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Treyfer

In cryptography, Treyfer is a block cipher/ MAC designed in 1997 by Gideon Yuval. Aimed at smart card applications, the algorithm is extremely simple and compact; it can be implemented in just 29 bytes of 8051 machine code.

Treyfer has a rather small key size and block size of 64 bits each. All operations are byte-oriented, and there is a single 8×8-bit S-box. The S-box is left undefined; the implementation can simply use whatever data is available in memory. In each round, each byte has added to it the S-box value of the sum of a key byte and the previous data byte, then it is rotated left one bit. The design attempts to compensate for the simplicity of this round transformation by using a large number of rounds: 32.

Due to the simplicity of its key schedule, using the same 8 key bytes in each round, Treyfer was one of the first ciphers shown to be susceptible to a slide attack. This cryptanalysis, which is independent of the number of rounds and the choice of S-box, requires 2 known plaintexts and 2 computation time.