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# mcrypt_create_iv

mcrypt_create_iv -- Create an initialization vector (IV) from a random source

## Description

`string mcrypt_create_iv`(int size, int source);

mcrypt_create_iv() is used to create an IV.

mcrypt_create_iv() takes two arguments, `size` determines the size of the IV, `source` specifies the source of the IV.

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.

Example 1. mcrypt_create_iv example
      1
      2 <?php
      3 $cipher = MCRYPT_TripleDES;
      4 $block_size = mcrypt_get_block_size($cipher);
      5 $iv = mcrypt_create_iv($block_size, MCRYPT_DEV_RANDOM);
      6 ?>
      7

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