The Rectangle Attack — Rectangling the Serpent

Serpent is one of the 5 AES finalists. The best attack published so far analyzes up to 9 rounds. In this paper we present attacks on 7-round, 8-round, and 10-round variants of Serpent. We attack a 7-round variant with all key lengths, and 8- and 10-round variants with 256-bit keys. The 10-round attack on the 256-bit keys variants is the best published attack on the cipher. The attack enhances the amplified boomerang attack and uses better differentials. We also present the best 3-round, 4-round, 5-round and 6-round differential characteristics of Serpent.