Mcrypt Functions
PHP Manual

mcrypt_create_iv

Creates an initialization vector (IV) from a random source

Warning

This function was DEPRECATED in PHP 7.1.0.

Alternatives to this function include:

  • random_bytes

Description

string mcrypt_create_iv ( int $size [, int $source = MCRYPT_DEV_URANDOM ] )

Creates an initialization vector (IV) from a random source.

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.

Parameters

size

The size of the IV.

source

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). Prior to 5.3.0, MCRYPT_RAND was the only one supported on Windows.

Note that the default value of this parameter was MCRYPT_DEV_RANDOM prior to PHP 5.6.0.

Note: Note that MCRYPT_DEV_RANDOM may block until more entropy is available.

Return Values

Returns the initialization vector, or FALSE on error.

Changelog

Version Description
5.6.0 MCRYPT_DEV_URANDOM is now the default value of source.
5.3.0 MCRYPT_DEV_RANDOM and MCRYPT_DEV_URANDOM became available on Windows platforms.
5.3.0 It is no longer required to call srand first. This is now done automatically.

Examples

Example #1 mcrypt_create_iv Example

<?php
    $size = mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CFB);
    $iv = mcrypt_create_iv($size, MCRYPT_DEV_RANDOM);
?>

See Also