl.SSLContext.verify_flags"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_flags</span></code></a>. In this mode, certificate
revocation lists (CRLs) are not checked. By default OpenSSL does neither
require nor verify CRLs.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.VERIFY_CRL_CHECK_LEAF">
<code class="descclassname">ssl.</code><code class="descname">VERIFY_CRL_CHECK_LEAF</code><a class="headerlink" href="#ssl.VERIFY_CRL_CHECK_LEAF" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_flags" title="ssl.SSLContext.verify_flags"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_flags</span></code></a>. In this mode, only the
peer cert is check but non of the intermediate CA certificates. The mode
requires a valid CRL that is signed by the peer cert’s issuer (its direct
ancestor CA). If no proper has been loaded
<a class="reference internal" href="#ssl.SSLContext.load_verify_locations" title="ssl.SSLContext.load_verify_locations"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.load_verify_locations</span></code></a>, validation will fail.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.VERIFY_CRL_CHECK_CHAIN">
<code class="descclassname">ssl.</code><code class="descname">VERIFY_CRL_CHECK_CHAIN</code><a class="headerlink" href="#ssl.VERIFY_CRL_CHECK_CHAIN" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_flags" title="ssl.SSLContext.verify_flags"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_flags</span></code></a>. In this mode, CRLs of
all certificates in the peer cert chain are checked.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.VERIFY_X509_STRICT">
<code class="descclassname">ssl.</code><code class="descname">VERIFY_X509_STRICT</code><a class="headerlink" href="#ssl.VERIFY_X509_STRICT" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_flags" title="ssl.SSLContext.verify_flags"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_flags</span></code></a> to disable workarounds
for broken X.509 certificates.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.VERIFY_X509_TRUSTED_FIRST">
<code class="descclassname">ssl.</code><code class="descname">VERIFY_X509_TRUSTED_FIRST</code><a class="headerlink" href="#ssl.VERIFY_X509_TRUSTED_FIRST" title="Permalink to this definition">¶</a></dt>
<dd><p>Possible value for <a class="reference internal" href="#ssl.SSLContext.verify_flags" title="ssl.SSLContext.verify_flags"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_flags</span></code></a>. It instructs OpenSSL to
prefer trusted certificates when building the trust chain to validate a
certificate. This flag is enabled by default.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.10.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.PROTOCOL_TLS">
<code class="descclassname">ssl.</code><code class="descname">PROTOCOL_TLS</code><a class="headerlink" href="#ssl.PROTOCOL_TLS" title="Permalink to this definition">¶</a></dt>
<dd><p>Selects the highest protocol version that both the client and server support.
Despite the name, this option can select “TLS” protocols as well as “SSL”.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.13.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.PROTOCOL_SSLv23">
<code class="descclassname">ssl.</code><code class="descname">PROTOCOL_SSLv23</code><a class="headerlink" href="#ssl.PROTOCOL_SSLv23" title="Permalink to this definition">¶</a></dt>
<dd><p>Alias for <code class="docutils literal notranslate"><span class="pre">PROTOCOL_TLS</span></code>.</p>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7.13: </span>Use <code class="docutils literal notranslate"><span class="pre">PROTOCOL_TLS</span></code> instead.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.PROTOCOL_SSLv2">
<code class="descclassname">ssl.</code><code class="descname">PROTOCOL_SSLv2</code><a class="headerlink" href="#ssl.PROTOCOL_SSLv2" title="Permalink to this definition">¶</a></dt>
<dd><p>Selects SSL version 2 as the channel encryption protocol.</p>
<p>This protocol is not available if OpenSSL is compiled with the
<code class="docutils literal notranslate"><span class="pre">OPENSSL_NO_SSL2</span></code> flag.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>SSL version 2 is insecure. Its use is highly discouraged.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7.13: </span>OpenSSL has removed support for SSLv2.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.PROTOCOL_SSLv3">
<code class="descclassname">ssl.</code><code class="descname">PROTOCOL_SSLv3</code><a class="headerlink" href="#ssl.PROTOCOL_SSLv3" title="Permalink to this definition">¶</a></dt>
<dd><p>Selects SSL version 3 as the channel encryption protocol.</p>
<p>This protocol is not be available if OpenSSL is compiled with the
<code class="docutils literal notranslate"><span class="pre">OPENSSL_NO_SSLv3</span></code> flag.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>SSL version 3 is insecure. Its use is highly discouraged.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7.13: </span>OpenSSL has deprecated all version specific protocols. Use the default
protocol with flags like <code class="docutils literal notranslate"><span class="pre">OP_NO_SSLv3</span></code> instead.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.PROTOCOL_TLSv1">
<code class="descclassname">ssl.</code><code class="descname">PROTOCOL_TLSv1</code><a class="headerlink" href="#ssl.PROTOCOL_TLSv1" title="Permalink to this definition">¶</a></dt>
<dd><p>Selects TLS version 1.0 as the channel encryption protocol.</p>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7.13: </span>OpenSSL has deprecated all version specific protocols. Use the default
protocol with flags like <code class="docutils literal notranslate"><span class="pre">OP_NO_SSLv3</span></code> instead.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.PROTOCOL_TLSv1_1">
<code class="descclassname">ssl.</code><code class="descname">PROTOCOL_TLSv1_1</code><a class="headerlink" href="#ssl.PROTOCOL_TLSv1_1" title="Permalink to this definition">¶</a></dt>
<dd><p>Selects TLS version 1.1 as the channel encryption protocol.
Available only with openssl version 1.0.1+.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7.13: </span>OpenSSL has deprecated all version specific protocols. Use the default
protocol with flags like <code class="docutils literal notranslate"><span class="pre">OP_NO_SSLv3</span></code> instead.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.PROTOCOL_TLSv1_2">
<code class="descclassname">ssl.</code><code class="descname">PROTOCOL_TLSv1_2</code><a class="headerlink" href="#ssl.PROTOCOL_TLSv1_2" title="Permalink to this definition">¶</a></dt>
<dd><p>Selects TLS version 1.2 as the channel encryption protocol. This is the
most modern version, and probably the best choice for maximum protection,
if both sides can speak it. Available only with openssl version 1.0.1+.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 2.7.13: </span>OpenSSL has deprecated all version specific protocols. Use the default
protocol with flags like <code class="docutils literal notranslate"><span class="pre">OP_NO_SSLv3</span></code> instead.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_ALL">
<code class="descclassname">ssl.</code><code class="descname">OP_ALL</code><a class="headerlink" href="#ssl.OP_ALL" title="Permalink to this definition">¶</a></dt>
<dd><p>Enables workarounds for various bugs present in other SSL implementations.
This option is set by default. It does not necessarily set the same
flags as OpenSSL’s <code class="docutils literal notranslate"><span class="pre">SSL_OP_ALL</span></code> constant.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_NO_SSLv2">
<code class="descclassname">ssl.</code><code class="descname">OP_NO_SSLv2</code><a class="headerlink" href="#ssl.OP_NO_SSLv2" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents an SSLv2 connection. This option is only applicable in
conjunction with <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-const docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a>. It prevents the peers from
choosing SSLv2 as the protocol version.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_NO_SSLv3">
<code class="descclassname">ssl.</code><code class="descname">OP_NO_SSLv3</code><a class="headerlink" href="#ssl.OP_NO_SSLv3" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents an SSLv3 connection. This option is only applicable in
conjunction with <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-const docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a>. It prevents the peers from
choosing SSLv3 as the protocol version.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_NO_TLSv1">
<code class="descclassname">ssl.</code><code class="descname">OP_NO_TLSv1</code><a class="headerlink" href="#ssl.OP_NO_TLSv1" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents a TLSv1 connection. This option is only applicable in
conjunction with <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-const docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a>. It prevents the peers from
choosing TLSv1 as the protocol version.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_NO_TLSv1_1">
<code class="descclassname">ssl.</code><code class="descname">OP_NO_TLSv1_1</code><a class="headerlink" href="#ssl.OP_NO_TLSv1_1" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents a TLSv1.1 connection. This option is only applicable in conjunction
with <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-const docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a>. It prevents the peers from choosing TLSv1.1 as
the protocol version. Available only with openssl version 1.0.1+.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_NO_TLSv1_2">
<code class="descclassname">ssl.</code><code class="descname">OP_NO_TLSv1_2</code><a class="headerlink" href="#ssl.OP_NO_TLSv1_2" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents a TLSv1.2 connection. This option is only applicable in conjunction
with <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-const docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a>. It prevents the peers from choosing TLSv1.2 as
the protocol version. Available only with openssl version 1.0.1+.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_NO_TLSv1_3">
<code class="descclassname">ssl.</code><code class="descname">OP_NO_TLSv1_3</code><a class="headerlink" href="#ssl.OP_NO_TLSv1_3" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents a TLSv1.3 connection. This option is only applicable in conjunction
with <a class="reference internal" href="#ssl.PROTOCOL_TLS" title="ssl.PROTOCOL_TLS"><code class="xref py py-const docutils literal notranslate"><span class="pre">PROTOCOL_TLS</span></code></a>. It prevents the peers from choosing TLSv1.3 as
the protocol version. TLS 1.3 is available with OpenSSL 1.1.1 or later.
When Python has been compiled against an older version of OpenSSL, the
flag defaults to <em>0</em>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.15.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_CIPHER_SERVER_PREFERENCE">
<code class="descclassname">ssl.</code><code class="descname">OP_CIPHER_SERVER_PREFERENCE</code><a class="headerlink" href="#ssl.OP_CIPHER_SERVER_PREFERENCE" title="Permalink to this definition">¶</a></dt>
<dd><p>Use the server’s cipher ordering preference, rather than the client’s.
This option has no effect on client sockets and SSLv2 server sockets.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_SINGLE_DH_USE">
<code class="descclassname">ssl.</code><code class="descname">OP_SINGLE_DH_USE</code><a class="headerlink" href="#ssl.OP_SINGLE_DH_USE" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents re-use of the same DH key for distinct SSL sessions. This
improves forward secrecy but requires more computational resources.
This option only applies to server sockets.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_SINGLE_ECDH_USE">
<code class="descclassname">ssl.</code><code class="descname">OP_SINGLE_ECDH_USE</code><a class="headerlink" href="#ssl.OP_SINGLE_ECDH_USE" title="Permalink to this definition">¶</a></dt>
<dd><p>Prevents re-use of the same ECDH key for distinct SSL sessions. This
improves forward secrecy but requires more computational resources.
This option only applies to server sockets.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_ENABLE_MIDDLEBOX_COMPAT">
<code class="descclassname">ssl.</code><code class="descname">OP_ENABLE_MIDDLEBOX_COMPAT</code><a class="headerlink" href="#ssl.OP_ENABLE_MIDDLEBOX_COMPAT" title="Permalink to this definition">¶</a></dt>
<dd><p>Send dummy Change Cipher Spec (CCS) messages in TLS 1.3 handshake to make
a TLS 1.3 connection look more like a TLS 1.2 connection.</p>
<p>This option is only available with OpenSSL 1.1.1 and later.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.16.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OP_NO_COMPRESSION">
<code class="descclassname">ssl.</code><code class="descname">OP_NO_COMPRESSION</code><a class="headerlink" href="#ssl.OP_NO_COMPRESSION" title="Permalink to this definition">¶</a></dt>
<dd><p>Disable compression on the SSL channel. This is useful if the application
protocol supports its own compression scheme.</p>
<p>This option is only available with OpenSSL 1.0.0 and later.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.HAS_ALPN">
<code class="descclassname">ssl.</code><code class="descname">HAS_ALPN</code><a class="headerlink" href="#ssl.HAS_ALPN" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether the OpenSSL library has built-in support for the <em>Application-Layer
Protocol Negotiation</em> TLS extension as described in <span class="target" id="index-8"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc7301.html"><strong>RFC 7301</strong></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.10.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.HAS_ECDH">
<code class="descclassname">ssl.</code><code class="descname">HAS_ECDH</code><a class="headerlink" href="#ssl.HAS_ECDH" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether the OpenSSL library has built-in support for Elliptic Curve-based
Diffie-Hellman key exchange. This should be true unless the feature was
explicitly disabled by the distributor.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.HAS_SNI">
<code class="descclassname">ssl.</code><code class="descname">HAS_SNI</code><a class="headerlink" href="#ssl.HAS_SNI" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether the OpenSSL library has built-in support for the <em>Server Name
Indication</em> extension (as defined in <span class="target" id="index-9"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc4366.html"><strong>RFC 4366</strong></a>).</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.HAS_NPN">
<code class="descclassname">ssl.</code><code class="descname">HAS_NPN</code><a class="headerlink" href="#ssl.HAS_NPN" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether the OpenSSL library has built-in support for <em>Next Protocol
Negotiation</em> as described in the <a class="reference external" href="https://tools.ietf.org/html/draft-agl-tls-nextprotoneg">NPN draft specification</a>. When true,
you can use the <a class="reference internal" href="#ssl.SSLContext.set_npn_protocols" title="ssl.SSLContext.set_npn_protocols"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_npn_protocols()</span></code></a> method to advertise
which protocols you want to support.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.HAS_TLSv1_3">
<code class="descclassname">ssl.</code><code class="descname">HAS_TLSv1_3</code><a class="headerlink" href="#ssl.HAS_TLSv1_3" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether the OpenSSL library has built-in support for the TLS 1.3 protocol.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.15.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.CHANNEL_BINDING_TYPES">
<code class="descclassname">ssl.</code><code class="descname">CHANNEL_BINDING_TYPES</code><a class="headerlink" href="#ssl.CHANNEL_BINDING_TYPES" title="Permalink to this definition">¶</a></dt>
<dd><p>List of supported TLS channel binding types. Strings in this list
can be used as arguments to <a class="reference internal" href="#ssl.SSLSocket.get_channel_binding" title="ssl.SSLSocket.get_channel_binding"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.get_channel_binding()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OPENSSL_VERSION">
<code class="descclassname">ssl.</code><code class="descname">OPENSSL_VERSION</code><a class="headerlink" href="#ssl.OPENSSL_VERSION" title="Permalink to this definition">¶</a></dt>
<dd><p>The version string of the OpenSSL library loaded by the interpreter:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">ssl</span><span class="o">.</span><span class="n">OPENSSL_VERSION</span>
<span class="go">'OpenSSL 0.9.8k 25 Mar 2009'</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OPENSSL_VERSION_INFO">
<code class="descclassname">ssl.</code><code class="descname">OPENSSL_VERSION_INFO</code><a class="headerlink" href="#ssl.OPENSSL_VERSION_INFO" title="Permalink to this definition">¶</a></dt>
<dd><p>A tuple of five integers representing version information about the
OpenSSL library:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">ssl</span><span class="o">.</span><span class="n">OPENSSL_VERSION_INFO</span>
<span class="go">(0, 9, 8, 11, 15)</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.OPENSSL_VERSION_NUMBER">
<code class="descclassname">ssl.</code><code class="descname">OPENSSL_VERSION_NUMBER</code><a class="headerlink" href="#ssl.OPENSSL_VERSION_NUMBER" title="Permalink to this definition">¶</a></dt>
<dd><p>The raw version number of the OpenSSL library, as a single integer:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">ssl</span><span class="o">.</span><span class="n">OPENSSL_VERSION_NUMBER</span>
<span class="go">9470143L</span>
<span class="gp">>>> </span><span class="nb">hex</span><span class="p">(</span><span class="n">ssl</span><span class="o">.</span><span class="n">OPENSSL_VERSION_NUMBER</span><span class="p">)</span>
<span class="go">'0x9080bfL'</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.ALERT_DESCRIPTION_HANDSHAKE_FAILURE">
<code class="descclassname">ssl.</code><code class="descname">ALERT_DESCRIPTION_HANDSHAKE_FAILURE</code><a class="headerlink" href="#ssl.ALERT_DESCRIPTION_HANDSHAKE_FAILURE" title="Permalink to this definition">¶</a></dt>
<dt id="ssl.ALERT_DESCRIPTION_INTERNAL_ERROR">
<code class="descclassname">ssl.</code><code class="descname">ALERT_DESCRIPTION_INTERNAL_ERROR</code><a class="headerlink" href="#ssl.ALERT_DESCRIPTION_INTERNAL_ERROR" title="Permalink to this definition">¶</a></dt>
<dt>
<code class="descname">ALERT_DESCRIPTION_*</code></dt>
<dd><p>Alert Descriptions from <span class="target" id="index-10"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5246.html"><strong>RFC 5246</strong></a> and others. The <a class="reference external" href="https://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-6">IANA TLS Alert Registry</a>
contains this list and references to the RFCs where their meaning is defined.</p>
<p>Used as the return value of the callback function in
<a class="reference internal" href="#ssl.SSLContext.set_servername_callback" title="ssl.SSLContext.set_servername_callback"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_servername_callback()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.Purpose.SERVER_AUTH">
<code class="descclassname">Purpose.</code><code class="descname">SERVER_AUTH</code><a class="headerlink" href="#ssl.Purpose.SERVER_AUTH" title="Permalink to this definition">¶</a></dt>
<dd><p>Option for <a class="reference internal" href="#ssl.create_default_context" title="ssl.create_default_context"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_default_context()</span></code></a> and
<a class="reference internal" href="#ssl.SSLContext.load_default_certs" title="ssl.SSLContext.load_default_certs"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_default_certs()</span></code></a>. This value indicates that the
context may be used to authenticate Web servers (therefore, it will
be used to create client-side sockets).</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="ssl.Purpose.CLIENT_AUTH">
<code class="descclassname">Purpose.</code><code class="descname">CLIENT_AUTH</code><a class="headerlink" href="#ssl.Purpose.CLIENT_AUTH" title="Permalink to this definition">¶</a></dt>
<dd><p>Option for <a class="reference internal" href="#ssl.create_default_context" title="ssl.create_default_context"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_default_context()</span></code></a> and
<a class="reference internal" href="#ssl.SSLContext.load_default_certs" title="ssl.SSLContext.load_default_certs"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_default_certs()</span></code></a>. This value indicates that the
context may be used to authenticate Web clients (therefore, it will
be used to create server-side sockets).</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
</div>
</div>
<div class="section" id="ssl-sockets">
<h2>17.3.2. SSL Sockets<a class="headerlink" href="#ssl-sockets" title="Permalink to this headline">¶</a></h2>
<p>SSL sockets provide the following methods of <a class="reference internal" href="socket.html#socket-objects"><span class="std std-ref">Socket Objects</span></a>:</p>
<ul class="simple">
<li><p><a class="reference internal" href="socket.html#socket.socket.accept" title="socket.socket.accept"><code class="xref py py-meth docutils literal notranslate"><span class="pre">accept()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.bind" title="socket.socket.bind"><code class="xref py py-meth docutils literal notranslate"><span class="pre">bind()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.close" title="socket.socket.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.connect" title="socket.socket.connect"><code class="xref py py-meth docutils literal notranslate"><span class="pre">connect()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.fileno" title="socket.socket.fileno"><code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.getpeername" title="socket.socket.getpeername"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getpeername()</span></code></a>, <a class="reference internal" href="socket.html#socket.socket.getsockname" title="socket.socket.getsockname"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getsockname()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.getsockopt" title="socket.socket.getsockopt"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getsockopt()</span></code></a>, <a class="reference internal" href="socket.html#socket.socket.setsockopt" title="socket.socket.setsockopt"><code class="xref py py-meth docutils literal notranslate"><span class="pre">setsockopt()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.gettimeout" title="socket.socket.gettimeout"><code class="xref py py-meth docutils literal notranslate"><span class="pre">gettimeout()</span></code></a>, <a class="reference internal" href="socket.html#socket.socket.settimeout" title="socket.socket.settimeout"><code class="xref py py-meth docutils literal notranslate"><span class="pre">settimeout()</span></code></a>,
<a class="reference internal" href="socket.html#socket.socket.setblocking" title="socket.socket.setblocking"><code class="xref py py-meth docutils literal notranslate"><span class="pre">setblocking()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.listen" title="socket.socket.listen"><code class="xref py py-meth docutils literal notranslate"><span class="pre">listen()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.makefile" title="socket.socket.makefile"><code class="xref py py-meth docutils literal notranslate"><span class="pre">makefile()</span></code></a></p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.recv" title="socket.socket.recv"><code class="xref py py-meth docutils literal notranslate"><span class="pre">recv()</span></code></a>, <a class="reference internal" href="socket.html#socket.socket.recv_into" title="socket.socket.recv_into"><code class="xref py py-meth docutils literal notranslate"><span class="pre">recv_into()</span></code></a>
(but passing a non-zero <code class="docutils literal notranslate"><span class="pre">flags</span></code> argument is not allowed)</p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.send" title="socket.socket.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code></a>, <a class="reference internal" href="socket.html#socket.socket.sendall" title="socket.socket.sendall"><code class="xref py py-meth docutils literal notranslate"><span class="pre">sendall()</span></code></a> (with
the same limitation)</p></li>
<li><p><a class="reference internal" href="socket.html#socket.socket.shutdown" title="socket.socket.shutdown"><code class="xref py py-meth docutils literal notranslate"><span class="pre">shutdown()</span></code></a></p></li>
</ul>
<p>However, since the SSL (and TLS) protocol has its own framing atop
of TCP, the SSL sockets abstraction can, in certain respects, diverge from
the specification of normal, OS-level sockets. See especially the
<a class="reference internal" href="#ssl-nonblocking"><span class="std std-ref">notes on non-blocking sockets</span></a>.</p>
<p>SSL sockets also have the following additional methods and attributes:</p>
<dl class="method">
<dt id="ssl.SSLSocket.do_handshake">
<code class="descclassname">SSLSocket.</code><code class="descname">do_handshake</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.do_handshake" title="Permalink to this definition">¶</a></dt>
<dd><p>Perform the SSL setup handshake.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.9: </span>The handshake method also performs <a class="reference internal" href="#ssl.match_hostname" title="ssl.match_hostname"><code class="xref py py-func docutils literal notranslate"><span class="pre">match_hostname()</span></code></a> when the
<a class="reference internal" href="#ssl.SSLContext.check_hostname" title="ssl.SSLContext.check_hostname"><code class="xref py py-attr docutils literal notranslate"><span class="pre">check_hostname</span></code></a> attribute of the socket’s
<a class="reference internal" href="#ssl.SSLSocket.context" title="ssl.SSLSocket.context"><code class="xref py py-attr docutils literal notranslate"><span class="pre">context</span></code></a> is true.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.getpeercert">
<code class="descclassname">SSLSocket.</code><code class="descname">getpeercert</code><span class="sig-paren">(</span><em>binary_form=False</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.getpeercert" title="Permalink to this definition">¶</a></dt>
<dd><p>If there is no certificate for the peer on the other end of the connection,
return <code class="docutils literal notranslate"><span class="pre">None</span></code>. If the SSL handshake hasn’t been done yet, raise
<a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>.</p>
<p>If the <code class="docutils literal notranslate"><span class="pre">binary_form</span></code> parameter is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a>, and a certificate was
received from the peer, this method returns a <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a> instance. If the
certificate was not validated, the dict is empty. If the certificate was
validated, it returns a dict with several keys, amongst them <code class="docutils literal notranslate"><span class="pre">subject</span></code>
(the principal for which the certificate was issued) and <code class="docutils literal notranslate"><span class="pre">issuer</span></code>
(the principal issuing the certificate). If a certificate contains an
instance of the <em>Subject Alternative Name</em> extension (see <span class="target" id="index-11"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc3280.html"><strong>RFC 3280</strong></a>),
there will also be a <code class="docutils literal notranslate"><span class="pre">subjectAltName</span></code> key in the dictionary.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">subject</span></code> and <code class="docutils literal notranslate"><span class="pre">issuer</span></code> fields are tuples containing the sequence
of relative distinguished names (RDNs) given in the certificate’s data
structure for the respective fields, and each RDN is a sequence of
name-value pairs. Here is a real-world example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">{</span><span class="s1">'issuer'</span><span class="p">:</span> <span class="p">(((</span><span class="s1">'countryName'</span><span class="p">,</span> <span class="s1">'IL'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'organizationName'</span><span class="p">,</span> <span class="s1">'StartCom Ltd.'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'organizationalUnitName'</span><span class="p">,</span>
<span class="s1">'Secure Digital Certificate Signing'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'commonName'</span><span class="p">,</span>
<span class="s1">'StartCom Class 2 Primary Intermediate Server CA'</span><span class="p">),)),</span>
<span class="s1">'notAfter'</span><span class="p">:</span> <span class="s1">'Nov 22 08:15:19 2013 GMT'</span><span class="p">,</span>
<span class="s1">'notBefore'</span><span class="p">:</span> <span class="s1">'Nov 21 03:09:52 2011 GMT'</span><span class="p">,</span>
<span class="s1">'serialNumber'</span><span class="p">:</span> <span class="s1">'95F0'</span><span class="p">,</span>
<span class="s1">'subject'</span><span class="p">:</span> <span class="p">(((</span><span class="s1">'description'</span><span class="p">,</span> <span class="s1">'571208-SLe257oHY9fVQ07Z'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'countryName'</span><span class="p">,</span> <span class="s1">'US'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'stateOrProvinceName'</span><span class="p">,</span> <span class="s1">'California'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'localityName'</span><span class="p">,</span> <span class="s1">'San Francisco'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'organizationName'</span><span class="p">,</span> <span class="s1">'Electronic Frontier Foundation, Inc.'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'commonName'</span><span class="p">,</span> <span class="s1">'*.eff.org'</span><span class="p">),),</span>
<span class="p">((</span><span class="s1">'emailAddress'</span><span class="p">,</span> <span class="s1">'hostmaster@eff.org'</span><span class="p">),)),</span>
<span class="s1">'subjectAltName'</span><span class="p">:</span> <span class="p">((</span><span class="s1">'DNS'</span><span class="p">,</span> <span class="s1">'*.eff.org'</span><span class="p">),</span> <span class="p">(</span><span class="s1">'DNS'</span><span class="p">,</span> <span class="s1">'eff.org'</span><span class="p">)),</span>
<span class="s1">'version'</span><span class="p">:</span> <span class="mi">3</span><span class="p">}</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>To validate a certificate for a particular service, you can use the
<a class="reference internal" href="#ssl.match_hostname" title="ssl.match_hostname"><code class="xref py py-func docutils literal notranslate"><span class="pre">match_hostname()</span></code></a> function.</p>
</div>
<p>If the <code class="docutils literal notranslate"><span class="pre">binary_form</span></code> parameter is <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a>, and a certificate was
provided, this method returns the DER-encoded form of the entire certificate
as a sequence of bytes, or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> if the peer did not provide a
certificate. Whether the peer provides a certificate depends on the SSL
socket’s role:</p>
<ul class="simple">
<li><p>for a client SSL socket, the server will always provide a certificate,
regardless of whether validation was required;</p></li>
<li><p>for a server SSL socket, the client will only provide a certificate
when requested by the server; therefore <a class="reference internal" href="#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal notranslate"><span class="pre">getpeercert()</span></code></a> will return
<a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> if you used <a class="reference internal" href="#ssl.CERT_NONE" title="ssl.CERT_NONE"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_NONE</span></code></a> (rather than
<a class="reference internal" href="#ssl.CERT_OPTIONAL" title="ssl.CERT_OPTIONAL"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_OPTIONAL</span></code></a> or <a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a>).</p></li>
</ul>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.9: </span>The returned dictionary includes additional items such as <code class="docutils literal notranslate"><span class="pre">issuer</span></code> and
<code class="docutils literal notranslate"><span class="pre">notBefore</span></code>. Additionall <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> is raised when the handshake
isn’t done. The returned dictionary includes additional X509v3 extension
items such as <code class="docutils literal notranslate"><span class="pre">crlDistributionPoints</span></code>, <code class="docutils literal notranslate"><span class="pre">caIssuers</span></code> and <code class="docutils literal notranslate"><span class="pre">OCSP</span></code> URIs.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.cipher">
<code class="descclassname">SSLSocket.</code><code class="descname">cipher</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.cipher" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns a three-value tuple containing the name of the cipher being used, the
version of the SSL protocol that defines its use, and the number of secret
bits being used. If no connection has been established, returns <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.compression">
<code class="descclassname">SSLSocket.</code><code class="descname">compression</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.compression" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the compression algorithm being used as a string, or <code class="docutils literal notranslate"><span class="pre">None</span></code>
if the connection isn’t compressed.</p>
<p>If the higher-level protocol supports its own compression mechanism,
you can use <a class="reference internal" href="#ssl.OP_NO_COMPRESSION" title="ssl.OP_NO_COMPRESSION"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_COMPRESSION</span></code></a> to disable SSL-level compression.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.get_channel_binding">
<code class="descclassname">SSLSocket.</code><code class="descname">get_channel_binding</code><span class="sig-paren">(</span><em>cb_type="tls-unique"</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.get_channel_binding" title="Permalink to this definition">¶</a></dt>
<dd><p>Get channel binding data for current connection, as a bytes object. Returns
<code class="docutils literal notranslate"><span class="pre">None</span></code> if not connected or the handshake has not been completed.</p>
<p>The <em>cb_type</em> parameter allow selection of the desired channel binding
type. Valid channel binding types are listed in the
<a class="reference internal" href="#ssl.CHANNEL_BINDING_TYPES" title="ssl.CHANNEL_BINDING_TYPES"><code class="xref py py-data docutils literal notranslate"><span class="pre">CHANNEL_BINDING_TYPES</span></code></a> list. Currently only the ‘tls-unique’ channel
binding, defined by <span class="target" id="index-12"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc5929.html"><strong>RFC 5929</strong></a>, is supported. <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> will be
raised if an unsupported channel binding type is requested.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.selected_alpn_protocol">
<code class="descclassname">SSLSocket.</code><code class="descname">selected_alpn_protocol</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.selected_alpn_protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the protocol that was selected during the TLS handshake. If
<a class="reference internal" href="#ssl.SSLContext.set_alpn_protocols" title="ssl.SSLContext.set_alpn_protocols"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_alpn_protocols()</span></code></a> was not called, if the other party does
not support ALPN, if this socket does not support any of the client’s
proposed protocols, or if the handshake has not happened yet, <code class="docutils literal notranslate"><span class="pre">None</span></code> is
returned.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.10.</span></p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.selected_npn_protocol">
<code class="descclassname">SSLSocket.</code><code class="descname">selected_npn_protocol</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.selected_npn_protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the higher-level protocol that was selected during the TLS/SSL
handshake. If <a class="reference internal" href="#ssl.SSLContext.set_npn_protocols" title="ssl.SSLContext.set_npn_protocols"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_npn_protocols()</span></code></a> was not called, or
if the other party does not support NPN, or if the handshake has not yet
happened, this will return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.unwrap">
<code class="descclassname">SSLSocket.</code><code class="descname">unwrap</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.unwrap" title="Permalink to this definition">¶</a></dt>
<dd><p>Performs the SSL shutdown handshake, which removes the TLS layer from the
underlying socket, and returns the underlying socket object. This can be
used to go from encrypted operation over a connection to unencrypted. The
returned socket should always be used for further communication with the
other side of the connection, rather than the original socket.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLSocket.version">
<code class="descclassname">SSLSocket.</code><code class="descname">version</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLSocket.version" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the actual SSL protocol version negotiated by the connection
as a string, or <code class="docutils literal notranslate"><span class="pre">None</span></code> is no secure connection is established.
As of this writing, possible return values include <code class="docutils literal notranslate"><span class="pre">"SSLv2"</span></code>,
<code class="docutils literal notranslate"><span class="pre">"SSLv3"</span></code>, <code class="docutils literal notranslate"><span class="pre">"TLSv1"</span></code>, <code class="docutils literal notranslate"><span class="pre">"TLSv1.1"</span></code> and <code class="docutils literal notranslate"><span class="pre">"TLSv1.2"</span></code>.
Recent OpenSSL versions may define more return values.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="ssl.SSLSocket.context">
<code class="descclassname">SSLSocket.</code><code class="descname">context</code><a class="headerlink" href="#ssl.SSLSocket.context" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> object this SSL socket is tied to. If the SSL
socket was created using the top-level <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a> function
(rather than <a class="reference internal" href="#ssl.SSLContext.wrap_socket" title="ssl.SSLContext.wrap_socket"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.wrap_socket()</span></code></a>), this is a custom context
object created for this SSL socket.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
</dd></dl>
</div>
<div class="section" id="ssl-contexts">
<h2>17.3.3. SSL Contexts<a class="headerlink" href="#ssl-contexts" title="Permalink to this headline">¶</a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.9.</span></p>
</div>
<p>An SSL context holds various data longer-lived than single SSL connections,
such as SSL configuration options, certificate(s) and private key(s).
It also manages a cache of SSL sessions for server-side sockets, in order
to speed up repeated connections from the same clients.</p>
<dl class="class">
<dt id="ssl.SSLContext">
<em class="property">class </em><code class="descclassname">ssl.</code><code class="descname">SSLContext</code><span class="sig-paren">(</span><em>protocol</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a new SSL context. You must pass <em>protocol</em> which must be one
of the <code class="docutils literal notranslate"><span class="pre">PROTOCOL_*</span></code> constants defined in this module.
<a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a> is currently recommended for maximum
interoperability.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p><a class="reference internal" href="#ssl.create_default_context" title="ssl.create_default_context"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_default_context()</span></code></a> lets the <a class="reference internal" href="#module-ssl" title="ssl: TLS/SSL wrapper for socket objects"><code class="xref py py-mod docutils literal notranslate"><span class="pre">ssl</span></code></a> module choose
security settings for a given purpose.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.16: </span>The context is created with secure default values. The options
<a class="reference internal" href="#ssl.OP_NO_COMPRESSION" title="ssl.OP_NO_COMPRESSION"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_COMPRESSION</span></code></a>, <a class="reference internal" href="#ssl.OP_CIPHER_SERVER_PREFERENCE" title="ssl.OP_CIPHER_SERVER_PREFERENCE"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_CIPHER_SERVER_PREFERENCE</span></code></a>,
<a class="reference internal" href="#ssl.OP_SINGLE_DH_USE" title="ssl.OP_SINGLE_DH_USE"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_SINGLE_DH_USE</span></code></a>, <a class="reference internal" href="#ssl.OP_SINGLE_ECDH_USE" title="ssl.OP_SINGLE_ECDH_USE"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_SINGLE_ECDH_USE</span></code></a>,
<a class="reference internal" href="#ssl.OP_NO_SSLv2" title="ssl.OP_NO_SSLv2"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_SSLv2</span></code></a> (except for <a class="reference internal" href="#ssl.PROTOCOL_SSLv2" title="ssl.PROTOCOL_SSLv2"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv2</span></code></a>),
and <a class="reference internal" href="#ssl.OP_NO_SSLv3" title="ssl.OP_NO_SSLv3"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_SSLv3</span></code></a> (except for <a class="reference internal" href="#ssl.PROTOCOL_SSLv3" title="ssl.PROTOCOL_SSLv3"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv3</span></code></a>) are
set by default. The initial cipher suite list contains only <code class="docutils literal notranslate"><span class="pre">HIGH</span></code>
ciphers, no <code class="docutils literal notranslate"><span class="pre">NULL</span></code> ciphers and no <code class="docutils literal notranslate"><span class="pre">MD5</span></code> ciphers (except for
<a class="reference internal" href="#ssl.PROTOCOL_SSLv2" title="ssl.PROTOCOL_SSLv2"><code class="xref py py-data docutils literal notranslate"><span class="pre">PROTOCOL_SSLv2</span></code></a>).</p>
</div>
</dd></dl>
<p><a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> objects have the following methods and attributes:</p>
<dl class="method">
<dt id="ssl.SSLContext.cert_store_stats">
<code class="descclassname">SSLContext.</code><code class="descname">cert_store_stats</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.cert_store_stats" title="Permalink to this definition">¶</a></dt>
<dd><p>Get statistics about quantities of loaded X.509 certificates, count of
X.509 certificates flagged as CA certificates and certificate revocation
lists as dictionary.</p>
<p>Example for a context with one CA cert and one other cert:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">cert_store_stats</span><span class="p">()</span>
<span class="go">{'crl': 0, 'x509_ca': 1, 'x509': 2}</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.load_cert_chain">
<code class="descclassname">SSLContext.</code><code class="descname">load_cert_chain</code><span class="sig-paren">(</span><em>certfile</em>, <em>keyfile=None</em>, <em>password=None</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.load_cert_chain" title="Permalink to this definition">¶</a></dt>
<dd><p>Load a private key and the corresponding certificate. The <em>certfile</em>
string must be the path to a single file in PEM format containing the
certificate as well as any number of CA certificates needed to establish
the certificate’s authenticity. The <em>keyfile</em> string, if present, must
point to a file containing the private key in. Otherwise the private
key will be taken from <em>certfile</em> as well. See the discussion of
<a class="reference internal" href="#ssl-certificates"><span class="std std-ref">Certificates</span></a> for more information on how the certificate
is stored in the <em>certfile</em>.</p>
<p>The <em>password</em> argument may be a function to call to get the password for
decrypting the private key. It will only be called if the private key is
encrypted and a password is necessary. It will be called with no arguments,
and it should return a string, bytes, or bytearray. If the return value is
a string it will be encoded as UTF-8 before using it to decrypt the key.
Alternatively a string, bytes, or bytearray value may be supplied directly
as the <em>password</em> argument. It will be ignored if the private key is not
encrypted and no password is needed.</p>
<p>If the <em>password</em> argument is not specified and a password is required,
OpenSSL’s built-in password prompting mechanism will be used to
interactively prompt the user for a password.</p>
<p>An <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLError</span></code></a> is raised if the private key doesn’t
match with the certificate.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.load_default_certs">
<code class="descclassname">SSLContext.</code><code class="descname">load_default_certs</code><span class="sig-paren">(</span><em>purpose=Purpose.SERVER_AUTH</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.load_default_certs" title="Permalink to this definition">¶</a></dt>
<dd><p>Load a set of default “certification authority” (CA) certificates from
default locations. On Windows it loads CA certs from the <code class="docutils literal notranslate"><span class="pre">CA</span></code> and
<code class="docutils literal notranslate"><span class="pre">ROOT</span></code> system stores. On other systems it calls
<a class="reference internal" href="#ssl.SSLContext.set_default_verify_paths" title="ssl.SSLContext.set_default_verify_paths"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_default_verify_paths()</span></code></a>. In the future the method may
load CA certificates from other locations, too.</p>
<p>The <em>purpose</em> flag specifies what kind of CA certificates are loaded. The
default settings <a class="reference internal" href="#ssl.Purpose.SERVER_AUTH" title="ssl.Purpose.SERVER_AUTH"><code class="xref py py-data docutils literal notranslate"><span class="pre">Purpose.SERVER_AUTH</span></code></a> loads certificates, that are
flagged and trusted for TLS web server authentication (client side
sockets). <a class="reference internal" href="#ssl.Purpose.CLIENT_AUTH" title="ssl.Purpose.CLIENT_AUTH"><code class="xref py py-data docutils literal notranslate"><span class="pre">Purpose.CLIENT_AUTH</span></code></a> loads CA certificates for client
certificate verification on the server side.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.load_verify_locations">
<code class="descclassname">SSLContext.</code><code class="descname">load_verify_locations</code><span class="sig-paren">(</span><em>cafile=None</em>, <em>capath=None</em>, <em>cadata=None</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.load_verify_locations" title="Permalink to this definition">¶</a></dt>
<dd><p>Load a set of “certification authority” (CA) certificates used to validate
other peers’ certificates when <a class="reference internal" href="#ssl.SSLContext.verify_mode" title="ssl.SSLContext.verify_mode"><code class="xref py py-data docutils literal notranslate"><span class="pre">verify_mode</span></code></a> is other than
<a class="reference internal" href="#ssl.CERT_NONE" title="ssl.CERT_NONE"><code class="xref py py-data docutils literal notranslate"><span class="pre">CERT_NONE</span></code></a>. At least one of <em>cafile</em> or <em>capath</em> must be specified.</p>
<p>This method can also load certification revocation lists (CRLs) in PEM or
DER format. In order to make use of CRLs, <a class="reference internal" href="#ssl.SSLContext.verify_flags" title="ssl.SSLContext.verify_flags"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.verify_flags</span></code></a>
must be configured properly.</p>
<p>The <em>cafile</em> string, if present, is the path to a file of concatenated
CA certificates in PEM format. See the discussion of
<a class="reference internal" href="#ssl-certificates"><span class="std std-ref">Certificates</span></a> for more information about how to arrange the
certificates in this file.</p>
<p>The <em>capath</em> string, if present, is
the path to a directory containing several CA certificates in PEM format,
following an <a class="reference external" href="https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_load_verify_locations.html">OpenSSL specific layout</a>.</p>
<p>The <em>cadata</em> object, if present, is either an ASCII string of one or more
PEM-encoded certificates or a bytes-like object of DER-encoded
certificates. Like with <em>capath</em> extra lines around PEM-encoded
certificates are ignored but at least one certificate must be present.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.get_ca_certs">
<code class="descclassname">SSLContext.</code><code class="descname">get_ca_certs</code><span class="sig-paren">(</span><em>binary_form=False</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.get_ca_certs" title="Permalink to this definition">¶</a></dt>
<dd><p>Get a list of loaded “certification authority” (CA) certificates. If the
<code class="docutils literal notranslate"><span class="pre">binary_form</span></code> parameter is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a> each list
entry is a dict like the output of <a class="reference internal" href="#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.getpeercert()</span></code></a>. Otherwise
the method returns a list of DER-encoded certificates. The returned list
does not contain certificates from <em>capath</em> unless a certificate was
requested and loaded by a SSL connection.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Certificates in a capath directory aren’t loaded unless they have
been used at least once.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.set_default_verify_paths">
<code class="descclassname">SSLContext.</code><code class="descname">set_default_verify_paths</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.set_default_verify_paths" title="Permalink to this definition">¶</a></dt>
<dd><p>Load a set of default “certification authority” (CA) certificates from
a filesystem path defined when building the OpenSSL library. Unfortunately,
there’s no easy way to know whether this method succeeds: no error is
returned if no certificates are to be found. When the OpenSSL library is
provided as part of the operating system, though, it is likely to be
configured properly.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.set_ciphers">
<code class="descclassname">SSLContext.</code><code class="descname">set_ciphers</code><span class="sig-paren">(</span><em>ciphers</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.set_ciphers" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the available ciphers for sockets created with this context.
It should be a string in the <a class="reference external" href="https://www.openssl.org/docs/manmaster/man1/ciphers.html">OpenSSL cipher list format</a>.
If no cipher can be selected (because compile-time options or other
configuration forbids use of all the specified ciphers), an
<a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLError</span></code></a> will be raised.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>when connected, the <a class="reference internal" href="#ssl.SSLSocket.cipher" title="ssl.SSLSocket.cipher"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.cipher()</span></code></a> method of SSL sockets will
give the currently selected cipher.</p>
<p>OpenSSL 1.1.1 has TLS 1.3 cipher suites enabled by default. The suites
cannot be disabled with <a class="reference internal" href="#ssl.SSLContext.set_ciphers" title="ssl.SSLContext.set_ciphers"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set_ciphers()</span></code></a>.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.set_alpn_protocols">
<code class="descclassname">SSLContext.</code><code class="descname">set_alpn_protocols</code><span class="sig-paren">(</span><em>protocols</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.set_alpn_protocols" title="Permalink to this definition">¶</a></dt>
<dd><p>Specify which protocols the socket should advertise during the SSL/TLS
handshake. It should be a list of ASCII strings, like <code class="docutils literal notranslate"><span class="pre">['http/1.1',</span>
<span class="pre">'spdy/2']</span></code>, ordered by preference. The selection of a protocol will happen
during the handshake, and will play out according to <span class="target" id="index-13"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc7301.html"><strong>RFC 7301</strong></a>. After a
successful handshake, the <a class="reference internal" href="#ssl.SSLSocket.selected_alpn_protocol" title="ssl.SSLSocket.selected_alpn_protocol"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.selected_alpn_protocol()</span></code></a> method will
return the agreed-upon protocol.</p>
<p>This method will raise <a class="reference internal" href="exceptions.html#exceptions.NotImplementedError" title="exceptions.NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> if <a class="reference internal" href="#ssl.HAS_ALPN" title="ssl.HAS_ALPN"><code class="xref py py-data docutils literal notranslate"><span class="pre">HAS_ALPN</span></code></a> is
False.</p>
<p>OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise <a class="reference internal" href="#ssl.SSLError" title="ssl.SSLError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SSLError</span></code></a>
when both sides support ALPN but cannot agree on a protocol. 1.1.0f+
behaves like 1.0.2, <a class="reference internal" href="#ssl.SSLSocket.selected_alpn_protocol" title="ssl.SSLSocket.selected_alpn_protocol"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.selected_alpn_protocol()</span></code></a> returns None.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 2.7.10.</span></p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.set_npn_protocols">
<code class="descclassname">SSLContext.</code><code class="descname">set_npn_protocols</code><span class="sig-paren">(</span><em>protocols</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.set_npn_protocols" title="Permalink to this definition">¶</a></dt>
<dd><p>Specify which protocols the socket should advertise during the SSL/TLS
handshake. It should be a list of strings, like <code class="docutils literal notranslate"><span class="pre">['http/1.1',</span> <span class="pre">'spdy/2']</span></code>,
ordered by preference. The selection of a protocol will happen during the
handshake, and will play out according to the <a class="reference external" href="https://tools.ietf.org/html/draft-agl-tls-nextprotoneg">NPN draft specification</a>. After a
successful handshake, the <a class="reference internal" href="#ssl.SSLSocket.selected_npn_protocol" title="ssl.SSLSocket.selected_npn_protocol"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.selected_npn_protocol()</span></code></a> method will
return the agreed-upon protocol.</p>
<p>This method will raise <a class="reference internal" href="exceptions.html#exceptions.NotImplementedError" title="exceptions.NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> if <a class="reference internal" href="#ssl.HAS_NPN" title="ssl.HAS_NPN"><code class="xref py py-data docutils literal notranslate"><span class="pre">HAS_NPN</span></code></a> is
False.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.set_servername_callback">
<code class="descclassname">SSLContext.</code><code class="descname">set_servername_callback</code><span class="sig-paren">(</span><em>server_name_callback</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.set_servername_callback" title="Permalink to this definition">¶</a></dt>
<dd><p>Register a callback function that will be called after the TLS Client Hello
handshake message has been received by the SSL/TLS server when the TLS client
specifies a server name indication. The server name indication mechanism
is specified in <span class="target" id="index-14"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc6066.html"><strong>RFC 6066</strong></a> section 3 - Server Name Indication.</p>
<p>Only one callback can be set per <code class="docutils literal notranslate"><span class="pre">SSLContext</span></code>. If <em>server_name_callback</em>
is <code class="docutils literal notranslate"><span class="pre">None</span></code> then the callback is disabled. Calling this function a
subsequent time will disable the previously registered callback.</p>
<p>The callback function, <em>server_name_callback</em>, will be called with three
arguments; the first being the <code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLSocket</span></code>, the second is a string
that represents the server name that the client is intending to communicate
(or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> if the TLS Client Hello does not contain a server name)
and the third argument is the original <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a>. The server name
argument is the IDNA decoded server name.</p>
<p>A typical use of this callback is to change the <code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLSocket</span></code>’s
<a class="reference internal" href="#ssl.SSLSocket.context" title="ssl.SSLSocket.context"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLSocket.context</span></code></a> attribute to a new object of type
<a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> representing a certificate chain that matches the server
name.</p>
<p>Due to the early negotiation phase of the TLS connection, only limited
methods and attributes are usable like
<a class="reference internal" href="#ssl.SSLSocket.selected_alpn_protocol" title="ssl.SSLSocket.selected_alpn_protocol"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.selected_alpn_protocol()</span></code></a> and <a class="reference internal" href="#ssl.SSLSocket.context" title="ssl.SSLSocket.context"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLSocket.context</span></code></a>.
<a class="reference internal" href="#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.getpeercert()</span></code></a>, <a class="reference internal" href="#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.getpeercert()</span></code></a>,
<a class="reference internal" href="#ssl.SSLSocket.cipher" title="ssl.SSLSocket.cipher"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.cipher()</span></code></a> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.compress()</span></code> methods require that
the TLS connection has progressed beyond the TLS Client Hello and therefore
will not contain return meaningful values nor can they be called safely.</p>
<p>The <em>server_name_callback</em> function must return <code class="docutils literal notranslate"><span class="pre">None</span></code> to allow the
TLS negotiation to continue. If a TLS failure is required, a constant
<a class="reference internal" href="#ssl.ALERT_DESCRIPTION_INTERNAL_ERROR" title="ssl.ALERT_DESCRIPTION_INTERNAL_ERROR"><code class="xref py py-const docutils literal notranslate"><span class="pre">ALERT_DESCRIPTION_*</span></code></a> can be
returned. Other return values will result in a TLS fatal error with
<a class="reference internal" href="#ssl.ALERT_DESCRIPTION_INTERNAL_ERROR" title="ssl.ALERT_DESCRIPTION_INTERNAL_ERROR"><code class="xref py py-const docutils literal notranslate"><span class="pre">ALERT_DESCRIPTION_INTERNAL_ERROR</span></code></a>.</p>
<p>If there is an IDNA decoding error on the server name, the TLS connection
will terminate with an <a class="reference internal" href="#ssl.ALERT_DESCRIPTION_INTERNAL_ERROR" title="ssl.ALERT_DESCRIPTION_INTERNAL_ERROR"><code class="xref py py-const docutils literal notranslate"><span class="pre">ALERT_DESCRIPTION_INTERNAL_ERROR</span></code></a> fatal TLS
alert message to the client.</p>
<p>If an exception is raised from the <em>server_name_callback</em> function the TLS
connection will terminate with a fatal TLS alert message
<a class="reference internal" href="#ssl.ALERT_DESCRIPTION_HANDSHAKE_FAILURE" title="ssl.ALERT_DESCRIPTION_HANDSHAKE_FAILURE"><code class="xref py py-const docutils literal notranslate"><span class="pre">ALERT_DESCRIPTION_HANDSHAKE_FAILURE</span></code></a>.</p>
<p>This method will raise <a class="reference internal" href="exceptions.html#exceptions.NotImplementedError" title="exceptions.NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> if the OpenSSL library
had OPENSSL_NO_TLSEXT defined when it was built.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.load_dh_params">
<code class="descclassname">SSLContext.</code><code class="descname">load_dh_params</code><span class="sig-paren">(</span><em>dhfile</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.load_dh_params" title="Permalink to this definition">¶</a></dt>
<dd><p>Load the key generation parameters for Diffie-Helman (DH) key exchange.
Using DH key exchange improves forward secrecy at the expense of
computational resources (both on the server and on the client).
The <em>dhfile</em> parameter should be the path to a file containing DH
parameters in PEM format.</p>
<p>This setting doesn’t apply to client sockets. You can also use the
<a class="reference internal" href="#ssl.OP_SINGLE_DH_USE" title="ssl.OP_SINGLE_DH_USE"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_SINGLE_DH_USE</span></code></a> option to further improve security.</p>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.set_ecdh_curve">
<code class="descclassname">SSLContext.</code><code class="descname">set_ecdh_curve</code><span class="sig-paren">(</span><em>curve_name</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.set_ecdh_curve" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the curve name for Elliptic Curve-based Diffie-Hellman (ECDH) key
exchange. ECDH is significantly faster than regular DH while arguably
as secure. The <em>curve_name</em> parameter should be a string describing
a well-known elliptic curve, for example <code class="docutils literal notranslate"><span class="pre">prime256v1</span></code> for a widely
supported curve.</p>
<p>This setting doesn’t apply to client sockets. You can also use the
<a class="reference internal" href="#ssl.OP_SINGLE_ECDH_USE" title="ssl.OP_SINGLE_ECDH_USE"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_SINGLE_ECDH_USE</span></code></a> option to further improve security.</p>
<p>This method is not available if <a class="reference internal" href="#ssl.HAS_ECDH" title="ssl.HAS_ECDH"><code class="xref py py-data docutils literal notranslate"><span class="pre">HAS_ECDH</span></code></a> is <code class="docutils literal notranslate"><span class="pre">False</span></code>.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><a class="reference external" href="http://vincent.bernat.im/en/blog/2011-ssl-perfect-forward-secrecy.html">SSL/TLS & Perfect Forward Secrecy</a></dt><dd><p>Vincent Bernat.</p>
</dd>
</dl>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.wrap_socket">
<code class="descclassname">SSLContext.</code><code class="descname">wrap_socket</code><span class="sig-paren">(</span><em>sock</em>, <em>server_side=False</em>, <em>do_handshake_on_connect=True</em>, <em>suppress_ragged_eofs=True</em>, <em>server_hostname=None</em><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.wrap_socket" title="Permalink to this definition">¶</a></dt>
<dd><p>Wrap an existing Python socket <em>sock</em> and return an <code class="xref py py-class docutils literal notranslate"><span class="pre">SSLSocket</span></code>
object. <em>sock</em> must be a <a class="reference internal" href="socket.html#socket.SOCK_STREAM" title="socket.SOCK_STREAM"><code class="xref py py-data docutils literal notranslate"><span class="pre">SOCK_STREAM</span></code></a> socket; other socket
types are unsupported.</p>
<p>The returned SSL socket is tied to the context, its settings and
certificates. The parameters <em>server_side</em>, <em>do_handshake_on_connect</em>
and <em>suppress_ragged_eofs</em> have the same meaning as in the top-level
<a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a> function.</p>
<p>On client connections, the optional parameter <em>server_hostname</em> specifies
the hostname of the service which we are connecting to. This allows a
single server to host multiple SSL-based services with distinct certificates,
quite similarly to HTTP virtual hosts. Specifying <em>server_hostname</em> will
raise a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> if <em>server_side</em> is true.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 2.7.9: </span>Always allow a server_hostname to be passed, even if OpenSSL does not
have SNI.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="ssl.SSLContext.session_stats">
<code class="descclassname">SSLContext.</code><code class="descname">session_stats</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#ssl.SSLContext.session_stats" title="Permalink to this definition">¶</a></dt>
<dd><p>Get statistics about the SSL sessions created or managed by this context.
A dictionary is returned which maps the names of each <a class="reference external" href="https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_sess_number.html">piece of information</a> to their
numeric values. For example, here is the total number of hits and misses
in the session cache since the context was created:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">stats</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="n">session_stats</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">stats</span><span class="p">[</span><span class="s1">'hits'</span><span class="p">],</span> <span class="n">stats</span><span class="p">[</span><span class="s1">'misses'</span><span class="p">]</span>
<span class="go">(0, 0)</span>
</pre></div>
</div>
</dd></dl>
<dl class="attribute">
<dt id="ssl.SSLContext.check_hostname">
<code class="descclassname">SSLContext.</code><code class="descname">check_hostname</code><a class="headerlink" href="#ssl.SSLContext.check_hostname" title="Permalink to this definition">¶</a></dt>
<dd><p>Wether to match the peer cert’s hostname with <a class="reference internal" href="#ssl.match_hostname" title="ssl.match_hostname"><code class="xref py py-func docutils literal notranslate"><span class="pre">match_hostname()</span></code></a> in
<a class="reference internal" href="#ssl.SSLSocket.do_handshake" title="ssl.SSLSocket.do_handshake"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.do_handshake()</span></code></a>. The context’s
<a class="reference internal" href="#ssl.SSLContext.verify_mode" title="ssl.SSLContext.verify_mode"><code class="xref py py-attr docutils literal notranslate"><span class="pre">verify_mode</span></code></a> must be set to <a class="reference internal" href="#ssl.CERT_OPTIONAL" title="ssl.CERT_OPTIONAL"><code class="xref py py-data docutils literal notranslate"><span class="pre">CERT_OPTIONAL</span></code></a> or
<a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-data docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a>, and you must pass <em>server_hostname</em> to
<a class="reference internal" href="#ssl.SSLContext.wrap_socket" title="ssl.SSLContext.wrap_socket"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a> in order to match the hostname.</p>
<p>Example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">socket</span><span class="o">,</span> <span class="nn">ssl</span>
<span class="n">context</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">SSLContext</span><span class="p">(</span><span class="n">ssl</span><span class="o">.</span><span class="n">PROTOCOL_TLS</span><span class="p">)</span>
<span class="n">context</span><span class="o">.</span><span class="n">verify_mode</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">CERT_REQUIRED</span>
<span class="n">context</span><span class="o">.</span><span class="n">check_hostname</span> <span class="o">=</span> <span class="kc">True</span>
<span class="n">context</span><span class="o">.</span><span class="n">load_default_certs</span><span class="p">()</span>
<span class="n">s</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">AF_INET</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">SOCK_STREAM</span><span class="p">)</span>
<span class="n">ssl_sock</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="n">wrap_socket</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">server_hostname</span><span class="o">=</span><span class="s1">'www.verisign.com'</span><span class="p">)</span>
<span class="n">ssl_sock</span><span class="o">.</span><span class="n">connect</span><span class="p">((</span><span class="s1">'www.verisign.com'</span><span class="p">,</span> <span class="mi">443</span><span class="p">))</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>This features requires OpenSSL 0.9.8f or newer.</p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="ssl.SSLContext.options">
<code class="descclassname">SSLContext.</code><code class="descname">options</code><a class="headerlink" href="#ssl.SSLContext.options" title="Permalink to this definition">¶</a></dt>
<dd><p>An integer representing the set of SSL options enabled on this context.
The default value is <a class="reference internal" href="#ssl.OP_ALL" title="ssl.OP_ALL"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_ALL</span></code></a>, but you can specify other options
such as <a class="reference internal" href="#ssl.OP_NO_SSLv2" title="ssl.OP_NO_SSLv2"><code class="xref py py-data docutils literal notranslate"><span class="pre">OP_NO_SSLv2</span></code></a> by ORing them together.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>With versions of OpenSSL older than 0.9.8m, it is only possible
to set options, not to clear them. Attempting to clear an option
(by resetting the corresponding bits) will raise a <code class="docutils literal notranslate"><span class="pre">ValueError</span></code>.</p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="ssl.SSLContext.protocol">
<code class="descclassname">SSLContext.</code><code class="descname">protocol</code><a class="headerlink" href="#ssl.SSLContext.protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>The protocol version chosen when constructing the context. This attribute
is read-only.</p>
</dd></dl>
<dl class="attribute">
<dt id="ssl.SSLContext.verify_flags">
<code class="descclassname">SSLContext.</code><code class="descname">verify_flags</code><a class="headerlink" href="#ssl.SSLContext.verify_flags" title="Permalink to this definition">¶</a></dt>
<dd><p>The flags for certificate verification operations. You can set flags like
<a class="reference internal" href="#ssl.VERIFY_CRL_CHECK_LEAF" title="ssl.VERIFY_CRL_CHECK_LEAF"><code class="xref py py-data docutils literal notranslate"><span class="pre">VERIFY_CRL_CHECK_LEAF</span></code></a> by ORing them together. By default OpenSSL
does neither require nor verify certificate revocation lists (CRLs).
Available only with openssl version 0.9.8+.</p>
</dd></dl>
<dl class="attribute">
<dt id="ssl.SSLContext.verify_mode">
<code class="descclassname">SSLContext.</code><code class="descname">verify_mode</code><a class="headerlink" href="#ssl.SSLContext.verify_mode" title="Permalink to this definition">¶</a></dt>
<dd><p>Whether to try to verify other peers’ certificates and how to behave
if verification fails. This attribute must be one of
<a class="reference internal" href="#ssl.CERT_NONE" title="ssl.CERT_NONE"><code class="xref py py-data docutils literal notranslate"><span class="pre">CERT_NONE</span></code></a>, <a class="reference internal" href="#ssl.CERT_OPTIONAL" title="ssl.CERT_OPTIONAL"><code class="xref py py-data docutils literal notranslate"><span class="pre">CERT_OPTIONAL</span></code></a> or <a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-data docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a>.</p>
</dd></dl>
<span class="target" id="index-15"></span></div>
<div class="section" id="certificates">
<span id="ssl-certificates"></span><span id="index-16"></span><h2>17.3.4. Certificates<a class="headerlink" href="#certificates" title="Permalink to this headline">¶</a></h2>
<p>Certificates in general are part of a public-key / private-key system. In this
system, each <em>principal</em>, (which may be a machine, or a person, or an
organization) is assigned a unique two-part encryption key. One part of the key
is public, and is called the <em>public key</em>; the other part is kept secret, and is
called the <em>private key</em>. The two parts are related, in that if you encrypt a
message with one of the parts, you can decrypt it with the other part, and
<strong>only</strong> with the other part.</p>
<p>A certificate contains information about two principals. It contains the name
of a <em>subject</em>, and the subject’s public key. It also contains a statement by a
second principal, the <em>issuer</em>, that the subject is who they claim to be, and
that this is indeed the subject’s public key. The issuer’s statement is signed
with the issuer’s private key, which only the issuer knows. However, anyone can
verify the issuer’s statement by finding the issuer’s public key, decrypting the
statement with it, and comparing it to the other information in the certificate.
The certificate also contains information about the time period over which it is
valid. This is expressed as two fields, called “notBefore” and “notAfter”.</p>
<p>In the Python use of certificates, a client or server can use a certificate to
prove who they are. The other side of a network connection can also be required
to produce a certificate, and that certificate can be validated to the
satisfaction of the client or server that requires such validation. The
connection attempt can be set to raise an exception if the validation fails.
Validation is done automatically, by the underlying OpenSSL framework; the
application need not concern itself with its mechanics. But the application
does usually need to provide sets of certificates to allow this process to take
place.</p>
<p>Python uses files to contain certificates. They should be formatted as “PEM”
(see <span class="target" id="index-17"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc1422.html"><strong>RFC 1422</strong></a>), which is a base-64 encoded form wrapped with a header line
and a footer line:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">-----</span><span class="n">BEGIN</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
<span class="o">...</span> <span class="p">(</span><span class="n">certificate</span> <span class="ow">in</span> <span class="n">base64</span> <span class="n">PEM</span> <span class="n">encoding</span><span class="p">)</span> <span class="o">...</span>
<span class="o">-----</span><span class="n">END</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
</pre></div>
</div>
<div class="section" id="certificate-chains">
<h3>17.3.4.1. Certificate chains<a class="headerlink" href="#certificate-chains" title="Permalink to this headline">¶</a></h3>
<p>The Python files which contain certificates can contain a sequence of
certificates, sometimes called a <em>certificate chain</em>. This chain should start
with the specific certificate for the principal who “is” the client or server,
and then the certificate for the issuer of that certificate, and then the
certificate for the issuer of <em>that</em> certificate, and so on up the chain till
you get to a certificate which is <em>self-signed</em>, that is, a certificate which
has the same subject and issuer, sometimes called a <em>root certificate</em>. The
certificates should just be concatenated together in the certificate file. For
example, suppose we had a three certificate chain, from our server certificate
to the certificate of the certification authority that signed our server
certificate, to the root certificate of the agency which issued the
certification authority’s certificate:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">-----</span><span class="n">BEGIN</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
<span class="o">...</span> <span class="p">(</span><span class="n">certificate</span> <span class="k">for</span> <span class="n">your</span> <span class="n">server</span><span class="p">)</span><span class="o">...</span>
<span class="o">-----</span><span class="n">END</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
<span class="o">-----</span><span class="n">BEGIN</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
<span class="o">...</span> <span class="p">(</span><span class="n">the</span> <span class="n">certificate</span> <span class="k">for</span> <span class="n">the</span> <span class="n">CA</span><span class="p">)</span><span class="o">...</span>
<span class="o">-----</span><span class="n">END</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
<span class="o">-----</span><span class="n">BEGIN</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
<span class="o">...</span> <span class="p">(</span><span class="n">the</span> <span class="n">root</span> <span class="n">certificate</span> <span class="k">for</span> <span class="n">the</span> <span class="n">CA</span><span class="s1">'s issuer)...</span>
<span class="o">-----</span><span class="n">END</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
</pre></div>
</div>
</div>
<div class="section" id="ca-certificates">
<h3>17.3.4.2. CA certificates<a class="headerlink" href="#ca-certificates" title="Permalink to this headline">¶</a></h3>
<p>If you are going to require validation of the other side of the connection’s
certificate, you need to provide a “CA certs” file, filled with the certificate
chains for each issuer you are willing to trust. Again, this file just contains
these chains concatenated together. For validation, Python will use the first
chain it finds in the file which matches. The platform’s certificates file can
be used by calling <a class="reference internal" href="#ssl.SSLContext.load_default_certs" title="ssl.SSLContext.load_default_certs"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_default_certs()</span></code></a>, this is done
automatically with <a class="reference internal" href="#ssl.create_default_context" title="ssl.create_default_context"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_default_context()</span></code></a>.</p>
</div>
<div class="section" id="combined-key-and-certificate">
<h3>17.3.4.3. Combined key and certificate<a class="headerlink" href="#combined-key-and-certificate" title="Permalink to this headline">¶</a></h3>
<p>Often the private key is stored in the same file as the certificate; in this
case, only the <code class="docutils literal notranslate"><span class="pre">certfile</span></code> parameter to <a class="reference internal" href="#ssl.SSLContext.load_cert_chain" title="ssl.SSLContext.load_cert_chain"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_cert_chain()</span></code></a>
and <a class="reference internal" href="#ssl.wrap_socket" title="ssl.wrap_socket"><code class="xref py py-func docutils literal notranslate"><span class="pre">wrap_socket()</span></code></a> needs to be passed. If the private key is stored
with the certificate, it should come before the first certificate in
the certificate chain:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">-----</span><span class="n">BEGIN</span> <span class="n">RSA</span> <span class="n">PRIVATE</span> <span class="n">KEY</span><span class="o">-----</span>
<span class="o">...</span> <span class="p">(</span><span class="n">private</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">base64</span> <span class="n">encoding</span><span class="p">)</span> <span class="o">...</span>
<span class="o">-----</span><span class="n">END</span> <span class="n">RSA</span> <span class="n">PRIVATE</span> <span class="n">KEY</span><span class="o">-----</span>
<span class="o">-----</span><span class="n">BEGIN</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
<span class="o">...</span> <span class="p">(</span><span class="n">certificate</span> <span class="ow">in</span> <span class="n">base64</span> <span class="n">PEM</span> <span class="n">encoding</span><span class="p">)</span> <span class="o">...</span>
<span class="o">-----</span><span class="n">END</span> <span class="n">CERTIFICATE</span><span class="o">-----</span>
</pre></div>
</div>
</div>
<div class="section" id="self-signed-certificates">
<h3>17.3.4.4. Self-signed certificates<a class="headerlink" href="#self-signed-certificates" title="Permalink to this headline">¶</a></h3>
<p>If you are going to create a server that provides SSL-encrypted connection
services, you will need to acquire a certificate for that service. There are
many ways of acquiring appropriate certificates, such as buying one from a
certification authority. Another common practice is to generate a self-signed
certificate. The simplest way to do this is with the OpenSSL package, using
something like the following:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">%</span> <span class="n">openssl</span> <span class="n">req</span> <span class="o">-</span><span class="n">new</span> <span class="o">-</span><span class="n">x509</span> <span class="o">-</span><span class="n">days</span> <span class="mi">365</span> <span class="o">-</span><span class="n">nodes</span> <span class="o">-</span><span class="n">out</span> <span class="n">cert</span><span class="o">.</span><span class="n">pem</span> <span class="o">-</span><span class="n">keyout</span> <span class="n">cert</span><span class="o">.</span><span class="n">pem</span>
<span class="n">Generating</span> <span class="n">a</span> <span class="mi">1024</span> <span class="n">bit</span> <span class="n">RSA</span> <span class="n">private</span> <span class="n">key</span>
<span class="o">.......++++++</span>
<span class="o">.............................++++++</span>
<span class="n">writing</span> <span class="n">new</span> <span class="n">private</span> <span class="n">key</span> <span class="n">to</span> <span class="s1">'cert.pem'</span>
<span class="o">-----</span>
<span class="n">You</span> <span class="n">are</span> <span class="n">about</span> <span class="n">to</span> <span class="n">be</span> <span class="n">asked</span> <span class="n">to</span> <span class="n">enter</span> <span class="n">information</span> <span class="n">that</span> <span class="n">will</span> <span class="n">be</span> <span class="n">incorporated</span>
<span class="n">into</span> <span class="n">your</span> <span class="n">certificate</span> <span class="n">request</span><span class="o">.</span>
<span class="n">What</span> <span class="n">you</span> <span class="n">are</span> <span class="n">about</span> <span class="n">to</span> <span class="n">enter</span> <span class="ow">is</span> <span class="n">what</span> <span class="ow">is</span> <span class="n">called</span> <span class="n">a</span> <span class="n">Distinguished</span> <span class="n">Name</span> <span class="ow">or</span> <span class="n">a</span> <span class="n">DN</span><span class="o">.</span>
<span class="n">There</span> <span class="n">are</span> <span class="n">quite</span> <span class="n">a</span> <span class="n">few</span> <span class="n">fields</span> <span class="n">but</span> <span class="n">you</span> <span class="n">can</span> <span class="n">leave</span> <span class="n">some</span> <span class="n">blank</span>
<span class="n">For</span> <span class="n">some</span> <span class="n">fields</span> <span class="n">there</span> <span class="n">will</span> <span class="n">be</span> <span class="n">a</span> <span class="n">default</span> <span class="n">value</span><span class="p">,</span>
<span class="n">If</span> <span class="n">you</span> <span class="n">enter</span> <span class="s1">'.'</span><span class="p">,</span> <span class="n">the</span> <span class="n">field</span> <span class="n">will</span> <span class="n">be</span> <span class="n">left</span> <span class="n">blank</span><span class="o">.</span>
<span class="o">-----</span>
<span class="n">Country</span> <span class="n">Name</span> <span class="p">(</span><span class="mi">2</span> <span class="n">letter</span> <span class="n">code</span><span class="p">)</span> <span class="p">[</span><span class="n">AU</span><span class="p">]:</span><span class="n">US</span>
<span class="n">State</span> <span class="ow">or</span> <span class="n">Province</span> <span class="n">Name</span> <span class="p">(</span><span class="n">full</span> <span class="n">name</span><span class="p">)</span> <span class="p">[</span><span class="n">Some</span><span class="o">-</span><span class="n">State</span><span class="p">]:</span><span class="n">MyState</span>
<span class="n">Locality</span> <span class="n">Name</span> <span class="p">(</span><span class="n">eg</span><span class="p">,</span> <span class="n">city</span><span class="p">)</span> <span class="p">[]:</span><span class="n">Some</span> <span class="n">City</span>
<span class="n">Organization</span> <span class="n">Name</span> <span class="p">(</span><span class="n">eg</span><span class="p">,</span> <span class="n">company</span><span class="p">)</span> <span class="p">[</span><span class="n">Internet</span> <span class="n">Widgits</span> <span class="n">Pty</span> <span class="n">Ltd</span><span class="p">]:</span><span class="n">My</span> <span class="n">Organization</span><span class="p">,</span> <span class="n">Inc</span><span class="o">.</span>
<span class="n">Organizational</span> <span class="n">Unit</span> <span class="n">Name</span> <span class="p">(</span><span class="n">eg</span><span class="p">,</span> <span class="n">section</span><span class="p">)</span> <span class="p">[]:</span><span class="n">My</span> <span class="n">Group</span>
<span class="n">Common</span> <span class="n">Name</span> <span class="p">(</span><span class="n">eg</span><span class="p">,</span> <span class="n">YOUR</span> <span class="n">name</span><span class="p">)</span> <span class="p">[]:</span><span class="n">myserver</span><span class="o">.</span><span class="n">mygroup</span><span class="o">.</span><span class="n">myorganization</span><span class="o">.</span><span class="n">com</span>
<span class="n">Email</span> <span class="n">Address</span> <span class="p">[]:</span><span class="n">ops</span><span class="nd">@myserver</span><span class="o">.</span><span class="n">mygroup</span><span class="o">.</span><span class="n">myorganization</span><span class="o">.</span><span class="n">com</span>
<span class="o">%</span>
</pre></div>
</div>
<p>The disadvantage of a self-signed certificate is that it is its own root
certificate, and no one else will have it in their cache of known (and trusted)
root certificates.</p>
</div>
</div>
<div class="section" id="examples">
<h2>17.3.5. Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="section" id="testing-for-ssl-support">
<h3>17.3.5.1. Testing for SSL support<a class="headerlink" href="#testing-for-ssl-support" title="Permalink to this headline">¶</a></h3>
<p>To test for the presence of SSL support in a Python installation, user code
should use the following idiom:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span>
<span class="kn">import</span> <span class="nn">ssl</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
<span class="k">pass</span>
<span class="k">else</span><span class="p">:</span>
<span class="o">...</span> <span class="c1"># do something that requires SSL support</span>
</pre></div>
</div>
</div>
<div class="section" id="client-side-operation">
<h3>17.3.5.2. Client-side operation<a class="headerlink" href="#client-side-operation" title="Permalink to this headline">¶</a></h3>
<p>This example creates a SSL context with the recommended security settings
for client sockets, including automatic certificate verification:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">create_default_context</span><span class="p">()</span>
</pre></div>
</div>
<p>If you prefer to tune security settings yourself, you might create
a context from scratch (but beware that you might not get the settings
right):</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">SSLContext</span><span class="p">(</span><span class="n">ssl</span><span class="o">.</span><span class="n">PROTOCOL_TLS</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">verify_mode</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">CERT_REQUIRED</span>
<span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">check_hostname</span> <span class="o">=</span> <span class="kc">True</span>
<span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">load_verify_locations</span><span class="p">(</span><span class="s2">"/etc/ssl/certs/ca-bundle.crt"</span><span class="p">)</span>
</pre></div>
</div>
<p>(this snippet assumes your operating system places a bundle of all CA
certificates in <code class="docutils literal notranslate"><span class="pre">/etc/ssl/certs/ca-bundle.crt</span></code>; if not, you’ll get an
error and have to adjust the location)</p>
<p>When you use the context to connect to a server, <a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a>
validates the server certificate: it ensures that the server certificate
was signed with one of the CA certificates, and checks the signature for
correctness:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">conn</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="n">wrap_socket</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">AF_INET</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">server_hostname</span><span class="o">=</span><span class="s2">"www.python.org"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">conn</span><span class="o">.</span><span class="n">connect</span><span class="p">((</span><span class="s2">"www.python.org"</span><span class="p">,</span> <span class="mi">443</span><span class="p">))</span>
</pre></div>
</div>
<p>You may then fetch the certificate:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">cert</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="n">getpeercert</span><span class="p">()</span>
</pre></div>
</div>
<p>Visual inspection shows that the certificate does identify the desired service
(that is, the HTTPS host <code class="docutils literal notranslate"><span class="pre">www.python.org</span></code>):</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pprint</span><span class="o">.</span><span class="n">pprint</span><span class="p">(</span><span class="n">cert</span><span class="p">)</span>
<span class="go">{'OCSP': ('http://ocsp.digicert.com',),</span>
<span class="go"> 'caIssuers': ('http://cacerts.digicert.com/DigiCertSHA2ExtendedValidationServerCA.crt',),</span>
<span class="go"> 'crlDistributionPoints': ('http://crl3.digicert.com/sha2-ev-server-g1.crl',</span>
<span class="go"> 'http://crl4.digicert.com/sha2-ev-server-g1.crl'),</span>
<span class="go"> 'issuer': ((('countryName', 'US'),),</span>
<span class="go"> (('organizationName', 'DigiCert Inc'),),</span>
<span class="go"> (('organizationalUnitName', 'www.digicert.com'),),</span>
<span class="go"> (('commonName', 'DigiCert SHA2 Extended Validation Server CA'),)),</span>
<span class="go"> 'notAfter': 'Sep 9 12:00:00 2016 GMT',</span>
<span class="go"> 'notBefore': 'Sep 5 00:00:00 2014 GMT',</span>
<span class="go"> 'serialNumber': '01BB6F00122B177F36CAB49CEA8B6B26',</span>
<span class="go"> 'subject': ((('businessCategory', 'Private Organization'),),</span>
<span class="go"> (('1.3.6.1.4.1.311.60.2.1.3', 'US'),),</span>
<span class="go"> (('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),),</span>
<span class="go"> (('serialNumber', '3359300'),),</span>
<span class="go"> (('streetAddress', '16 Allen Rd'),),</span>
<span class="go"> (('postalCode', '03894-4801'),),</span>
<span class="go"> (('countryName', 'US'),),</span>
<span class="go"> (('stateOrProvinceName', 'NH'),),</span>
<span class="go"> (('localityName', 'Wolfeboro,'),),</span>
<span class="go"> (('organizationName', 'Python Software Foundation'),),</span>
<span class="go"> (('commonName', 'www.python.org'),)),</span>
<span class="go"> 'subjectAltName': (('DNS', 'www.python.org'),</span>
<span class="go"> ('DNS', 'python.org'),</span>
<span class="go"> ('DNS', 'pypi.org'),</span>
<span class="go"> ('DNS', 'docs.python.org'),</span>
<span class="go"> ('DNS', 'testpypi.python.org'),</span>
<span class="go"> ('DNS', 'bugs.python.org'),</span>
<span class="go"> ('DNS', 'wiki.python.org'),</span>
<span class="go"> ('DNS', 'hg.python.org'),</span>
<span class="go"> ('DNS', 'mail.python.org'),</span>
<span class="go"> ('DNS', 'packaging.python.org'),</span>
<span class="go"> ('DNS', 'pythonhosted.org'),</span>
<span class="go"> ('DNS', 'www.pythonhosted.org'),</span>
<span class="go"> ('DNS', 'test.pythonhosted.org'),</span>
<span class="go"> ('DNS', 'us.pycon.org'),</span>
<span class="go"> ('DNS', 'id.python.org')),</span>
<span class="go"> 'version': 3}</span>
</pre></div>
</div>
<p>Now the SSL channel is established and the certificate verified, you can
proceed to talk with the server:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">conn</span><span class="o">.</span><span class="n">sendall</span><span class="p">(</span><span class="sa">b</span><span class="s2">"HEAD / HTTP/1.0</span><span class="se">\r\n</span><span class="s2">Host: linuxfr.org</span><span class="se">\r\n\r\n</span><span class="s2">"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">pprint</span><span class="o">.</span><span class="n">pprint</span><span class="p">(</span><span class="n">conn</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1024</span><span class="p">)</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">b</span><span class="s2">"</span><span class="se">\r\n</span><span class="s2">"</span><span class="p">))</span>
<span class="go">[b'HTTP/1.1 200 OK',</span>
<span class="go"> b'Date: Sat, 18 Oct 2014 18:27:20 GMT',</span>
<span class="go"> b'Server: nginx',</span>
<span class="go"> b'Content-Type: text/html; charset=utf-8',</span>
<span class="go"> b'X-Frame-Options: SAMEORIGIN',</span>
<span class="go"> b'Content-Length: 45679',</span>
<span class="go"> b'Accept-Ranges: bytes',</span>
<span class="go"> b'Via: 1.1 varnish',</span>
<span class="go"> b'Age: 2188',</span>
<span class="go"> b'X-Served-By: cache-lcy1134-LCY',</span>
<span class="go"> b'X-Cache: HIT',</span>
<span class="go"> b'X-Cache-Hits: 11',</span>
<span class="go"> b'Vary: Cookie',</span>
<span class="go"> b'Strict-Transport-Security: max-age=63072000; includeSubDomains',</span>
<span class="go"> b'Connection: close',</span>
<span class="go"> b'',</span>
<span class="go"> b'']</span>
</pre></div>
</div>
<p>See the discussion of <a class="reference internal" href="#ssl-security"><span class="std std-ref">Security considerations</span></a> below.</p>
</div>
<div class="section" id="server-side-operation">
<h3>17.3.5.3. Server-side operation<a class="headerlink" href="#server-side-operation" title="Permalink to this headline">¶</a></h3>
<p>For server operation, typically you’ll need to have a server certificate, and
private key, each in a file. You’ll first create a context holding the key
and the certificate, so that clients can check your authenticity. Then
you’ll open a socket, bind it to a port, call <code class="xref py py-meth docutils literal notranslate"><span class="pre">listen()</span></code> on it, and start
waiting for clients to connect:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">socket</span><span class="o">,</span> <span class="nn">ssl</span>
<span class="n">context</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">create_default_context</span><span class="p">(</span><span class="n">ssl</span><span class="o">.</span><span class="n">Purpose</span><span class="o">.</span><span class="n">CLIENT_AUTH</span><span class="p">)</span>
<span class="n">context</span><span class="o">.</span><span class="n">load_cert_chain</span><span class="p">(</span><span class="n">certfile</span><span class="o">=</span><span class="s2">"mycertfile"</span><span class="p">,</span> <span class="n">keyfile</span><span class="o">=</span><span class="s2">"mykeyfile"</span><span class="p">)</span>
<span class="n">bindsocket</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">()</span>
<span class="n">bindsocket</span><span class="o">.</span><span class="n">bind</span><span class="p">((</span><span class="s1">'myaddr.mydomain.com'</span><span class="p">,</span> <span class="mi">10023</span><span class="p">))</span>
<span class="n">bindsocket</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
</pre></div>
</div>
<p>When a client connects, you’ll call <code class="xref py py-meth docutils literal notranslate"><span class="pre">accept()</span></code> on the socket to get the
new socket from the other end, and use the context’s <a class="reference internal" href="#ssl.SSLContext.wrap_socket" title="ssl.SSLContext.wrap_socket"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.wrap_socket()</span></code></a>
method to create a server-side SSL socket for the connection:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="n">newsocket</span><span class="p">,</span> <span class="n">fromaddr</span> <span class="o">=</span> <span class="n">bindsocket</span><span class="o">.</span><span class="n">accept</span><span class="p">()</span>
<span class="n">connstream</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="n">wrap_socket</span><span class="p">(</span><span class="n">newsocket</span><span class="p">,</span> <span class="n">server_side</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">deal_with_client</span><span class="p">(</span><span class="n">connstream</span><span class="p">)</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">connstream</span><span class="o">.</span><span class="n">shutdown</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">SHUT_RDWR</span><span class="p">)</span>
<span class="n">connstream</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>Then you’ll read data from the <code class="docutils literal notranslate"><span class="pre">connstream</span></code> and do something with it till you
are finished with the client (or the client is finished with you):</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">deal_with_client</span><span class="p">(</span><span class="n">connstream</span><span class="p">):</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">connstream</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="c1"># null data means the client is finished with us</span>
<span class="k">while</span> <span class="n">data</span><span class="p">:</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">do_something</span><span class="p">(</span><span class="n">connstream</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
<span class="c1"># we'll assume do_something returns False</span>
<span class="c1"># when we're finished with client</span>
<span class="k">break</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">connstream</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="c1"># finished with client</span>
</pre></div>
</div>
<p>And go back to listening for new client connections (of course, a real server
would probably handle each client connection in a separate thread, or put
the sockets in non-blocking mode and use an event loop).</p>
</div>
</div>
<div class="section" id="notes-on-non-blocking-sockets">
<span id="ssl-nonblocking"></span><h2>17.3.6. Notes on non-blocking sockets<a class="headerlink" href="#notes-on-non-blocking-sockets" title="Permalink to this headline">¶</a></h2>
<p>When working with non-blocking sockets, there are several things you need
to be aware of:</p>
<ul>
<li><p>Calling <a class="reference internal" href="select.html#select.select" title="select.select"><code class="xref py py-func docutils literal notranslate"><span class="pre">select()</span></code></a> tells you that the OS-level socket can be
read from (or written to), but it does not imply that there is sufficient
data at the upper SSL layer. For example, only part of an SSL frame might
have arrived. Therefore, you must be ready to handle <code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.recv()</span></code>
and <code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.send()</span></code> failures, and retry after another call to
<a class="reference internal" href="select.html#select.select" title="select.select"><code class="xref py py-func docutils literal notranslate"><span class="pre">select()</span></code></a>.</p></li>
<li><p>Conversely, since the SSL layer has its own framing, a SSL socket may
still have data available for reading without <a class="reference internal" href="select.html#select.select" title="select.select"><code class="xref py py-func docutils literal notranslate"><span class="pre">select()</span></code></a>
being aware of it. Therefore, you should first call
<code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.recv()</span></code> to drain any potentially available data, and then
only block on a <a class="reference internal" href="select.html#select.select" title="select.select"><code class="xref py py-func docutils literal notranslate"><span class="pre">select()</span></code></a> call if still necessary.</p>
<p>(of course, similar provisions apply when using other primitives such as
<a class="reference internal" href="select.html#select.poll" title="select.poll"><code class="xref py py-func docutils literal notranslate"><span class="pre">poll()</span></code></a>, or those in the <code class="xref py py-mod docutils literal notranslate"><span class="pre">selectors</span></code> module)</p>
</li>
<li><p>The SSL handshake itself will be non-blocking: the
<a class="reference internal" href="#ssl.SSLSocket.do_handshake" title="ssl.SSLSocket.do_handshake"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.do_handshake()</span></code></a> method has to be retried until it returns
successfully. Here is a synopsis using <a class="reference internal" href="select.html#select.select" title="select.select"><code class="xref py py-func docutils literal notranslate"><span class="pre">select()</span></code></a> to wait for
the socket’s readiness:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">sock</span><span class="o">.</span><span class="n">do_handshake</span><span class="p">()</span>
<span class="k">break</span>
<span class="k">except</span> <span class="n">ssl</span><span class="o">.</span><span class="n">SSLWantReadError</span><span class="p">:</span>
<span class="n">select</span><span class="o">.</span><span class="n">select</span><span class="p">([</span><span class="n">sock</span><span class="p">],</span> <span class="p">[],</span> <span class="p">[])</span>
<span class="k">except</span> <span class="n">ssl</span><span class="o">.</span><span class="n">SSLWantWriteError</span><span class="p">:</span>
<span class="n">select</span><span class="o">.</span><span class="n">select</span><span class="p">([],</span> <span class="p">[</span><span class="n">sock</span><span class="p">],</span> <span class="p">[])</span>
</pre></div>
</div>
</li>
</ul>
</div>
<div class="section" id="security-considerations">
<span id="ssl-security"></span><h2>17.3.7. Security considerations<a class="headerlink" href="#security-considerations" title="Permalink to this headline">¶</a></h2>
<div class="section" id="best-defaults">
<h3>17.3.7.1. Best defaults<a class="headerlink" href="#best-defaults" title="Permalink to this headline">¶</a></h3>
<p>For <strong>client use</strong>, if you don’t have any special requirements for your
security policy, it is highly recommended that you use the
<a class="reference internal" href="#ssl.create_default_context" title="ssl.create_default_context"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_default_context()</span></code></a> function to create your SSL context.
It will load the system’s trusted CA certificates, enable certificate
validation and hostname checking, and try to choose reasonably secure
protocol and cipher settings.</p>
<p>If a client certificate is needed for the connection, it can be added with
<a class="reference internal" href="#ssl.SSLContext.load_cert_chain" title="ssl.SSLContext.load_cert_chain"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.load_cert_chain()</span></code></a>.</p>
<p>By contrast, if you create the SSL context by calling the <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a>
constructor yourself, it will not have certificate validation nor hostname
checking enabled by default. If you do so, please read the paragraphs below
to achieve a good security level.</p>
</div>
<div class="section" id="manual-settings">
<h3>17.3.7.2. Manual settings<a class="headerlink" href="#manual-settings" title="Permalink to this headline">¶</a></h3>
<div class="section" id="verifying-certificates">
<h4>17.3.7.2.1. Verifying certificates<a class="headerlink" href="#verifying-certificates" title="Permalink to this headline">¶</a></h4>
<p>When calling the <a class="reference internal" href="#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">SSLContext</span></code></a> constructor directly,
<a class="reference internal" href="#ssl.CERT_NONE" title="ssl.CERT_NONE"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_NONE</span></code></a> is the default. Since it does not authenticate the other
peer, it can be insecure, especially in client mode where most of time you
would like to ensure the authenticity of the server you’re talking to.
Therefore, when in client mode, it is highly recommended to use
<a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a>. However, it is in itself not sufficient; you also
have to check that the server certificate, which can be obtained by calling
<a class="reference internal" href="#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.getpeercert()</span></code></a>, matches the desired service. For many
protocols and applications, the service can be identified by the hostname;
in this case, the <a class="reference internal" href="#ssl.match_hostname" title="ssl.match_hostname"><code class="xref py py-func docutils literal notranslate"><span class="pre">match_hostname()</span></code></a> function can be used. This common
check is automatically performed when <a class="reference internal" href="#ssl.SSLContext.check_hostname" title="ssl.SSLContext.check_hostname"><code class="xref py py-attr docutils literal notranslate"><span class="pre">SSLContext.check_hostname</span></code></a> is
enabled.</p>
<p>In server mode, if you want to authenticate your clients using the SSL layer
(rather than using a higher-level authentication mechanism), you’ll also have
to specify <a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a> and similarly check the client certificate.</p>
<blockquote>
<div><div class="admonition note">
<p class="admonition-title">Note</p>
<p>In client mode, <a class="reference internal" href="#ssl.CERT_OPTIONAL" title="ssl.CERT_OPTIONAL"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_OPTIONAL</span></code></a> and <a class="reference internal" href="#ssl.CERT_REQUIRED" title="ssl.CERT_REQUIRED"><code class="xref py py-const docutils literal notranslate"><span class="pre">CERT_REQUIRED</span></code></a> are
equivalent unless anonymous ciphers are enabled (they are disabled
by default).</p>
</div>
</div></blockquote>
</div>
<div class="section" id="protocol-versions">
<h4>17.3.7.2.2. Protocol versions<a class="headerlink" href="#protocol-versions" title="Permalink to this headline">¶</a></h4>
<p>SSL versions 2 and 3 are considered insecure and are therefore dangerous to
use. If you want maximum compatibility between clients and servers, it is
recommended to use <a class="reference internal" href="#ssl.PROTOCOL_SSLv23" title="ssl.PROTOCOL_SSLv23"><code class="xref py py-const docutils literal notranslate"><span class="pre">PROTOCOL_SSLv23</span></code></a> as the protocol version and then
disable SSLv2 and SSLv3 explicitly using the <a class="reference internal" href="#ssl.SSLContext.options" title="ssl.SSLContext.options"><code class="xref py py-data docutils literal notranslate"><span class="pre">SSLContext.options</span></code></a>
attribute:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">context</span> <span class="o">=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">SSLContext</span><span class="p">(</span><span class="n">ssl</span><span class="o">.</span><span class="n">PROTOCOL_SSLv23</span><span class="p">)</span>
<span class="n">context</span><span class="o">.</span><span class="n">options</span> <span class="o">|=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">OP_NO_SSLv2</span>
<span class="n">context</span><span class="o">.</span><span class="n">options</span> <span class="o">|=</span> <span class="n">ssl</span><span class="o">.</span><span class="n">OP_NO_SSLv3</span>
</pre></div>
</div>
<p>The SSL context created above will only allow TLSv1 and later (if
supported by your system) connections.</p>
</div>
<div class="section" id="cipher-selection">
<h4>17.3.7.2.3. Cipher selection<a class="headerlink" href="#cipher-selection" title="Permalink to this headline">¶</a></h4>
<p>If you have advanced security requirements, fine-tuning of the ciphers
enabled when negotiating a SSL session is possible through the
<a class="reference internal" href="#ssl.SSLContext.set_ciphers" title="ssl.SSLContext.set_ciphers"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_ciphers()</span></code></a> method. Starting from Python 2.7.9, the
ssl module disables certain weak ciphers by default, but you may want
to further restrict the cipher choice. Be sure to read OpenSSL’s documentation
about the <a class="reference external" href="https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT">cipher list format</a>.
If you want to check which ciphers are enabled by a given cipher list, use the
<code class="docutils literal notranslate"><span class="pre">openssl</span> <span class="pre">ciphers</span></code> command on your system.</p>
</div>
</div>
<div class="section" id="multi-processing">
<h3>17.3.7.3. Multi-processing<a class="headerlink" href="#multi-processing" title="Permalink to this headline">¶</a></h3>
<p>If using this module as part of a multi-processed application (using,
for example the <a class="reference internal" href="multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based "threading" interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">multiprocessing</span></code></a> or <code class="xref py py-mod docutils literal notranslate"><span class="pre">concurrent.futures</span></code> modules),
be aware that OpenSSL’s internal random number generator does not properly
handle forked processes. Applications must change the PRNG state of the
parent process if they use any SSL feature with <a class="reference internal" href="os.html#os.fork" title="os.fork"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.fork()</span></code></a>. Any
successful call of <a class="reference internal" href="#ssl.RAND_add" title="ssl.RAND_add"><code class="xref py py-func docutils literal notranslate"><span class="pre">RAND_add()</span></code></a>, <code class="xref py py-func docutils literal notranslate"><span class="pre">RAND_bytes()</span></code> or
<code class="xref py py-func docutils literal notranslate"><span class="pre">RAND_pseudo_bytes()</span></code> is sufficient.</p>
</div>
</div>
<div class="section" id="libressl-support">
<h2>17.3.8. LibreSSL support<a class="headerlink" href="#libressl-support" title="Permalink to this headline">¶</a></h2>
<p>LibreSSL is a fork of OpenSSL 1.0.1. The ssl module has limited support for
LibreSSL. Some features are not available when the ssl module is compiled
with LibreSSL.</p>
<ul class="simple">
<li><p>LibreSSL >= 2.6.1 no longer supports NPN. The methods
<a class="reference internal" href="#ssl.SSLContext.set_npn_protocols" title="ssl.SSLContext.set_npn_protocols"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_npn_protocols()</span></code></a> and
<a class="reference internal" href="#ssl.SSLSocket.selected_npn_protocol" title="ssl.SSLSocket.selected_npn_protocol"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLSocket.selected_npn_protocol()</span></code></a> are not available.</p></li>
<li><p><a class="reference internal" href="#ssl.SSLContext.set_default_verify_paths" title="ssl.SSLContext.set_default_verify_paths"><code class="xref py py-meth docutils literal notranslate"><span class="pre">SSLContext.set_default_verify_paths()</span></code></a> ignores the env vars
<span class="target" id="index-18"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">SSL_CERT_FILE</span></code> and <span class="target" id="index-19"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">SSL_CERT_PATH</span></code> although
<a class="reference internal" href="#ssl.get_default_verify_paths" title="ssl.get_default_verify_paths"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_default_verify_paths()</span></code></a> still reports them.</p></li>
</ul>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt>Class <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate"><span class="pre">socket.socket</span></code></a></dt><dd><p>Documentation of underlying <a class="reference internal" href="socket.html#module-socket" title="socket: Low-level networking interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code></a> class</p>
</dd>
<dt><a class="reference external" href="https://httpd.apache.org/docs/trunk/en/ssl/ssl_intro.html">SSL/TLS Strong Encryption: An Introduction</a></dt><dd><p>Intro from the Apache webserver documentation</p>
</dd>
<dt><a class="reference external" href="https://www.ietf.org/rfc/rfc1422">RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management</a></dt><dd><p>Steve Kent</p>
</dd>
<dt><a class="reference external" href="https://www.ietf.org/rfc/rfc1750">RFC 1750: Randomness Recommendations for Security</a></dt><dd><p>D. Eastlake et. al.</p>
</dd>
<dt><a class="reference external" href="https://www.ietf.org/rfc/rfc3280">RFC 3280: Internet X.509 Public Key Infrastructure Certificate and CRL Profile</a></dt><dd><p>Housley et. al.</p>
</dd>
<dt><a class="reference external" href="https://www.ietf.org/rfc/rfc4366">RFC 4366: Transport Layer Security (TLS) Extensions</a></dt><dd><p>Blake-Wilson et. al.</p>
</dd>
<dt><a class="reference external" href="https://tools.ietf.org/html/rfc5246">RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2</a></dt><dd><p>T. Dierks et. al.</p>
</dd>
<dt><a class="reference external" href="https://tools.ietf.org/html/rfc6066">RFC 6066: Transport Layer Security (TLS) Extensions</a></dt><dd><p>D. Eastlake</p>
</dd>
<dt><a class="reference external" href="https://www.iana.org/assignments/tls-parameters/tls-parameters.xml">IANA TLS: Transport Layer Security (TLS) Parameters</a></dt><dd><p>IANA</p>
</dd>
<dt><a class="reference external" href="https://tools.ietf.org/html/rfc7525">RFC 7525: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)</a></dt><dd><p>IETF</p>
</dd>
<dt><a class="reference external" href="https://wiki.mozilla.org/Security/Server_Side_TLS">Mozilla’s Server Side TLS recommendations</a></dt><dd><p>Mozilla</p>
</dd>
</dl>
</div>
</div>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">17.3. <code class="xref py py-mod docutils literal notranslate"><span class="pre">ssl</span></code> — TLS/SSL wrapper for socket objects</a><ul>
<li><a class="reference internal" href="#functions-constants-and-exceptions">17.3.1. Functions, Constants, and Exceptions</a><ul>
<li><a class="reference internal" href="#socket-creation">17.3.1.1. Socket creation</a></li>
<li><a class="reference internal" href="#context-creation">17.3.1.2. Context creation</a></li>
<li><a class="reference internal" href="#random-generation">17.3.1.3. Random generation</a></li>
<li><a class="reference internal" href="#certificate-handling">17.3.1.4. Certificate handling</a></li>
<li><a class="reference internal" href="#constants">17.3.1.5. Constants</a></li>
</ul>
</li>
<li><a class="reference internal" href="#ssl-sockets">17.3.2. SSL Sockets</a></li>
<li><a class="reference internal" href="#ssl-contexts">17.3.3. SSL Contexts</a></li>
<li><a class="reference internal" href="#certificates">17.3.4. Certificates</a><ul>
<li><a class="reference internal" href="#certificate-chains">17.3.4.1. Certificate chains</a></li>
<li><a class="reference internal" href="#ca-certificates">17.3.4.2. CA certificates</a></li>
<li><a class="reference internal" href="#combined-key-and-certificate">17.3.4.3. Combined key and certificate</a></li>
<li><a class="reference internal" href="#self-signed-certificates">17.3.4.4. Self-signed certificates</a></li>
</ul>
</li>
<li><a class="reference internal" href="#examples">17.3.5. Examples</a><ul>
<li><a class="reference internal" href="#testing-for-ssl-support">17.3.5.1. Testing for SSL support</a></li>
<li><a class="reference internal" href="#client-side-operation">17.3.5.2. Client-side operation</a></li>
<li><a class="reference internal" href="#server-side-operation">17.3.5.3. Server-side operation</a></li>
</ul>
</li>
<li><a class="reference internal" href="#notes-on-non-blocking-sockets">17.3.6. Notes on non-blocking sockets</a></li>
<li><a class="reference internal" href="#security-considerations">17.3.7. Security considerations</a><ul>
<li><a class="reference internal" href="#best-defaults">17.3.7.1. Best defaults</a></li>
<li><a class="reference internal" href="#manual-settings">17.3.7.2. Manual settings</a><ul>
<li><a class="reference internal" href="#verifying-certificates">17.3.7.2.1. Verifying certificates</a></li>
<li><a class="reference internal" href="#protocol-versions">17.3.7.2.2. Protocol versions</a></li>
<li><a class="reference internal" href="#cipher-selection">17.3.7.2.3. Cipher selection</a></li>
</ul>
</li>
<li><a class="reference internal" href="#multi-processing">17.3.7.3. Multi-processing</a></li>
</ul>
</li>
<li><a class="reference internal" href="#libressl-support">17.3.8. LibreSSL support</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="socket.html"
title="previous chapter">17.2. <code class="xref py py-mod docutils literal notranslate"><span class="pre">socket</span></code> — Low-level networking interface</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="signal.html"
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