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Using Animation to Improve Formal Specifications of Security Protocols

The verification of cryptographic protocols has greatly improved these last years. Automated tools such as AVISPA provide real help in finding and characterizing attacks. The counterpart is the formal specification of the protocol, using an appropriate language such as HLPSL. Since HLPSL is a very expressive language, this stage is complicated and error-prone before a correct specification is eventually obtained. The verification tools of AVISPA are not designed to detect such specification errors. Unfortunately, as long as it contains typo-like errors, the verification of a HLPSL specification is pointless. In this paper, we propose an animation tool called SPAN †. It turns a formal protocol specification into an execution diagram, according to user choices. We show how the visualization eases the formal specification stage in many ways: drawing of typical execution diagrams, visualization of protocol termination, understanding of interleaved sessions, detection of unwanted side effects, etc. We also show how visualization and simulation of an intruder helps in finding attacks that are not automatically detected by tools.