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.