php-doc-en/reference/mcrypt/functions/mcrypt-get-iv-size.xml
Derick Rethans a317e27ddb - Another note ntegration
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2003-04-25 19:04:43 +00:00

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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.7 $ -->
<!-- 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
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>
<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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