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 (using the Short Scale), possible keys. One of the major criticism 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 to even a small nonprofit organization such as EFF.
Read more about this topic: EFF DES Cracker
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