Maximum likelihood-based key recovery algorithm from decayed key schedules

Abstract

A cold boot attack is a kind of side-channel attack that exploits a property of dynamic random-access memory. Using a cold boot attack, attackers can extract decayed key material from a running computer’s memory, which is a serious threat to computers using disk encryption software. Previously, an algorithm was presented that recovers a secret key from a decayed Advanced Encryption Standard key schedule. However, this method cannot recover a secret key if reverse bit flipping occurs, even in only one position, because this algorithm assumes a perfect asymmetric decay model. To remedy this limitation, we propose an algorithm based on the maximum likelihood approach, which can recover a secret key in an imperfect asymmetric decay model, i.e., where bit flipping occurs in both directions. We also give the theoretical bound of our algorithm and verify the validity thereof.