SXAL/MBAL

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**SXAL**
Designer(s):	Laurel Intelligent Systems
First published:	1993-12
Key size(s):	64 bits
Block size(s):	64 bits
Structure:	Substitution-permutation network
Rounds:	8

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.

[edit] MBAL

MBAL is an encryption algorithm built using SXAL, but which can be applied to messages any number of bytes in length (at least 8). It uses two 64-bit extended keys for key whitening on the first 64 bits. The algorithm consists of 9 steps:

Pre-whitening
F_m: An expanded version of SXAL applied to the entire message
SXAL the block consisting of the first 4 and last 4 bytes
Reverse the byte order of the entire message
F_m
Reverse
SXAL the ends
F_m
Post-whitening

[edit] References

ISO/IEC9979-0012 Register Entry (PDF), registered 1995-10-23
U.S. Patent 6,038,321 , a patent on a communications system using SXAL/MBAL for encryption. Includes a description of SXAL/MBAL.