In 1997 RSA Labs, the research arm of RSA Datasecurity Inc., issued a series of challanges to the internet cryptography community. RSA Labs offered a series of prizes for the first entity to correctly report the full plain text of a message encrypted with DES with a 56 bit key, and the full plain text of several messages encrypted with RC5 with various key lengths. The Labs posted all information necessary for anyone to perform a partial known plain text attacks against the encryptions.
The RSAChal software package was written to try and solve the RSA Labs RC5 challenges.
RSAChal can be downloaded from the development web page.