KN-Cipher
# 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.

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 $GF(2^{33}).$

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."

## 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.

