ran- dom over the entire 256 1 keyspace, would require about 1000 years of CPU time. The rapid progress in computer speed proved this belief utterly wrong. In 1997, the company RSA Security issued a public challenge to crack DES. The challenge was successfully met that same year after only 96 days of computation, using a network of no less than 14000 computers. In the two following years, other teams succeeded in cracking DES in 41 days, then in 56 hours, then in 22 hours and 15 minutes! The machine used for the 56-hour record, nicknamed Deep Crack, used 27 parallel motherboards, each one with 64 processor chips (1728 total) capable altogether of performing 90 billion key tests per second. The simple way to improve DES strength and security was to achieve double and triple encryption with two and three independent secret keys, respectively. These double- DES (2DES) and triple-DES (3DES) approaches, which bring the effective key size to 2 X = 112 bits and 3 56 = 168 bits, respectively, were endorsed in 1999 by NIST (National Institute of Standards and Technologies), the new name of the original standardization body that launched DES. 12 In 2DES, the DES algorithm is implemented just twice in a row with two independent secret keys, which brings the effective key length to 56 + 56 = 112. Note that doubling the key length squares the complexity (the size of the keyspace), namely, (256)2 = 2112 = Thus, Deep Crack, which is able to check out 109 keys per second would now require 5 X 1024 seconds of CPU time, corresponding to 1 X 1017 years or about 15 centuries! Even after an improbable increase of CPU power by one billionfold, this brute-force attack would require 1 X 108 years or four centuries! But Diffie and Hellman once proved that the effective number of keys is not given by the above figures; the 2DES keyspace is merely doubled, namely 257. which does not increase safety SO much with respect to standard DES. 12 Note that DES was also approved by ANSI (American Standards Institute) under the name of data encrypti