RSA Secret-Key Challenge
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The RSA Secret-Key Challenge is a series of cryptographic contests that were started by RSA Laboratories on January 28, 1997 with the intent of helping to demonstrate the relative security of different encryption algorithms. For each contest, RSA has posted on its website a block of ciphertext and the random initialization vector used for encryption. To win, a contestant must break the code by finding the original plaintext and the cryptographic key that will generate the posted ciphertext from the plaintext. The challenge consists of one DES contest and twelve contests based around the block cipher RC5.
The contests are associated with the distributed.net group, which has actively participated in the challenge by making use of distributed computing to perform a brute force attack.
Each of the RC5-* contests is named after the variant of the RC5 cipher used. The name RC5-w/r/b indicates that the cipher used w-bit words, r rounds, and a key made up of b bytes. The contests are often referred to by the names of the corresponding distributed.net projects, for example RC5-32/12/9 is often known as RC5-72 due to the 72-bit key size.
The first contest was DES Challenge III (and was also part of the DES Challenges), and was completed in just 22 hours 15 minutes by distributed.net and the EFF's Deep Crack machine.
RC5-32/12/7 was completed on 19 October 1997, with distributed.net finding the winning key in 250 days and winning the US$10,000 prize. The recovered plaintext was: The unknown message is: It's time to move to a longer key length.
RC5-32/12/8 also carried a US$10,000 prize and was completed by distributed.net on 14 July 2002. It took the group 1,757 days to locate the key, revealing the plaintext: The unknown message is: Some things are better left unread.
There are still eight remaining contests that have not yet been solved, RC5/32/12/9 through to RC5/32/12/16, each of which has a US$10,000 prize. Distributed.net is working on RC5-32/12/9 and is over 0.4% through as of march 2007.
