RSA Laboratories

2.4.4 What is the RSA Secret Key Challenge?

RSA Laboratories started the RSA Secret Key Challenge in January 1997. The goal of the challenges is to quantify the security offered by secret-key ciphers (see Question 2.1.2) with keys of various sizes. The information obtained from these contests is anticipated to be of value to researchers and developers alike as they estimate the strength of an algorithm or application against exhaustive key-search.

Initially, thirteen challenges were issued, of which four have been solved as of January 2000. There were twelve RC5 challenges and one DES challenge, with key sizes ranging from 40 bits to 128 bits. The 56-bit DES challenge and the 40-, 48-, and 56-bit RC5 challenges have all been solved. The 56-bit RC5 key was found in October 1997 after 250 days of exhaustive key search on 10,000 idle computers. The project was part of the Bovine RC5 Effort headed by a group called and led by Adam L. Beberg, Jeff Lawson, and David McNett.

In January 1998, RSA Laboratories launched the DES challenge II, which consists of a series of DES challenges to be released twice per year. It has been expected that each time the amount of time needed to solve the challenge will decrease substantially. Indeed, in February 1998, solved RSA's DES Challenge II, using an estimated 50,000 processors to search 85% of the possible keys, in 41 days. In July 1998, the supercomputer DES Cracker designed by Electronic Frontier Foundation (EFF) was able to crack RSA's DES Challenge II-2 in 56 hours. The same computer, assisted by 100,000 PCs on the Internet, was able to crack DES Challenge III in only 22 hours; see

For more information about the challenges, send email to or visit the web site at

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