Paper 2009/282

Leakage-Resilient Signatures

Sebastian Faust, Eike Kiltz, Krzysztof Pietrzak, and Guy Rothblum

Abstract

The strongest standard security notion for digital signature schemes is unforgeability under chosen message attacks. In practice, however, this notion can be insufficient due to ``side-channel attacks'' which exploit leakage of information about the secret internal state of the scheme's hardware implementation. In this work we put forward the notion of ``leakage-resilient signatures,'' which strengthens the standard security notion by giving the adversary the additional power to learn a bounded amount of arbitrary information about the secret state that was accessed during every signature generation. This notion naturally implies security against all possible side-channel attacks as long as the amount of information leaked on each invocation is bounded and ``only computation leaks information.'' The main result of this paper is a construction which gives a (tree based, stateful) leakage-resilient signature scheme based on any 3-time signature scheme. The amount of information that our scheme can safely leak per signature generation is $1/3$ of the information the underlying 3-time signature scheme can leak in total. Based on recent works by Alwen, Dodis, Wichs and by Katz we give several efficient instantiations of 3-time signature schemes with the required security properties, hence yielding the first constructions of provably secure leakage-resilient signature schemes.