(PHP 3>= 3.0.8, PHP 4 , PHP 5)
mcrypt_create_iv --
Create an initialization vector (IV) from a random source
Description
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. MCRYPT_RAND is the only one supported on Windows
because Windows (of course) doesn't have /dev/random or /dev/urandom.
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);
?>
|
|
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
loosing security.
More information can be found at http://www.ciphersbyritter.com/GLOSSARY.HTM#IV, http://fn2.freenet.edmonton.ab.ca/~jsavard/crypto/co0409.htm and in chapter 9.3 of
Applied Cryptography by Schneier (ISBN 0-471-11709-9) for a discussion of
this topic.
