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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>20.5. Password Authentication</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="auth-trust.html" title="20.4. Trust Authentication" /><link rel="next" href="gssapi-auth.html" title="20.6. GSSAPI Authentication" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">20.5. Password Authentication</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="auth-trust.html" title="20.4. Trust Authentication">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="client-authentication.html" title="Chapter 20. Client Authentication">Up</a></td><th width="60%" align="center">Chapter 20. Client Authentication</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="gssapi-auth.html" title="20.6. GSSAPI Authentication">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="AUTH-PASSWORD"><div class="titlepage"><div><div><h2 class="title" style="clear: both">20.5. Password Authentication</h2></div></div></div><a id="id-1.6.7.12.2" class="indexterm"></a><a id="id-1.6.7.12.3" class="indexterm"></a><a id="id-1.6.7.12.4" class="indexterm"></a><p>
There are several password-based authentication methods. These methods
operate similarly but differ in how the users' passwords are stored on the
server and how the password provided by a client is sent across the
connection.
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">scram-sha-256</code></span></dt><dd><p>
The method <code class="literal">scram-sha-256</code> performs SCRAM-SHA-256
authentication, as described in
<a class="ulink" href="https://tools.ietf.org/html/rfc7677" target="_top">RFC 7677</a>. It
is a challenge-response scheme that prevents password sniffing on
untrusted connections and supports storing passwords on the server in a
cryptographically hashed form that is thought to be secure.
</p><p>
This is the most secure of the currently provided methods, but it is
not supported by older client libraries.
</p></dd><dt><span class="term"><code class="literal">md5</code></span></dt><dd><p>
The method <code class="literal">md5</code> uses a custom less secure challenge-response
mechanism. It prevents password sniffing and avoids storing passwords
on the server in plain text but provides no protection if an attacker
manages to steal the password hash from the server. Also, the MD5 hash
algorithm is nowadays no longer considered secure against determined
attacks.
</p><p>
The <code class="literal">md5</code> method cannot be used with
the <a class="xref" href="runtime-config-connection.html#GUC-DB-USER-NAMESPACE">db_user_namespace</a> feature.
</p><p>
To ease transition from the <code class="literal">md5</code> method to the newer
SCRAM method, if <code class="literal">md5</code> is specified as a method
in <code class="filename">pg_hba.conf</code> but the user's password on the
server is encrypted for SCRAM (see below), then SCRAM-based
authentication will automatically be chosen instead.
</p></dd><dt><span class="term"><code class="literal">password</code></span></dt><dd><p>
The method <code class="literal">password</code> sends the password in clear-text and is
therefore vulnerable to password <span class="quote">“<span class="quote">sniffing</span>”</span> attacks. It should
always be avoided if possible. If the connection is protected by SSL
encryption then <code class="literal">password</code> can be used safely, though.
(Though SSL certificate authentication might be a better choice if one
is depending on using SSL).
</p></dd></dl></div><p>
<span class="productname">PostgreSQL</span> database passwords are
separate from operating system user passwords. The password for
each database user is stored in the <code class="literal">pg_authid</code> system
catalog. Passwords can be managed with the SQL commands
<a class="xref" href="sql-createrole.html" title="CREATE ROLE"><span class="refentrytitle">CREATE ROLE</span></a> and
<a class="xref" href="sql-alterrole.html" title="ALTER ROLE"><span class="refentrytitle">ALTER ROLE</span></a>,
e.g., <strong class="userinput"><code>CREATE ROLE foo WITH LOGIN PASSWORD 'secret'</code></strong>,
or the <span class="application">psql</span>
command <code class="literal">\password</code>.
If no password has been set up for a user, the stored password
is null and password authentication will always fail for that user.
</p><p>
The availability of the different password-based authentication methods
depends on how a user's password on the server is encrypted (or hashed,
more accurately). This is controlled by the configuration
parameter <a class="xref" href="runtime-config-connection.html#GUC-PASSWORD-ENCRYPTION">password_encryption</a> at the time the
password is set. If a password was encrypted using
the <code class="literal">scram-sha-256</code> setting, then it can be used for the
authentication methods <code class="literal">scram-sha-256</code>
and <code class="literal">password</code> (but password transmission will be in
plain text in the latter case). The authentication method
specification <code class="literal">md5</code> will automatically switch to using
the <code class="literal">scram-sha-256</code> method in this case, as explained
above, so it will also work. If a password was encrypted using
the <code class="literal">md5</code> setting, then it can be used only for
the <code class="literal">md5</code> and <code class="literal">password</code> authentication
method specifications (again, with the password transmitted in plain text
in the latter case). (Previous PostgreSQL releases supported storing the
password on the server in plain text. This is no longer possible.) To
check the currently stored password hashes, see the system
catalog <code class="literal">pg_authid</code>.
</p><p>
To upgrade an existing installation from <code class="literal">md5</code>
to <code class="literal">scram-sha-256</code>, after having ensured that all client
libraries in use are new enough to support SCRAM,
set <code class="literal">password_encryption = 'scram-sha-256'</code>
in <code class="filename">postgresql.conf</code>, make all users set new passwords,
and change the authentication method specifications
in <code class="filename">pg_hba.conf</code> to <code class="literal">scram-sha-256</code>.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="auth-trust.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="client-authentication.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="gssapi-auth.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">20.4. Trust Authentication </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 20.6. GSSAPI Authentication</td></tr></table></div></body></html>
