Abstract: The AVISS Security Protocol Analysis Tool Alessandro Armando and David Basin and Mehdi Bouallagui and Yannick Chevalier and Luca Compagna and Sebastian Mödersheim and Michael Rusinowitch and Mathieu Turuani and Luca Viganò and Laurent Vigneron We introduce AVISS, a tool for security protocol analysis that supports the integration of back-ends implementing different search techniques, allowing for their systematic and quantitative comparison and paving the way to their effective interaction. As a significant example, we have implemented three back-ends, and used the AVISS tool to analyze and find flaws in 36 protocols, including 31 problems in the Clark-Jacob's protocol library and a previously unreported flaw in the Denning-Sacco protocol.