Abstract. In this paper we present a differential fault attack that can be applied to the AES using a single fault. We demonstrate that when a single random byte fault is induced at the input of the eighth round, the AES key can be deduced using a two stage algorithm. The first step has a statistical expectation of reducing the possible key hypotheses to 2 32 , and the second step to a mere 2 8 . Furthermore, we show that, with certain faults, this can be reduced to two key hypothesis.

Observations of fluctuations in the redshifted 21-cm radiation from neutral hydrogen (H I) are perceived to be an important future probe of the universe at high redshifts. Under the assumption that at redshifts z 6 (post-reionization era) the H I traces the underlying dark matter with a possible bias, we investigate the possibility of using observations of redshifted 21-cm radiation to detect the bispectrum arising from non-linear gravitational clustering and from non-linear bias. We find that the expected signal is ∼ 0.1 mJy at 325 MHz (z = 3.4) for the small baselines at the Giant Metrewave Radio Telescope, the strength being a few times larger at higher frequencies (610 MHz, z = 1.3). Further, the magnitude of the signal from the bispectrum is predicted to be comparable to that from the power spectrum, allowing a detection of both in roughly the same integration time. The H I signal is found to be uncorrelated beyond frequency separations of ∼1.3 MHz whereas the continuum sources of contamination are expected to be correlated across much larger frequencies. This signature can in principle be used to distinguish the H I signal from the contamination. We also consider the possibility of using observations of the bispectrum to determine the linear and quadratic bias parameters of the H I at high redshifts, this having possible implications for theories of galaxy formation.

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