Abstract. Formal semantic definitions of concurrent languages, when specified in a well-suited semantic framework and supported by generic and efficient formal tools, can be the basis of powerful software analysis tools. Such tools can be obtained for free from the semantic definitions; in our experience in just the few weeks required to define a language’s semantics even for large languages like Java. By combining, yet distinguishing, both equations and rules, rewriting logic semantic definitions unify both the semantic equations of equational semantics (in their higher-order denotational version or their first-order algebraic counterpart) and the semantic rules of SOS. Several limitations of both SOS and equational semantics are thus overcome within this unified framework. By using a high-performance implementation of rewriting logic such as Maude, a language’s formal specification can be automatically transformed into an efficient interpreter. Furthermore, by using Maude’s breadth first search command, we also obtain for free a semi-decision procedure for finding failures of safety properties; and by using Maude’s LTL model checker, we obtain, also for free, a decision procedure for LTL properties of finite-state programs. These possibilities, and the competitive performance of the analysis tools thus obtained, are illustrated by means of a concurrent Caml-like language; similar experience with Java (source and JVM) programs is also summarized. 1

Rewriting logic is a flexible and expressive logical framework that unifies denotational semantics and SOS in a novel way, avoiding their respective limitations and allowing very succinct semantic definitions. The fact that a rewrite theory’s axioms include both equations and rewrite rules provides a very useful “abstraction knob” to find the right balance between abstraction and observability in semantic definitions. Such semantic definitions are directly executable as interpreters in a rewriting logic language such as Maude, whose generic formal tools can be used to endow those interpreters with powerful program analysis capabilities.

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The automatic analysis of cryptographic protocols by using formal methods on concurrent languages is a subject widely treated in the literature. From its beginning in the decade of the 70s, the field has been gaining maturity and consolidation. Some declarative approaches based on CLP, Haskell or Maude have been proposed for the specification and analysis of communication protocols. In this paper, we propose the Timed Concurrent Constraint Language (tccp in short) as the specification language for protocols. tccp is a declarative concurrent programming language which allows one to intuitively model concurrent and reactive systems. Cryptographic protocols can be specified in a very compact way thanks to certain features of the language such as the non-deterministic behavior and concurrency. We show how to specify the basic actions that are usually performed during a protocol run. Thereafter, we show how to specify the participants in the protocol. Finally, we specify the intruder model by means of a hostile environment in which principals run the protocol. The model considered for the intruder is the popular model of Dolev-Yao. We use along the paper the Needham-Schroeder public key authentication protocol to illustrate the approach. The basic actions and the intruder implementation can be reused for the specification of many different protocols.