Implementations of the Advanced Encryption Standard (AES), including hardware applications with limited resources (e.g., smart cards), may be vulnerable to \side-channel attacks" such as dierential power analysis. One countermeasure against such attacks is adding a random mask to the data; this randomizes the statistics of the calculation at the cost of computing \mask corrections." The single nonlinear step in each AES round is the \S-box" (involving a Galois inversion), which incurs the majority of the cost for mask corrections. Oswald et al.(1) showed how the \tower eld" representation allows maintaining an additive mask throughout the Galois inverse calculation. This work applies a similar masking strategy to the most compact (unmasked) S-box to date(2). The result is the most compact masked S-box so far, with \perfect masking" (by the denition of Blomer(3)) giving suitable implementations immu- nity to rst-order dierential side-channel attacks.
['David Canright', 'Lejla Batina']
A Very Compact \Perfectly Masked" S-Box for AES (corrected)