A Leakage-Resilient Mode of Operation

A weak pseudorandom function (wPRF) is a pseudorandom functions with a relaxed security requirement, where one only requires the output to be pseudorandom when queried on random (and not adversarially chosen) inputs. We show that unlike standard PRFs, wPRFs are secure against memory attacks, that is they remain secure even if a bounded amount of information about the secret key is leaked to the adversary. As an application of this result we propose a simple mode of operation which – when instantiated with any wPRF – gives a leakage-resilient stream-cipher. Such a cipher is secure against any side-channel attack, as long as the amount of information leaked per round is bounded, but overall can be arbitrary large. This construction is simpler than the only previous one (Dziembowski-Pietrzak FOCS’08) as it only uses a single primitive (a wPRF) in a straight forward manner.