Funcion crypt

Esto lo encontre en la ayuda de PHP, no tuve tiempo para traducirlo:
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Encrypts plaintext with given parameters (PHP 4 >= 4.0.2, PHP 5)
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 920. mcrypt_encrypt() Example
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<?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";
?>
Estos son los tipos de encriptacion:
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Mcrypt ciphers
Here is a list of ciphers which are currently supported by the mcrypt extension. For a complete list of supported ciphers, see the defines at the end of mcrypt.h. The general rule with the mcrypt-2.2.x API is that you can access the cipher from PHP with MCRYPT_ciphername. With the libmcrypt-2.4.x and libmcrypt-2.5.x API these constants also work, but it is possible to specify the name of the cipher as a string with a call to mcrypt_module_open() <function.mcrypt-module-open.html>.
MCRYPT_3DES
MCRYPT_ARCFOUR_IV (libmcrypt > 2.4.x only)
MCRYPT_ARCFOUR (libmcrypt > 2.4.x only)
MCRYPT_BLOWFISH
MCRYPT_CAST_128
MCRYPT_CAST_256
MCRYPT_CRYPT
MCRYPT_DES
MCRYPT_DES_COMPAT (libmcrypt 2.2.x only)
MCRYPT_ENIGMA (libmcrypt > 2.4.x only, alias for MCRYPT_CRYPT)
MCRYPT_GOST
MCRYPT_IDEA (non-free)
MCRYPT_LOKI97 (libmcrypt > 2.4.x only)
MCRYPT_MARS (libmcrypt > 2.4.x only, non-free)
MCRYPT_PANAMA (libmcrypt > 2.4.x only)
MCRYPT_RIJNDAEL_128 (libmcrypt > 2.4.x only)
MCRYPT_RIJNDAEL_192 (libmcrypt > 2.4.x only)
MCRYPT_RIJNDAEL_256 (libmcrypt > 2.4.x only)
MCRYPT_RC2
MCRYPT_RC4 (libmcrypt 2.2.x only)
MCRYPT_RC6 (libmcrypt > 2.4.x only)
MCRYPT_RC6_128 (libmcrypt 2.2.x only)
MCRYPT_RC6_192 (libmcrypt 2.2.x only)
MCRYPT_RC6_256 (libmcrypt 2.2.x only)
MCRYPT_SAFER64
MCRYPT_SAFER128
MCRYPT_SAFERPLUS (libmcrypt > 2.4.x only)
MCRYPT_SERPENT(libmcrypt > 2.4.x only)
MCRYPT_SERPENT_128 (libmcrypt 2.2.x only)
MCRYPT_SERPENT_192 (libmcrypt 2.2.x only)
MCRYPT_SERPENT_256 (libmcrypt 2.2.x only)
MCRYPT_SKIPJACK (libmcrypt > 2.4.x only)
MCRYPT_TEAN (libmcrypt 2.2.x only)
MCRYPT_THREEWAY
MCRYPT_TRIPLEDES (libmcrypt > 2.4.x only)
MCRYPT_TWOFISH (for older mcrypt 2.x versions, or mcrypt > 2.4.x )
MCRYPT_TWOFISH128 (TWOFISHxxx are available in newer 2.x versions, but not in the 2.4.x versions)
MCRYPT_TWOFISH192
MCRYPT_TWOFISH256
MCRYPT_WAKE (libmcrypt > 2.4.x only)
MCRYPT_XTEA (libmcrypt > 2.4.x only)
Espero que te ayude, pues no he programado mucho en PHP.