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<title>Generates cryptographically secure pseudo-random bytes</title>
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<div class="refnamediv">
<h1 class="refname">random_bytes</h1>
<p class="verinfo">(PHP 7)</p><p class="refpurpose"><span class="refname">random_bytes</span> — <span class="dc-title">Generates cryptographically secure pseudo-random bytes</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.random-bytes-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">string</span> <span class="methodname"><strong>random_bytes</strong></span>
( <span class="methodparam"><span class="type">int</span> <code class="parameter">$length</code></span>
)</div>
<p class="para rdfs-comment">
Generates an arbitrary length string of cryptographic random bytes that are
suitable for cryptographic use, such as when generating salts, keys or
initialization vectors.
</p>
<p class="para">
The sources of randomness used for this function are as follows:
</p>
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
On Windows,
<a href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa379942(v=vs.85).aspx" class="link external">» <span class="function"><strong>CryptGenRandom()</strong></span></a>
will always be used.
</span>
</li>
<li class="listitem">
<span class="simpara">
On Linux, the
<a href="http://man7.org/linux/man-pages/man2/getrandom.2.html" class="link external">» getrandom(2)</a>
syscall will be used if available.
</span>
</li>
<li class="listitem">
<span class="simpara">
On other platforms, <var class="filename">/dev/urandom</var> will be used.
</span>
</li>
<li class="listitem">
<span class="simpara">
If none of the aforementioned sources are available, then an
<a href="class.exception.html" class="classname">Exception</a> will be thrown.
</span>
</li>
</ul>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
Although this function was added to PHP in PHP 7.0, a
<a href="https://github.com/paragonie/random_compat" class="link external">» userland implementation</a>
is available for PHP 5.2 to 5.6, inclusive.
</span>
</p></blockquote>
</div>
<div class="refsect1 parameters" id="refsect1-function.random-bytes-parameters">
<h3 class="title">Parameters</h3>
<dl>
<dt>
<code class="parameter">length</code></dt>
<dd>
<p class="para">
The length of the random string that should be returned in bytes.
</p>
</dd>
</dl>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.random-bytes-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns a string containing the requested number of cryptographically
secure random bytes.
</p>
</div>
<div class="refsect1 errors" id="refsect1-function.random-bytes-errors">
<h3 class="title">Errors/Exceptions</h3>
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
If an appropriate source of randomness cannot be found,
an <a href="class.exception.html" class="classname">Exception</a> will be thrown.
</span>
</li>
<li class="listitem">
<span class="simpara">
If invalid parameters are given, a <a href="class.typeerror.html" class="classname">TypeError</a>
will be thrown.
</span>
</li>
<li class="listitem">
<span class="simpara">
If an invalid <code class="parameter">length</code> of bytes is given, an
<a href="class.error.html" class="classname">Error</a> will be thrown.
</span>
</li>
</ul>
</div>
<div class="refsect1 examples" id="refsect1-function.random-bytes-examples">
<h3 class="title">Examples</h3>
<div class="example" id="example-919">
<p><strong>Example #1 <span class="function"><strong>random_bytes()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$bytes </span><span style="color: #007700">= </span><span style="color: #0000BB">random_bytes</span><span style="color: #007700">(</span><span style="color: #0000BB">5</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">bin2hex</span><span style="color: #007700">(</span><span style="color: #0000BB">$bytes</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output
something similar to:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
string(10) "385e33f741"
</pre></div>
</div>
</div>
</div>
<div class="refsect1 seealso" id="refsect1-function.random-bytes-seealso">
<h3 class="title">See Also</h3>
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.random-int.html" class="function" rel="rdfs-seeAlso">random_int()</a> - Generates cryptographically secure pseudo-random integers</span></li>
<li class="member"><span class="function"><a href="function.openssl-random-pseudo-bytes.html" class="function" rel="rdfs-seeAlso">openssl_random_pseudo_bytes()</a> - Generate a pseudo-random string of bytes</span></li>
<li class="member"><span class="function"><a href="function.bin2hex.html" class="function" rel="rdfs-seeAlso">bin2hex()</a> - Convert binary data into hexadecimal representation</span></li>
</ul>
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