... 3.0.8 - 3.0.18 only, PHP 4 >= 4.0.0) mcrypt_cfb -- Encrypt/decrypt data in CFB mode . string mcrypt_cfb ( int cipher, string key, string data, int mode, string iv)string mcrypt_cfb ( string cipher, string key, string data, int mode [, string iv]) . The first prototype is when linked against libmcrypt 2.2.x, the second when linked against libmcrypt 2.4.x. mcrypt_cfb() encrypts or decrypts (depending on mode ) the data with cipher and key in CFB cipher mode and returns the resulting string. ...