2001-01-25

Steak - Key Setup

Steak may be used with any key size and any vector size n, although a vector size of 8 is recommended, since a smaller vector will disturb the probability distribution of the Feedback Process.

The Key Setup scheme begins with a calculation of a 837 + n * 8 byte sized hash value of the key. This hash value contains less than one byte too little information than what is theoretically necessary to calculate any quadruple of single cycle permutations of 256 elements to use as S-Boxes, plus any A vector and any initial value of the V vector. This negligible lack of information is sufficient to rule out the possibility of key collisions, as long as the provided key does not exceed the hash value in size. As a consequence, however, the lastly extracted byte would be biased towards zero unless an addition was made to the scheme. This addition consists of encrypting the residue from the S-Box extraction prior to the extraction of A and V with a default key.

Cf. the source code of TSteakCipher.SetUp in Steak.pas for details.