SXAL/MBAL

SXAL/MBAL

Differential and linear cryptanalysis

In cryptography, SXAL (Substitution Xor ALgorithm, sometimes called SXAL8) is a block cipher designed in 1993 by Yokohama-based Laurel Intelligent Systems. It is normally used in a special mode of operation called MBAL (Multi Block ALgorithm). SXAL/MBAL has been used for encryption in a number of Japanese PC cards and smart cards.

SXAL is an 8-round substitution-permutation network with block size and key size of 64 bits each. All operations are byte-oriented. The algorithm uses a single 8×8-bit S-box K, designed so that both K(X) and X XOR K(X) are injective functions. In each round, the bytes of the block are first permuted. Then each byte is XORed with a key byte and an earlier ciphertext byte, processed through the S-box, and XORed with the previous plaintext byte.

The key schedule is rather complex, processing the key with SXAL itself, beginning with a null key and using permuted intermediate results as later keys.