Differential cryptanalysis of nimbus

Abstract

Nimbus is a block cipher submitted as a candidate to the NESSIE project by Alexis Machado.Lik e many other ciphers Nimbus combines multiplication operations with XOR operations, a common technique to protect against various kinds of cryptanalysis.In this paper we present two new differential properties of multiplication operations with probability about 1/2 which we use to design a one-round iterative characteristic of Nimbus.W e iterate it to a characteristic of the full cipher with probability 1/32, which in turn we use to attack the full cipher and find all the key material using 256 chosen plaintexts and 210 complexity. Th us, we show that the inclusion of multiplication operations in a cipher does not necessarily protect against attacks.