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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 297028 $ -->
<refentry xml:id="function.mcrypt-get-iv-size" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>mcrypt_get_iv_size</refname>
<refpurpose>Returns the size of the IV belonging to a specific cipher/mode combination</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>int</type><methodname>mcrypt_get_iv_size</methodname>
<methodparam><type>string</type><parameter>cipher</parameter></methodparam>
<methodparam><type>string</type><parameter>mode</parameter></methodparam>
</methodsynopsis>
<para>
Gets the size of the IV belonging to a specific
<parameter>cipher</parameter>/<parameter>mode</parameter> combination.
</para>
<para>
It is more useful to use the <function>mcrypt_enc_get_iv_size</function>
function as this uses the resource returned by
<function>mcrypt_module_open</function>.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>cipher</parameter></term>
<listitem>
<para>
One of the <literal>MCRYPT_ciphername</literal> constants of the name
of the algorithm as string.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>mode</parameter></term>
<listitem>
<para>
<parameter>mode</parameter> is one of the MCRYPT_MODE_modename constants
or one of "ecb", "cbc", "cfb", "ofb", "nofb" or "stream". 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.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Returns the size of the Initialisation Vector (IV) in bytes. On error the
function returns &false;. If the IV is ignored in the specified cipher/mode
combination zero is returned.
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>mcrypt_get_iv_size</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
echo mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB) . "\n";
echo mcrypt_get_iv_size('des', 'ecb') . "\n";
?>
]]>
</programlisting>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>mcrypt_get_block_size</function></member>
<member><function>mcrypt_enc_get_iv_size</function></member>
<member><function>mcrypt_create_iv</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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