Abstract: Complete Characterization of Security Protocols by Pattern Refinement (Work in Progress) Cas Cremers Recently, the notion of complete characterizations of security protocols was introduced by Guttman and Thayer. We provide an alternative definition of this concept, and extend an existing protocol verification tool (Scyther) to compute our notion of complete characterization.We present both notions of complete characterization, discuss their relative merits, and provide preliminary empirical results using an extended version of the Scyther tool.