mcrypt-create-iv.xml

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<refentry xml:id="function.mcrypt-create-iv" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>mcrypt_create_iv</refname>
  <refpurpose>Creates an initialization vector (IV) from a random source</refpurpose>
 </refnamediv>
 
 <refsynopsisdiv>
  <warning>
   &warn.deprecated.function.7-1-0.removed.7-2-0.alternatives;
   <simplelist role="alternatives">
    <member><function>random_bytes</function></member>
   </simplelist>
  </warning>
 </refsynopsisdiv>
 
 <refsect1 role="description">
  &reftitle.description;
  <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><initializer>MCRYPT_DEV_URANDOM</initializer></methodparam>
  </methodsynopsis>
  <para>
   Creates an initialization vector (IV) from a random source.
  </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
   losing security.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>size</parameter></term>
     <listitem>
      <para>
       The size of the IV.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>source</parameter></term>
     <listitem>
      <para>
       The source of the IV. 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>). Prior to 5.3.0,
       <constant>MCRYPT_RAND</constant> was the only one supported on Windows.
      </para>
      <para>
       Note that the default value of this parameter was
       <constant>MCRYPT_DEV_RANDOM</constant> prior to PHP 5.6.0.
      </para>
      <note>
       <simpara>
        Note that <constant>MCRYPT_DEV_RANDOM</constant> may block until more
        entropy is available.
       </simpara>
      </note>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the initialization vector, or &false; on error.
  </para>
 </refsect1>
 
 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>5.6.0</entry>
       <entry>
        <constant>MCRYPT_DEV_URANDOM</constant> is now the default value of
        <parameter>source</parameter>.
       </entry>
      </row>
      <row>
       <entry>5.3.0</entry>
       <entry>
        <constant>MCRYPT_DEV_RANDOM</constant> and
        <constant>MCRYPT_DEV_URANDOM</constant> became available on Windows
        platforms.
       </entry>
      </row>
      <row>
       <entry>5.3.0</entry>
       <entry>
        It is no longer required to call <function>srand</function> first. This
        is now done automatically.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <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>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><link xlink:href="&url.mcrypt.iv;">&url.mcrypt.iv;</link></member>
    <member><link xlink:href="&url.mcrypt.bcm;">&url.mcrypt.bcm;</link></member>
    <member>Chapter 9.3 of &book.applied.cryptography;</member>
    <member><function>random_bytes</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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