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.