Fault-Tolerant Non-interference Extended Version

Abstract. This paper is about ensuring security in unreliable systems. We study systems which are subject to transient faults – soft errors that cause stored values to be corrupted. The classic problem of fault tolerance is to modify a system so that it works despite a limited number of faults. We introduce a novel variant of this problem. Instead of demanding that the system works despite faults, we simply require that it remains secure: wrong answers may be given but secrets will not be revealed. We develop a software-based technique to achieve this fault-tolerant non-interference property. The method is defined on a simple assembly language, and guarantees security for any assembly program provided as input. The security property is defined on top of a formal model that encompasses both the fault-prone machine and the faulty environment. A precise characterization of the class of programs for which the method guarantees transparency is provided.