(3.0.8 - 3.0.18 only, PHP 4 >= 4.0.0)
mcrypt_create_iv -- Create an initialization vector (IV) from a random sourcemcrypt_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.