Crypt::DES_EDE3 implements DES-EDE3 encryption. This is triple-DES 
encryption where an encrypt operation is encrypt-decrypt-encrypt, and 
decrypt is decrypt-encrypt-decrypt. This implementation uses Crypt::DES 
to do its dirty DES work, and simply provides a wrapper around that
module: setting up the individual DES ciphers, initializing the keys, 
and performing the encryption/decryption steps.

DES-EDE3 encryption requires a key size of 24 bytes.
