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<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 <constant>MCRYPT_ciphername</constant> constants, or the name
       of the algorithm as string.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>mode</parameter></term>
     <listitem>
      <para>
       One of the <constant>MCRYPT_MODE_modename</constant> constants, or one of
       the following strings: "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 Initialization 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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