Abstract

. In this paper we analyse SAFER K-64 and show a weakness in the key schedule. It has the effect that for almost every key K, there exists at least one different key K , such that for many plaintexts the outputs after 6 rounds of encryption are equal. The output transformation causes the ciphertexts to differ in one of the 8 bytes. Also, the same types of keys encrypt even more pairs of plaintexts different in one byte to ciphertexts different only in the same byte. This enables us to do a related-key chosen plaintext attack on SAFER K-64, which finds 8 bits of the key requiring from 2 44 to about 2 47 chosen plaintexts. While our observations may have no greater impact on the security of SAFER K-64 when used for encryption in practice, it greatly reduces the security of the algorithm when used in hashing modes, which is illustrated. We give collisions for the well-known secure hash modes using a block cipher. Also we give a suggestion of how to improve the key schedule, such th...

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