Complexity and Unwinding for Intransitive Noninterference

The paper considers several definitions of information flow security for intransitive policies from the point of view of the complexity of verifying whether a finite-state system is secure. The results are as follows. Checking (i) P-security (Goguen and Meseguer), (ii) IP-security (Haigh and Young), and (iii) TA-security (van der Meyden) are all in PTIME, while checking TO-security (van der Meyden) is undecidable, as is checking ITO-security (van der Meyden). The most important ingredients in the proofs of the PTIME upper bounds are new characterizations of the respective security notions, which also lead to new unwinding proof techniques that are shown to be sound and complete for these notions of security, and enable the algorithms to return simple counter-examples demonstrating insecurity. Our results for IP-security improve a previous doubly exponential bound of Hadj-Alouane et al

Timing-Sensitive Information Flow Analysis for Synchronous Systems

Abstract. Timing side channels are a serious threat to the security of cryptographic algorithms. This paper presents a novel method for the timing-sensitive analysis of information flow in synchronous hardware circuits. The method is based on a parameterized notion of confidentiality for finite transition systems that allows one to model information leakage in a fine-grained way. We present an efficient decision procedure for system security and apply it to discover timing leaks in nontrivial hardware implementations of cryptographic algorithms.