KN-Cipher

In cryptography, KN-Cipher is a block cipher created by Kaisa Nyberg and Lars Knudsen in 1995. One of the first ciphers designed to be provably secure against ordinary differential cryptanalysis, KN-Cipher was later broken using higher order differential cryptanalysis.

KN-Cipher

General
Designers	Kaisa Nyberg and Lars Knudsen
First published	1995
Cipher detail
Key sizes	198 bits
Block sizes	64 bits
Structure	Feistel network
Rounds	6
Best public cryptanalysis
Jakobsen & Knudsen's higher order differential cryptanalysis breaks KN-Cipher with only 512 chosen plaintexts and 2^41 running time, or with 32 chosen plaintexts and 2^70 running time.[1]

Presented as "a prototype...compatible with DES", the algorithm has a 64-bit block size and a 6-round Feistel network structure. The round function is based on the cube operation in the finite field GF(2³³).

The designers did not specify any key schedule for the cipher; they state, "All round keys should be independent, therefore we need at least 198 key bits."[2]

Cryptanalysis

Jakobsen & Knudsen's higher order differential cryptanalysis breaks KN-Cipher with only 512 chosen plaintexts and 2⁴¹ running time, or with 32 chosen plaintexts and 2⁷⁰ running time.[1]

References

1. T. Jakobsen, L.R. Knudsen (January 1997). The Interpolation Attack on Block Ciphers (PDF/PostScript). 4th International Workshop on Fast Software Encryption (FSE '97). Haifa: Springer-Verlag. pp. 28–40. Retrieved 23 January 2007.
2. K. Nyberg, L.R. Knudsen (1995). "Provable Security Against a Differential Attack" (PDF/PostScript). Journal of Cryptology. 8 (1): 27–37. doi:10.1007/bf00204800. ISSN 0933-2790. Retrieved 23 January 2007.