A Bottleneck Attack on Crypton
Abstract
Crypton is a 12-round blockcipher proposed as an AES candidate by C.H. Lim in 1998. In this paper, we present two bottleneck attacks on reduced round version of Crypton v0.5 and Crypton v1.0. Those cryptanalyses are built upon a four-round distinguisher based on a three-round property due to a restricted dependency of the one byte to one byte permutation transformation as made for the AES in [GM00].We present an attack on a six round version of Crypton. We also present a marginal speed up of the 128-bits key exhaustive search for a seven-round version of Crypton. This attack does not endanger the practical security offered by Crypton but shows an other example where the bottleneck property could be used with an S-box level composed of at least two S-boxes.