Syntax:
DES_ENCRYPT(str[,{key_num|key_str}])

Encrypts the string with the given key using the Triple-DES algorithm.

This function works only if MySQL has been configured with SSL support.
See http://dev.mysql.com/doc/refman/5.5/en/encrypted-connections.html.

The encryption key to use is chosen based on the second argument to
DES_ENCRYPT(), if one was given. With no argument, the first key from
the DES key file is used. With a key_num argument, the given key number
(0 to 9) from the DES key file is used. With a key_str argument, the
given key string is used to encrypt str.

The key file can be specified with the --des-key-file server option.

The return string is a binary string where the first character is
CHAR(128 | key_num). If an error occurs, DES_ENCRYPT() returns NULL.

The 128 is added to make it easier to recognize an encrypted key. If
you use a string key, key_num is 127.

The string length for the result is given by this formula:

new_len = orig_len + (8 - (orig_len % 8)) + 1

Each line in the DES key file has the following format:

key_num des_key_str

Each key_num value must be a number in the range from 0 to 9. Lines in
the file may be in any order. des_key_str is the string that is used to
encrypt the message. There should be at least one space between the
number and the key. The first key is the default key that is used if
you do not specify any key argument to DES_ENCRYPT().

You can tell MySQL to read new key values from the key file with the
FLUSH DES_KEY_FILE statement. This requires the RELOAD privilege.

One benefit of having a set of default keys is that it gives
applications a way to check for the existence of encrypted column
values, without giving the end user the right to decrypt those values.

URL: http://dev.mysql.com/doc/refman/5.5/en/encryption-functions.html

