Establishing and preserving protocol security goals.

We take a model-theoretic viewpoint on security goals and how to establish them. The models are (possibly fragmentary) executions. Security goals such as authentication and confidentiality are geometric sequents, i.e. implications Φ→Ψ where Φ and Ψ are built from atomic formulas without negations, implications, or universal quantifiers.Security goals are then statements about homomorphisms, where the source is a minimal (fragmentary) model of the antecedent Φ. If every homomorphism to a non-fragmentary, complete execution factors through a model in which Ψ is satisfied, then the goal is achieved. One can validate security goals via a process of information enrichment. We call this approach enrich-by-need protocol analysis.This idea also clarifies protocol transformation. A protocol transformation preserves security goals when it preserves the form of the information enrichment process. We formalize this idea using simulation relations between labeled transition systems. These labeled transition systems formalize the analysis of the protocols, i.e. the information enrichment process, not the execution behavior of the protocols. [ABSTRACT FROM AUTHOR]