<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.8 $ -->
<!-- splitted from ./en/functions/mcrypt.xml, last change in rev 1.2 -->
  <refentry id="function.mcrypt-create-iv">
   <refnamediv>
    <refname>mcrypt_create_iv</refname>
    <refpurpose>
     Create an initialization vector (IV) from a random source
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>string</type><methodname>mcrypt_create_iv</methodname>
      <methodparam><type>int</type><parameter>size</parameter></methodparam>
      <methodparam choice="opt"><type>int</type><parameter>source</parameter></methodparam>
     </methodsynopsis>
    <para>
     <function>mcrypt_create_iv</function> is used to create an IV.
    </para>
    <para>
     Parameter
     <parameter>size</parameter> determines the size of the IV,
     parameter <parameter>source</parameter> (defaults to random value)
     specifies the source of the IV.
    </para>
    <para>
     The source can be <constant>MCRYPT_RAND</constant> (system random
     number generator), <constant>MCRYPT_DEV_RANDOM</constant> (read
     data from <filename>/dev/random</filename>) and
     <constant>MCRYPT_DEV_URANDOM</constant> (read data from
     <filename>/dev/urandom</filename>). <constant>MCRYPT_RAND</constant>
     is the only one supported on Windows because Windows (of course)
     doesn't have <filename>/dev/random</filename> or
     <filename>/dev/urandom</filename>.
    </para>
    <note>
     <para>
      When using <constant>MCRYPT_RAND</constant>, remember to call
      <function>srand</function> before
      <function>mcrypt_create_iv</function> to initialize the random
      number generator; it is not seeded automatically like
      <function>rand</function> is.
     </para>
    </note>
    <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);
    $iv = mcrypt_create_iv($size, MCRYPT_DEV_RANDOM);
?>
]]>
      </programlisting>
     </example>
    </para>
    <para>
     The IV is only meant to give an alternative seed to the encryption
     routines. This IV does not need to be secret at all, though it can be
     desirable. You even can send it along with your ciphertext without
     loosing security.
    </para>
    <para>
     More information can be found at <ulink
     url="&url.mcrypt.iv;">&url.mcrypt.iv;</ulink>, <ulink
     url="&url.mcrypt.bcm;">&url.mcrypt.bcm;</ulink> and in chapter 9.3 of
     Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a discussion of
     this topic.
    </para>
   </refsect1>
  </refentry>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"../../../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->