(PHP 4, PHP 5, PHP 7)
mcrypt_create_iv — Creates an initialization vector (IV) from a random source
$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.
sizeThe 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_RANDOMmay block until more entropy is available.
Returns the initialization vector, or FALSE on error.
| 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. |
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);
?>