Paper 2009/218 Original: eprint.iacr.org/2009/218 ↗

Efficient FPGA Implementations of High-Dimensional Cube Testers on the Stream Cipher Grain-128

Abstract

Cube testers are a generic class of methods for building disstinguishers, based on cube attacks and on algebraic property-testers. In this paper, we report on an efficient FPGA implementation of cube testers on the stream cipher Grain-128. Our best result (a distinguisher on Grain-128 reduced to 237 rounds, out of 256) was achieved after a computation involving 2^54 clockings of Grain-128, with a 256×32 parallelization. An extrapolation of our results with standard methods suggests the possibility of a distinguishing attack on the full Grain-128 in time 2^83, which is well below the 2^128 complexity of exhaustive search. We also describe the method used for finding good cubes (a simple evolutionary algorithm), and report preliminary results on Grain-v1 obtained with a bitsliced C implementation.