Unformatted text preview: against Differential and Linear Cryptanalysis
The study of differential and linear cryptanalysis has shed significant light on the theory of good block cipher design. The inventors of IDEA introduced the concept of differentials, a generalization of the basic idea of characteristics [931]. They argued that block ciphers can be designed to resist this attack; IDEA is the result of that work [931]. This concept was further formalized in [1181,1182], when Kaisa Nyberg and Lars Knudsen showed how to make block ciphers provably secure against differential cryptanalysis. This theory has extensions to higherorder differentials [702,161,927,858,860] and partial differentials [860]. Higherorder differentials seem to apply only to ciphers with a small number of rounds, but partial differentials combine nicely with differentials. Linear cryptanalysis is newer, and is still being improved. Notions of key ranking [1019] and multiple approximations [811,812] have been defined. other work that extends the idea of linear cryptanalysis can be found in [1270]; [938] tries to combine linear and differential cryptanalysis into one attack. It is unclear what design techniques will protect against these sorts of attacks. Knudsen has made some progress, considering some necessary (but not perhaps sufficient) criteria for what he calls practically secure Feistel networks: ciphers that resist both linear and differential cryptanalysis [857]. Nyberg introduced in linear cryptanalysis an analogy to the concept of differentials from differential cryptanalysis [1180]. Interestingly enough, there seems to be a duality between differential and linear cryptanalysis. This duality becomes apparent both in the design of techniques to construct good differential characteristics and linear approximations [164,1018], and also in the design criteria for making algorithms that are secure against both attacks [307]. Exactly where this line of research will lead is still unknown. As a start, Daemen has developed an algorithmdesign strategy based on linear and differential cryptanalysis [402]....
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 Fall '10
 ALIULGER
 Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips

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