A Probabilistic Scheduler for the Analysis of Cryptographic Protocols 1

When modelling cryto-protocols by means of process calculi which express both nondeterministic and probabilistic behavior, it is customary to view the scheduler as an intruder. It has been established that the traditional scheduler needs to be carefully calibrated in order to more accurately reflect the intruder's capabilities for controlling communication channels. We propose such a class of schedulers through a semantic variant called PPCνσ, of the Probabilistic Poly-time Calculus (PPC) of Mitchell et al. [J.C. Mitchell, A. Ramanathan, A. Scedrov, and V. Teague. A probabilistic polynomial-time process calculus for the analysis of cryptographic protocols. Theoretical Computer Science, 353:118–164, 2006] and we illustrate the pertinence of our approach by an extensive study of the Dining Cryptographers (DCP) [David Chaum. The dining cryptographers problem: Unconditional sender and recipient untraceability. J. Cryptology, 1(1):65–75, 1988] protocol. Along these lines, we define a new characterization of Mitchell et al.'s observational equivalence [J.C. Mitchell, A. Ramanathan, A. Scedrov, and V. Teague. A probabilistic polynomial-time process calculus for the analysis of cryptographic protocols. Theoretical Computer Science, 353:118–164, 2006] more suited for taking into account any observable trace instead of just a single action as required in the analysis of the DCP.