PHP Manual: mcrypt

Description

string mcrypt_encrypt ( string cipher, string key, string data, string mode [, string iv] )

mcrypt_encrypt() encrypts the data and returns the encrypted data.

Cipher is one of the MCRYPT_ciphername constants of the name of the algorithm as string.

Key is the key with which the data will be encrypted. If it's smaller that the required keysize, it is padded with '\0'. It is better not to use ASCII strings for keys. It is recommended to use the mhash functions to create a key from a string.

Data is the data that will be encrypted with the given cipher and mode. If the size of the data is not n * blocksize, the data will be padded with '\0'. The returned crypttext can be larger that the size of the data that is given by data.

Mode is one of the MCRYPT_MODE_modename constants of one of "ecb", "cbc", "cfb", "ofb", "nofb" or "stream".

The IV parameter is used for the initialisation in CBC, CFB, OFB modes, and in some algorithms in STREAM mode. If you do not supply an IV, while it is needed for an algorithm, the function issues a warning and uses an IV with all bytes set to '\0'.

Example 1. mcrypt_encrypt() Example

<?php
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $key = "This is a very secret key";
    $text = "Meet me at 11 o'clock behind the monument.";
    echo strlen($text) . "\n";

    $crypttext = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_ECB, $iv);
    echo strlen($crypttext) . "\n";
?>

The above example will output:

42
64

See also mcrypt_module_open() for a more advanced API and an example.