Cryptanalysis of DES with a reduced number of rounds
Lecture notes in computer sciences; 218 on Advances in cryptology---CRYPTO 85
A proposal for a new block encryption standard
EUROCRYPT '90 Proceedings of the workshop on the theory and application of cryptographic techniques on Advances in cryptology
Markov ciphers and differential cryptanalysis
EUROCRYPT'91 Proceedings of the 10th annual international conference on Theory and application of cryptographic techniques
Miss in the Middle Attacks on IDEA and Khufu
FSE '99 Proceedings of the 6th International Workshop on Fast Software Encryption
A Unified Approach to Related-Key Attacks
Fast Software Encryption
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Large classes of weak keys have been found for the block cipher algorithm IDEA, previously known as IPES [2]. IDEA has a 128- bit key and encrypts blocks of 64 bits. For a class of 223 keys IDEA exhibits a linear factor. For a certain class of 235 keys the cipher has a global characteristic with probability 1. For another class of 251 keys only two encryptions and solving a set of 16 nonlinear boolean equations with 12 variables is sufficient to test if the used key belongs to this class. If it does, its particular value can be calculated efficiently. It is shown that the problem of weak keys can be eliminated by slightly modifying the key schedule of IDEA.