The LOKI91 Block Cipher

LOKI91 is a new private key block cipher designed in 1991, with 64-bit data and a 64-bit key. The data computation uses 16 rounds of a balanced feistel network with a complex function f using four 12->8 bit S-boxes and a 32-bit permutation. The overall structure design and analysis of LOKI91 was performed by Dr Lawrie Brown, Professors Josef Pieprzyk and Jennifer Seberry, and Matthew Kwan. The design and analysis of the S-box functions was done by Prof. Pieprzyk.

It was derived from the earlier LOKI89 64-bit block cipher designed in 1989 and described in my PhD thesis. LOKI91 includes minor changes to the key schedule and the function used to create the S-boxes to improve its immunity to analysis.

Some more details about LOKI89 and LOKI91 are provided, extracted from the lecture notes for my course in " Cryptography and Computer Security".

LOKI89 was described in: L. Brown, Josef Pieprzyk and Jennifer Seberry, " LOKI - A Cryptographic Primitive for Authentication and Secrecy Applications", Technical Report CS1/90, 18 Jan 1990. Also published in Advances in Cryptology - Auscrypt'90, Lecture Notes in Computer Science, vol 453, pp229-236, J Seberry, J Pieprzyk (eds), Springer-Verlag, 1990.

LOKI91 was described in: L. Brown, M Kwan, J Pieprzyk, J Seberry, " Improving Resistance to Differential Cryptanalysis and the Redesign of LOKI", Technical Report CS19/91, July 1991. Also published in Advances in Cryptology - Asiacrypt'91", Lecture Notes in Computer Science, vol 739, pp 36-50, H Imai et al (eds), Springer-Verlag, 1993.

A list of some of the published papers on LOKI89 and LOKI91 is available.

LOKI91 is a non-proprietary algorithm, available for royalty-free use worldwide as a possible replacement for the DES or other existing block ciphers.

Sample LOKI89/91 source in C (as a Unix shar file) is available, as supplied to Bruce Schneier for use in his classic text: B Schneier, "Applied Cryptography", 2/e, Wiley, 1996.

Dr Lawrie Brown / 30 Apr 99