Technical Report CS753

TR#:CS753
Class:CS
Title: NEW TYPES OF CRYPTANALYTIC ATTACKS USING RELATED KEYS
Authors: Eli Biham
PDFCS0753.pdf
Abstract: In this paper we study the influence of key scheduling algorithms on the strength of blockciphers. We show that obvious relationships between keys exist in key scheduling algorithms of many blockciphers, and use these key relations to attack the blockciphers. types of attacks are described: New low-complexity chosen key attacks and new chosen plain text reductions of the complexity of exhaustive search attacks (and the faster variants based on complementation properties). These attacks are independent of the number of rounds of the cryptosystems and of the details of the F-function and may have very small complexities. These attacks show that the key scheduling algorithm should be carefully designed and that its structure should not be too simple. These attacks are applicable to both variants of LOKI. to Lucifer and could be applicable to DES if all the shifts in the key scheduling algorithm were the same.
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