
Mike Jewell says: "One of the Perplex City cards, 13th Labour, involves cracking an RC5-encrypted plaintext. There is now a client available at the above link, and we're looking for people to join our distributed solving effort. Prizes are available (both from Mind Candy and generous players). The client is written using .NET, and works on Mac/Linux via Mono as well as on XP."
Link (See previous Boing Boing coverage here.)