LOKI (cipher)

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LOKI is the name of a series of block ciphers from an Australian group led by Jennifer Seberry.

The original LOKI, later renamed LOKI89, was a Feistel cipher with 64-bit blocks taking a 64-bit key. It had some weaknesses. LOKI was designed before differential cryptanalysis first appeared in the open literature, and published at about the same time as the first differential cryptanalysis paper. It turned out to have some weaknesses against that. Also, Lars Knudsen found a weakness in the key schedule.

LOKI91 was a revised version, with those weaknesses fixed.

LOKI97 was designed as a candidate for the AES competition; it did not make it into the finals. Like all AES candidates, it uses 128-bit blocks and supports key sizes of 128, 192 or 256 bits. It is a 16-round Feistel cipher with an F function that is basically two rounds of an SP network. This contrasts with DES where the F function is a single SP round.

The cipher is freely available for any use. It has a home page; see external links.