An attack on 6-round XSL-block ciphers

We study XSL block cipher with a key schedule algorithm based on a second-order recurrence relation and an inverse matrix of linear transform such that there exists a row with at least two equal elements. In this paper, we propose an attack on reduced 6-round XSL block ciphers based on combining of meet-in-the-middle technique, impossible differential technique, and zero-difference pattern. Firstly, we use meet-in-the-middle technique to form a set of the first round key candidates. Secondly, we use impossible differential technique and zero-difference pattern to get a distinguisher to obtain a set of the sixth round key candidates. The probability of success is 0.7. We check our attack on 16-bit XSL block ciphers.