   DES_DECRYPT(crypt_str[,key_str])

Decrypts a string encrypted with DES_ENCRYPT().
On error, this function returns NULL.

Note that this function works only if MySQL has been configured with
SSL support. See also : [Secure connections].

If no key_str argument is given, DES_DECRYPT() examines
the first byte of the encrypted string to determine the DES key number
that was used to encrypt the original string, and then reads the key
from the DES key file to decrypt the message.  For this to work,
the user must have the SUPER privilege. The key file can be specified
with the --des-key-file server option.

If you pass this function a key_str argument, that string
is used as the key for decrypting the message.

If the crypt_str argument doesn't look like an encrypted string,
MySQL will return the given crypt_str.
