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>mcrypt_create_iv</H1
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><P
>    (PHP 3&#62;= 3.0.8, PHP 4 , PHP 5)</P
>mcrypt_create_iv&nbsp;--&nbsp;
     Create an initialization vector (IV) from a random source
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><H2
>Description</H2
>string <B
CLASS="methodname"
>mcrypt_create_iv</B
> ( int size, int source)<BR
></BR
><P
>&#13;     <B
CLASS="function"
>mcrypt_create_iv()</B
> is used to create an IV.
    </P
><P
>&#13;     <B
CLASS="function"
>mcrypt_create_iv()</B
> takes two arguments,
     <VAR
CLASS="parameter"
>size</VAR
> determines the size of the IV,
     <VAR
CLASS="parameter"
>source</VAR
> specifies the source of the IV.
    </P
><P
>&#13;     The source can be MCRYPT_RAND (system random number generator),
     MCRYPT_DEV_RANDOM (read data from /dev/random) and
     MCRYPT_DEV_URANDOM (read data from /dev/urandom). If you use
     MCRYPT_RAND, make sure to call srand() before to initialize the
     random number generator. MCRYPT_RAND is the only one supported on Windows
     because Windows (of course) doesn't have /dev/random or /dev/urandom.
    </P
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><B
>Exemplu 1. <B
CLASS="function"
>mcrypt_create_iv()</B
> example</B
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><code><font color="#000000">
<font color="#0000BB">&lt;?php<br />&nbsp;&nbsp;&nbsp;&nbsp;$size </font><font color="#007700">= </font><font color="#0000BB">mcrypt_get_iv_size</font><font color="#007700">(</font><font color="#0000BB">MCRYPT_CAST_256</font><font color="#007700">, </font><font color="#0000BB">MCRYPT_MODE_CFB</font><font color="#007700">);<br />&nbsp;&nbsp;&nbsp;&nbsp;</font><font color="#0000BB">$iv </font><font color="#007700">= </font><font color="#0000BB">mcrypt_create_iv</font><font color="#007700">(</font><font color="#0000BB">$size</font><font color="#007700">, </font><font color="#0000BB">MCRYPT_DEV_RANDOM</font><font color="#007700">);<br /></font><font color="#0000BB">?&gt;</font>
</font>
</code></TD
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>
    </P
><P
>&#13;     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.
    </P
><P
>&#13;     More information can be found at <A
HREF="http://www.ciphersbyritter.com/GLOSSARY.HTM#IV"
TARGET="_top"
>http://www.ciphersbyritter.com/GLOSSARY.HTM#IV</A
>, <A
HREF="http://fn2.freenet.edmonton.ab.ca/~jsavard/crypto/co0409.htm"
TARGET="_top"
>http://fn2.freenet.edmonton.ab.ca/~jsavard/crypto/co0409.htm</A
> and in chapter 9.3 of
     Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a discussion of
     this topic.
    </P
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