A Differential Fault Attack on Grain-128a using MACs

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The 32-bit MAC of Grain-128a is a linear combination of the first 64 and then the alternative keystream bits. In this paper, the authors describe a successful differential fault attack on Grain-128a, in which they recover the secret key by observing the correct and faulty MACs of certain chosen messages. The attack works due to certain properties of the Boolean functions and corresponding choices of the taps from the LFSR. They present methods to identify the fault locations and then construct set of linear equations to obtain the contents of the LFSR and the NFSR.