PHP: password en- & decryption

gistfile1.aw

# http://stackoverflow.com/questions/1289061/best-way-to-use-php-to-encrypt-and-decrypt
$key = 'password to (en/de)crypt';
$string = ' string to be encrypted '; // note the spaces

# To Encrypt:
$encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $string, MCRYPT_MODE_CBC, md5(md5($key))));

# To Decrypt:
$decrypted = rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($encrypted), MCRYPT_MODE_CBC, md5(md5($key))), "\0");