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<title>Returns the size of the IV belonging to a specific cipher/mode combination</title>
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<div class="refnamediv">
<h1 class="refname">mcrypt_get_iv_size</h1>
<p class="verinfo">(PHP 4 >= 4.0.2, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0)</p><p class="refpurpose"><span class="refname">mcrypt_get_iv_size</span> — <span class="dc-title">Returns the size of the IV belonging to a specific cipher/mode combination</span></p>
</div>
<div id="function.mcrypt-get-iv-size-refsynopsisdiv">
<div class="warning"><strong class="warning">Warning</strong><p class="simpara">This function has been
<em class="emphasis">DEPRECATED</em> as of PHP 7.1.0. Relying on this function
is highly discouraged.</p></div>
</div>
<div class="refsect1 description" id="refsect1-function.mcrypt-get-iv-size-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">int</span> <span class="methodname"><strong>mcrypt_get_iv_size</strong></span>
( <span class="methodparam"><span class="type">string</span> <code class="parameter">$cipher</code></span>
, <span class="methodparam"><span class="type">string</span> <code class="parameter">$mode</code></span>
)</div>
<p class="para rdfs-comment">
Gets the size of the IV belonging to a specific
<code class="parameter">cipher</code>/<code class="parameter">mode</code> combination.
</p>
<p class="para">
It is more useful to use the <span class="function"><a href="function.mcrypt-enc-get-iv-size.html" class="function">mcrypt_enc_get_iv_size()</a></span>
function as this uses the resource returned by
<span class="function"><a href="function.mcrypt-module-open.html" class="function">mcrypt_module_open()</a></span>.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.mcrypt-get-iv-size-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">cipher</code></dt>
<dd>
<p class="para">One of the <strong><code>MCRYPT_ciphername</code></strong> constants, or the name of the algorithm as string.</p>
</dd>
<dt>
<code class="parameter">mode</code></dt>
<dd>
<p class="para">One of the <strong><code>MCRYPT_MODE_modename</code></strong> constants, or one of the following strings: "ecb", "cbc", "cfb", "ofb", "nofb" or "stream".</p>
<p class="para">
The IV is ignored in ECB mode as this mode does not require it. You will
need to have the same IV (think: starting point) both at encryption and
decryption stages, otherwise your encryption will fail.
</p>
</dd>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.mcrypt-get-iv-size-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns the size of the Initialization Vector (IV) in bytes. On error the
function returns <strong><code>FALSE</code></strong>. If the IV is ignored in the specified cipher/mode
combination zero is returned.
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.mcrypt-get-iv-size-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-943">
<p><strong>Example #1 <span class="function"><strong>mcrypt_get_iv_size()</strong></span> Example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /> </span><span style="color: #007700">echo </span><span style="color: #0000BB">mcrypt_get_iv_size</span><span style="color: #007700">(</span><span style="color: #0000BB">MCRYPT_CAST_256</span><span style="color: #007700">, </span><span style="color: #0000BB">MCRYPT_MODE_CFB</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br /> echo </span><span style="color: #0000BB">mcrypt_get_iv_size</span><span style="color: #007700">(</span><span style="color: #DD0000">'des'</span><span style="color: #007700">, </span><span style="color: #DD0000">'ecb'</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.mcrypt-get-iv-size-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.mcrypt-get-block-size.html" class="function" rel="rdfs-seeAlso">mcrypt_get_block_size()</a> - Gets the block size of the specified cipher</span></li>
<li class="member"><span class="function"><a href="function.mcrypt-enc-get-iv-size.html" class="function" rel="rdfs-seeAlso">mcrypt_enc_get_iv_size()</a> - Returns the size of the IV of the opened algorithm</span></li>
<li class="member"><span class="function"><a href="function.mcrypt-create-iv.html" class="function" rel="rdfs-seeAlso">mcrypt_create_iv()</a> - Creates an initialization vector (IV) from a random source</span></li>
</ul>
</p>
</div>
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