Events in security protocols

Abstract

The events of a security protocol and their causal dependency can play an important role in the analysis of security properties. This insight underlies both strand spaces and the inductive method. But neither of these approaches builds up the events of a protocol in a compositional way, so that there is an informal spring from the protocol to its model. By broadening the models to certain kinds of Petri nets, a restricted form of contextual nets, a compositional eventbased semantics is given to an economical, but expressive, language for describing security protocols; so the events and dependency of a wide range of protocols are determined once and for all. The net semantics is formally related to a transition semantics, strand spaces and inductive rules, as well as trace languages and event structures, so unifying a range of approaches, as well as providing conditions under which particular, more limited, models are adequate for the analysis of protocols. The net semantics allows the derivation of general properties and proof principles which are demonstrated in establishing an authentication property, following a diagrammatic style of proof.

Events, Causality and Symmetry

“…Name generation: There are methods to represent the generation of new names in causal models, e.g. [23,92,108]. But the methods are overly concrete in the sense that they ignore the implicit symmetry on names.…”

“…[59], and become increasingly so as chip design is forced to count the cost of communication [70]. Significant advances have been made in the more limited regime of security protocols [23,43,92]there are gaps in the treatment and exploitation of symmetry, and in relations with cryptography, which calls for probability. Two other specialized areas which rely on causal models, and probabilistic event structures [97], are the distributed diagnosis of communication networks [10], and the very recent Bayesian analysis of event-based trust [71].…”

“…• Security protocols: for example, strand spaces are a form of event structure which support reasoning about secrecy and authentication through causal relations [19,23,92]; • Systems biology: biologists rediscovered Petri nets in the analysis of chemical pathways (with conditions standing for molecular species and events for reactions).…”

A Formal Semantics for Protocol Narrations

“…On the other hand, strand spaces have also been studied by Crazzolara and Winskel in comparison to other models of concurrency [CW01,CW02], notably including event structures Petri nets and the algebraic process language SPL; the latter is a simplified (since channel-free) spi-calculus that is enhanced with some form of pattern-matching (cf. also [HJ06] for pattern-matching in a more standard spi-calculus, and our comments below).…”

“…This, however, is not the case. In [CW01], for any given SPL-process P in some particularly restricted form called !-par process, Crazzolara and Winskel show how to formally and closely relate the net behavior Net(P ) to the strand space behavior Tr(P ). In contrast, they do not offer any way to translate strand spaces back into SPL-terms, which would be required to inherit the desired operational semantics.…”