Most formal approaches to security protocol analysis are based on a set of assumptions commonly referred to as the "Dolev-Yao model." In this paper, we use a multiset rewriting formalism, based on linear logic, to state the basic assumptions of this model. A characteristic of our formalism is the way that existential quantification provides a succinct way of choosing new values, such as new keys or nonces. We define a class of theories in this formalism that correspond to finite-length protocols, with a bounded initial-ization phase but allowing unboundedly many instances of each protocol role (e.g., client, server, initiator, or respon-der). Undecidability is proved for a restricted class of these protocols, and PSPACE-completeness is claimed for a class further restricted to have no new data (nonces). Since it is a fragment of linear logic, we can use our notation directly as input to linear logic tools, allowing us to do proof search for attacks with relatively little programming effort, and to formally verify protocol transformations and optimizations.

The Concurrent Logical Framework, or CLF, is a new logical framework in which concurrent computations can be represented as monadic objects, for which there is an intrinsic notion of concurrency. It is designed as a conservative extension of the linear logical framework LLF with the synchronous connectives ⊗, 1, !, and ∃ of intuitionistic linear logic, encapsulated in a monad. LLF is itself a conservative extension of LF with the asynchronous connectives −•, & and. The present report, the first of two technical reports describing CLF, presents the framework itself and its meta-theory. A novel, algorithmic formulation of the underlying type theory concentrating on canonical forms leads to a simple notion of definitional equality for concurrent computations in which the order of independent steps cannot be distinguished. The new formulation of the framework constitutes an original contribution even for the LF fragment. For many additional examples illustrating the use of the framework to specify and reason about object systems of interest, the reader is referred to the companion technical report on applications [CPWW02].

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