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.