Creates an initialization vector (IV) from a random source (original) (raw)

mcrypt_create_iv

(PHP 4, PHP 5, PHP 7 < 7.2.0, PECL mcrypt >= 1.0.0)

mcrypt_create_iv — Creates an initialization vector (IV) from a random source

Warning

This function was DEPRECATED in PHP 7.1.0, and_REMOVED_ in PHP 7.2.0.

Alternatives to this function include:

random_bytes()

Description

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

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 ofsource.
5.3.0	MCRYPT_DEV_RANDOM andMCRYPT_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); <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>i</mi><mi>v</mi><mo>=</mo><mi>m</mi><mi>c</mi><mi>r</mi><mi>y</mi><mi>p</mi><msub><mi>t</mi><mi>c</mi></msub><mi>r</mi><mi>e</mi><mi>a</mi><mi>t</mi><msub><mi>e</mi><mi>i</mi></msub><mi>v</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">iv = mcrypt_create_iv(</annotation></semantics></math>iv=mcryptcreateiv(size, MCRYPT_DEV_RANDOM); ?>