(PHP 4 >= 4.0.2, PHP 5)
mcrypt_decrypt — Decrypts crypttext with given parameters
$cipher
   , string $key
   , string $data
   , string $mode
   [, string $iv
  ] )
   Decrypts the data and returns the unencrypted data.
  
cipherOne of the MCRYPT_ciphername constants, or the name of the algorithm as string.
key
       The key with which the data was encrypted. If the provided key size is
       not supported by the cipher, the function will emit a warning and return FALSE
      
data
       The data that will be decrypted with the given cipher
       and mode. If the size of the data is not n * blocksize,
       the data will be padded with '\0'.
      
modeOne of the MCRYPT_MODE_modename constants, or one of the following strings: "ecb", "cbc", "cfb", "ofb", "nofb" or "stream".
ivUsed for the initialization in CBC, CFB, OFB modes, and in some algorithms in STREAM mode. If the provided IV size is not supported by the chaining mode or no IV was provided, but the chaining mode requires one, the function will emit a warning and return FALSE.
   Returns the decrypted data as a string  or FALSE on failure.
  
| Version | Description | 
|---|---|
| 5.6.0 | Invalid keyandivsizes
        are no longer accepted. mcrypt_decrypt() will now throw
        a warning and returnFALSEif the inputs are invalid. Previously keys and
        IVs were padded with '\0' bytes to the next valid size. |