In cryptography, the EFF DES cracker (nicknamed "Deep Crack") is a machine built by the Electronic Frontier Foundation (EFF) in 1998, to perform a brute force search of the Data Encryption Standard (DES) cipher's key space – that is, to decrypt an encrypted message by trying every possible key. The aim in doing this was to prove that the key size of DES was not sufficient to be secure. Detailed technical data of this machine, including block diagrams, circuit schematics, VHDL source code of the custom chips and its emulator, have all been published in the book Cracking DES. Its public domain license allows everyone to freely copy, use, or modify its design. To avoid the export regulation on cryptography by the US Government, the source code was distributed not in electronic form but as a hardcopy book, of which the open publication is protected by the First Amendment. Machine-readable metadata is provided to facilitate the transcription of the code into a computer via OCR by readers. Background DES uses a 56-bit key, meaning that there are 256 possible keys under which a message can be encrypted. This is exactly 72,057,594,037,927,936, or approximately 72 quadrillion possible keys. One of the major criticisms of DES, when proposed in 1975, was that the key size was too short. Martin Hellman and Whitfield Diffie of Stanford University estimated that a machine fast enough to test that many keys in a day would have cost about $20 million in 1976, an affordable sum to national intelligence agencies such as the US National Security Agency. Subsequent advances in the price/performance of chips kept reducing that cost until, twenty years later, it became affordable for even a small nonprofit organization such as the EFF to mount a realistic attack. The DES challenges DES was a federal standard, and the US government encouraged the use of DES for all non-classified data. RSA Security wished to demonstrate that DES's key length was not enough to ensure security, so they set up the DES Challenges in 1997, offering a monetary prize. The first DES Challenge was solved in 96 days by the DESCHALL Project led by Rocke Verser in Loveland, Colorado. RSA Security set up DES Challenge II-1, which was solved by distributed.net in 39 days in January and February 1998. In 1998, the EFF built Deep Crack (named in reference to IBM's Deep Blue chess computer) for less