Tamper-Tolerant Diagnosability Under Bounded or Unbounded Attacks

Abstract

This paper discusses fault diagnosis and diagnosability analysis in discrete-event systems modeled with nondeterministic finite automata, partially observed via a sensor measuring unit whose measurements (reported observations) may be vitiated by a malicious attacker. The attacks considered in this paper include arbitrary deletions, insertions, or substitutions of observed symbols. Assuming that each deletion, insertion, or substitution bears a positive cost to the attacker, two scenarios are taken into account: (1) a bounded number of attacks or, more generally, a total cost constraint on tampering actions; (2) an infinite number of attacks or, more generally, no constraints on the total cost of tampering actions. Several examples are presented to demonstrate the influence of cost constraints on tamper-tolerant diagnosis and tamper-tolerant system diagnosability.