Mod n cryptanalysis, with applications against RC5P and M6

Abstract

We introduce “mod n cryptanalysis,” a form of partitioning attack that is effective against ciphers which rely on modular addition and bit rotations for their security. We demonstrate this attack with a mod 3 attack against RC5P, an RC5 variant that uses addition instead of XOR. We also show mod 5 and mod 257 attacks against some versions of a family of ciphers used in the FireWire standard. We expect mod n cryptanalysis to be applicable to many other ciphers, and that the general attack is extensible to other values of n.