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Abstract. We present a new symbolic model checker which conservatively evaluates safety and liveness properties on infinite-state programs.We use Presburger formulas to symbolically encode a program's transition system, as well as its model-checking computations. All fixpoint calculations are executed symbolica~y, and their convergence is guaranteed by using approximation techniques. We demonstrate the promise of this technology on some well-known infinite-state concurrency problems.

Abstract. STRANGER is an automata-based string analysis tool for finding and eliminating string-related security vulnerabilities in PHP applications. STRANGER uses symbolic forward and backward reachability analyses to compute the possible values that the string expressions can take during program execution. STRANGER can automatically (1) prove that an application is free from specified attacks or (2) generate vulnerability signatures that characterize all malicious inputs that can be used to generate attacks.

This paper focuses on the realizability problem of a framework for modeling and specifying the global behavior of reactive electronic services (e-services). In this framework, Web accessible programs (peers) communicate by asynchronous message passing, and a virtual global watcher listens silently to the network. The global behavior is characterized by a conversation, which is the infinite sequence of messages observed by the watcher. We show that given a Büchi automaton specifying the desired set of conversations, called a conversation protocol, it is possible to implement it using a set of finite state peers if three realizability conditions are satisfied. In particular, the synthesized peers will conform to the protocol by generating only those conversations specified by the protocol. Our results enable a top-down verification strategy where: (1) A conversation protocol is specified by a realizable Büchi automaton, (2) The properties of the protocol are verified on the Büchi automaton specification, (3) The peer implementations are synthesized from the protocol via projection.

Since software systems are becoming increasingly more concurrent and distributed, modeling and analysis of interactions among their components is a crucial problem. In several application domains, message-based communication is used as the interaction mechanism, and the communication contract among the components of the system is specified semantically as a state machine. In the service-oriented computing domain such communication contracts are called "choreography" specifications. A choreography specification identifies allowable ordering of message exchanges in a distributed system. A fundamental question about a choreography specification is determining its realizability, i.e., given a choreography specification, is it possible to build a distributed system that communicates exactly as the choreography specifies? Checking realizability of choreography specifications has been an open problem for several years and it was not known if this was a decidable problem. In this paper we give necessary and sufficient conditions for realizability of choreographies. We implemented the proposed realizability check and our experiments show that it can efficiently determine the realizability of 1) web service choreographies, 2) Singularity OS channel contracts, and 3) UML collaboration (communication) diagrams.