php-doc-en/reference/mcrypt/functions/mcrypt-get-iv-size.xml

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<!-- $Revision: 1.6 $ -->
<!-- splitted from ./en/functions/mcrypt.xml, last change in rev 1.7 -->
  <refentry id="function.mcrypt-get-iv-size">
   <refnamediv>
    <refname>mcrypt_get_iv_size</refname>
    <refpurpose>
     Returns the size of the IV belonging to a specific cipher/mode combination
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>int</type><methodname>mcrypt_get_iv_size</methodname>
      <methodparam><type>resource</type><parameter>td</parameter></methodparam>
     </methodsynopsis>
     <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>
     The first prototype is when linked against libmcrypt 2.2.x, the
     second when linked against libmcrypt 2.4.x or higher.
    </para>
    <para>
     <function>mcrypt_get_iv_size</function> 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>
    <para>
     <parameter>cipher</parameter> is one of the MCRYPT_ciphername
     constants of the name of the algorithm as string.
    </para>
    <para>
     <parameter>mode</parameter> is one of the MCRYPT_MODE_modename
     constants of one of "ecb", "cbc", "cfb", "ofb", "nofb" or 
     "stream".
    </para>
    <para>
     <parameter>td</parameter> is the resource that is returned by
     <function>mcrypt_module_open</function>.
    </para>
    <para>
     <example>
      <title><function>mcrypt_create_iv</function> example</title>
      <programlisting role="php">
<![CDATA[
<?php
    $size = mcrypt_get_iv_size (MCRYPT_CAST_256, MCRYPT_MODE_CFB);

    $size = mcrypt_get_iv_size ('des', 'ecb');
?>
]]>
      </programlisting>
     </example>
    </para>
    <para>
     See also 
     <function>mcrypt_get_block_size</function>, and
     <function>mcrypt_create_iv</function>.
    </para>
   </refsect1>
  </refentry>

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