As Keccak has been selected as the new SHA-3 standard, Message Authentication Code (MAC) (MAC-Keccak) using a secret key will be widely used for integrity checking and authenticity assurance. Recent works have shown the feasibility of side-channel attacks against software implementations of MAC-Keccak to retrieve the key, with the security assessment of hardware implementations remaining an open problem. In this paper, we present a comprehensive and practical side-channel analysis of a hardware implementation of MAC-Keccak on FPGA. Different from previous works, we propose a new attack method targeting the first round output of MAC-Keccak rather than the linear operation $\theta$ only. The results on sampled power traces show that the unprotected hardware implementation of MAC-Keccak is vulnerable to side-channel attacks, and attacking the nonlinear operation of MAC-Keccak is very effective. We further discuss countermeasures against side-channel analysis on hardware MAC-Keccak. Finally, we discuss the impact of the key length on side-channel analysis and compare the attack complexity between MAC-Keccak and other cryptographic algorithms.
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