None of the Digest:: modules will serve your purpose, as those are geared towards producing a Digest. What you're looking at is called Symmetric Crypt. You can probably use Crypt::DES_EDE3 or Crypt::Blowfish (those are the ones that I would consider).

Make sure you read the documentation for the modules thoroughly. I only have sueprficial training in cryptography...

Best regards

-lem, but some call me fokat