International Association
for Cryptologic Research

Chaskey is a Message Authentication Code (MAC) for 32-bit microcontrollers proposed by Mouha et. al at SAC 2014. Its underlying blockcipher uses an Even-Mansour construction with a permutation

based on the ARX methodology. In this paper, we present key-recovery

attacks against Chaskey in the single and multi-user setting. These attacks are based on recent work by Fouque, Joux and Mavromati presented at Asiacrypt 2014 on Even-Mansour based constructions. We first

show a simple attack on the classical single-user setting which confirms

the security properties of Chaskey. Then, we describe an attack in the

multi-user setting and we recover all keys of 2^{43} users by doing 2^{43} queries

per user. Finally, we show a variant of this attack where we are able to

recover keys of two users in a smaller group of 2^{32} users.