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Unformatted text preview: ure. A 512-bit key gives a complexity of 2512—inconceivable under any circumstances. Khafre
Khafre is the second of two cryptosystems proposed by Merkle . (Khufu and Khafre are names of Egyptian pharaohs.) It is similar in design to Khufu, except that it was designed for applications without precomputation time. The S-boxes are not key-dependent. Instead, Khafre uses fixed S-boxes. And the key is XORed with the encryption block not only before the first round and after the last round, but also after every 8 rounds of encryption. Merkle speculated that key sizes of 64- or 128-bits would be used for Khafre and that more rounds of encryption would be required for Khafre than for Khufu. This, combined with the fact that each round of Khafre is more complex than for Khufu, makes Khafre slower. In compensation, Khafre does not require any precomputation and will encrypt small amounts of data more quickly. In 1990 Biham and Shamir turned their differential cryptanalysis techniques against Khafre . They were able to break 16-round Khafre with a chosen-plaintext attack using about 1500 different encryptions. It took about an hour, using their personal computer. Converting that to a known-plaintext attack would require about 238 encryptions. Khafre with 24 rounds can be broken by a chosen-plaintext attack using 253 encryptions, and a known-plaintext attack using 259 encryptions. Patents
Both Khufu and Khafre are patented . Source code for the algorithms are in the patent. Anyone interested in licensing either or both algorithms should contact Director of Licensing, Xerox Corporation, P.O. Box 1600, Stamford, CT, 06904-1600. 13.8 RC2
RC2 is a variable-key-size encryption algorithm designed by Ron Rivest for RSA Data Security, Inc. (RSADSI). Apparently, “RC” stands for “Ron’s Code, ” although it officially stands for “Rivest Cipher.” (RC3 was broken at RSADSI during development; RC1 never got further than Rivest’s notebook.) It is proprietary, and its details have not been pu...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.
- Fall '10