mcrypt_cfb
mcrypt_decrypt
Mcrypt Funções
PHP Manual

# mcrypt_create_iv

(PHP 4, PHP 5)

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

### Descrição

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

Create 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.

### Parâmetros

`size`

  Determines the size of the IV, parameter `source` (defaults to random value) specifies the source of the IV.

`source`

  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). `MCRYPT_RAND` is the only one supported on Windows because Windows (of course) doesn't have /dev/random or /dev/urandom.

  > Nota: When using `MCRYPT_RAND`, remember to call srand() before mcrypt_create_iv() to initialize the random number generator; it is not seeded automatically like rand() is.

### Valor Retornado

Returns the initialization vector, or `FALSE` on error.

### Exemplos

Exemplo #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);
?>`

### Veja Também

- » http://www.ciphersbyritter.com/GLOSSARY.HTM#IV
- » http://www.quadibloc.com/crypto/co0409.htm
- Chapter 9.3 of Applied Cryptography by Schneier (ISBN 0-471-11709-9)

mcrypt_cfb
mcrypt_decrypt
Mcrypt Funções
PHP Manual