A pure labeled transition semantics for the applied pi calculus

The applied pi calculus proposed by Abadi and Fournet is successful in the analysis of security protocols. Its semantics mainly depends on several structural rules. Structural rules are convenient for specification, but inefficient for implementation. In this paper, we establish a new semantics for applied pi calculus based upon pure labeled transition system and propose a new formulation of labeled bisimulation. We prove that the new labeled bisimularity coincides with observational equivalence. A zero-knowledge protocol is given as an example to illustrate the effectiveness of this new semantics.