A new attack against Khazad

Abstract

Khazad is a new block cipher initially proposed as a candidate to the NESSIE project. Its design is very similar to Rijndael, although it is a 64-bit block cipher. In this paper, we propose a new attack that can be seen as an extension of the Square attack. It takes advantage of redundancies between the round key derivation and the round function, and also exploits some algebraic observations over a few rounds. As a result, we can break 5 rounds of Khazad faster than exhaustive key search. This is the best known cryptanalytic result against Khazad. © International Association for Cryptologic Research 2003.