The block cipher MISTY1 [
9] proposed for the NESSIE project [
11] is a Feistel network augmented with key-dependent linear FL functions. The proposal allows a variable number of rounds provided
that it is a multiple of four.
Here we present a new attack - the Slicing Attack - on the 4-round version, which makes use of the special structure and position
of these key-dependent linear FL functions. While the FL functions were introduced to make attacks harder, they also present
a subtle weakness in the 4-round version of the cipher.
Keywords Block cipher - Cryptanalysis - Impossible Differential - Slicing Attack