I came across this interesting article by Bruce Schneier, widely regarded as one of the world's top experts on cryptography. He described a system of cryptography that requires nothing more than a deck of cards, yet is strong enough that it can withstand attack by powerful computers. An agent might be in a situation where he just does not have access to a computer, or may be prosecuted if he has tools for secret communication. But a deck of cards...what harm is that?

Solitaire gets its security from the inherent randomness in a shuffled deck of cards. By manipulating this deck, a communicant can create a string of "random" letters that he then combines with his message. Of course Solitaire can be simulated on a computer, but it is designed to be implemented by hand.

Solitaire may be low-tech, but its security is intended to be high-tech. I designed Solitaire to be secure even against the most well-funded military adversaries with the biggest computers and the smartest cryptanalysts.http://www.schneier.com/solitaire.html

I'll never trust anyone with two jokers again...:D