LOKI97

Infobox block cipher
name = LOKI97


caption = The LOKI97 round function
designers = Lawrie Brown, assisted by Jennifer Seberry and Josef Pieprzyk
publish date = 1998
derived from = LOKI91
derived to =
key size = 128, 192 or 256 bits
block size = 128 bits
structure = Feistel network
rounds = 16
cryptanalysis = Linear cryptanalysis against LOKI97, requiring 2⁵⁶ known plaintexts (Knudsen and Rijmen, 1999).

In cryptography, LOKI97 is a block cipher which was a candidate in the Advanced Encryption Standard competition. It is a member of the LOKI family of ciphers, earlier instances being LOKI89 and LOKI91. LOKI97 was designed by Lawrie Brown, assisted by Jennifer Seberry and Josef Pieprzyk.

Like DES, LOKI97 is a 16-round Feistel cipher, and like other AES candidates, has a 128-bit block size and a choice of a 128-, 192- or 256-bit key length. It uses 16 rounds of a balanced feistel network to process the input data blocks (see diagram right). The complex round function f incorporates two substitution-permutation layers in each round.The key schedule is also a Feistel structure — an unbalanced one unlike the main network — but using the same F-function.

The LOKI97 round function (shown right) uses two columns eachwith multiple copies of two basic S-boxes. These S-boxes aredesigned to be highly non-linear and have a good XOR profile. Thepermutations before and between server to provide auto-keying and todiffuse the S-box outputs as quickly as possible.

The authors have stated that, "LOKI97 is a non-proprietary algorithm, available for royalty-free use worldwide as a possible replacement for the DES or other existing block ciphers." It was intended to be an evolution of the earlier LOKI89 and LOKI91 block ciphers.

It was the first published candidate in the Advanced Encryption Standard competition, and was quickly analysed and attacked. An analysis of some problems with the LOKI97 design, which led to its rejection when shortlisting candidates, is given in the paper (Rijmen & Knudsen 1999). It was found to be susceptible to an effective theoretical differential cryptanalysis attack considerably faster than an exhaustive search.

ee also

* LOKI
* Advanced Encryption Standard competition

References

* L. Brown, J. Pieprzyk: Introducing the new LOKI97 Block Cipher
* L.R. Knudsen and V. Rijmen, "Weaknesses in LOKI97", Proceedings of the 2nd AES Candidate Conference, Rome, March 22-23, 1999, pp. 168–174.
* Wenling Wu, Bao Li, Denguo Feng, Sihan Qing, "Cryptanalysis of some AES candidate algorithms", Information and Communication Security - ICICS'99, LNCS 1726, pp 13-21, V Varadharajan (ed), Springer-Verlag 1999.
* Wenling Wu, Bao Li, Denguo Feng, Sihan Qing, "Linear cryptanalysis of LOKI97", Journal of Software, vol 11 no 2, pp 202-6, Feb 2000.

External links

* [http://www.unsw.adfa.edu.au/~lpb/research/loki97/ The LOKI97 homepage]
* [http://www.unsw.adfa.edu.au/~lpb/papers/ssp97/loki97b.html The design of LOKI97]
* [http://www.users.zetnet.co.uk/hopwood/crypto/scan/cs.html#LOKI97 SCAN's entry for LOKI97]
* [http://home.ecn.ab.ca/~jsavard/crypto/co040409.htm John Savard's Description of LOKI97]
* [http://serversniff.net/crypt_crypt.php Online-implementation of LOKI97 at serversniff.net]