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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@166167 c90b9560-bf6c-de11-be94-00142212c4b1
94 lines
3.1 KiB
XML
94 lines
3.1 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.8 $ -->
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<!-- splitted from ./en/functions/mcrypt.xml, last change in rev 1.2 -->
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<refentry id="function.mcrypt-create-iv">
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<refnamediv>
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<refname>mcrypt_create_iv</refname>
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<refpurpose>
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Create an initialization vector (IV) from a random source
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</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<methodsynopsis>
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<type>string</type><methodname>mcrypt_create_iv</methodname>
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<methodparam><type>int</type><parameter>size</parameter></methodparam>
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<methodparam choice="opt"><type>int</type><parameter>source</parameter></methodparam>
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</methodsynopsis>
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<para>
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<function>mcrypt_create_iv</function> is used to create an IV.
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</para>
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<para>
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Parameter
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<parameter>size</parameter> determines the size of the IV,
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parameter <parameter>source</parameter> (defaults to random value)
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specifies the source of the IV.
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</para>
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<para>
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The source can be <constant>MCRYPT_RAND</constant> (system random
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number generator), <constant>MCRYPT_DEV_RANDOM</constant> (read
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data from <filename>/dev/random</filename>) and
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<constant>MCRYPT_DEV_URANDOM</constant> (read data from
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<filename>/dev/urandom</filename>). <constant>MCRYPT_RAND</constant>
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is the only one supported on Windows because Windows (of course)
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doesn't have <filename>/dev/random</filename> or
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<filename>/dev/urandom</filename>.
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</para>
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<note>
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<para>
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When using <constant>MCRYPT_RAND</constant>, remember to call
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<function>srand</function> before
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<function>mcrypt_create_iv</function> to initialize the random
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number generator; it is not seeded automatically like
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<function>rand</function> is.
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</para>
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</note>
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<para>
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<example>
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<title><function>mcrypt_create_iv</function> example</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$size = mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB);
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$iv = mcrypt_create_iv($size, MCRYPT_DEV_RANDOM);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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The IV is only meant to give an alternative seed to the encryption
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routines. This IV does not need to be secret at all, though it can be
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desirable. You even can send it along with your ciphertext without
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loosing security.
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</para>
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<para>
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More information can be found at <ulink
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url="&url.mcrypt.iv;">&url.mcrypt.iv;</ulink>, <ulink
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url="&url.mcrypt.bcm;">&url.mcrypt.bcm;</ulink> and in chapter 9.3 of
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Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a discussion of
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this topic.
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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