SXAL/MBAL

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SXAL
General
Designers	Laurel Intelligent Systems
First published	December 1993
Cipher detail
Key sizes	64 bits
Block sizes	64 bits
Structure	Substitution-permutation network
Rounds	8
Best public cryptanalysis
Differential and linear cryptanalysis[1]

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 that 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:

1. Pre-whitening
2. F_m: An expanded version of SXAL applied to the entire message
3. SXAL the block consisting of the first 4 and last 4 bytes
4. Reverse the byte order of the entire message
5. F_m
6. Reverse
7. SXAL the ends
8. F_m
9. Post-whitening

MBAL has been shown to be susceptible to both differential cryptanalysis and linear cryptanalysis.^[1]

[edit] References

1. ^ ^{a b} Schneier, Bruce (1996). Applied Cryptography, Second Edition. John Wiley & Sons, p.344. ISBN 0-471-11709-9. 

[edit] External links

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

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