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


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

$cipher = MCRYPT_TripleDES;
$block_size = mcrypt_get_block_size($cipher);
$iv = mcrypt_create_iv($block_size, MCRYPT_DEV_RANDOM);