We describe a method for reducing the complexity of temporal logic model checking in systems composed of many parallel processes. The goal is to check properties of the components of a system and then deduce global properties from these local properties. The main difficulty with this type of approach is that local properties are often not preserved at the global level. We present a general framework for using additional interface processes to model the environment for a component. These interface processes are typically much simpler than the full environment of the component. By composing a component with its interface processes and then checking properties of this composition, we can guarantee that these properties will be preserved at the global level. We give two example compositional systems based on the logic CTL*.

We introduce the spi calculus, an extension of the pi calculus designed for the description and analysis of cryptographic protocols. We show how to use the spi calculus, particularly for studying authentication protocols. The pi calculus (without extension) suffices for some abstract protocols; the spi calculus enables us to consider cryptographic issues in more detail. We represent protocols as processes in the spi calculus and state their security properties in terms of coarsegrained notions of protocol equivalence.

In this paper we analyse the well known Needham-Schroeder Public-Key Protocol using FDR, a refinement checker for CSP. We use FDR to discover an attack upon the protocol, which allows an intruder to impersonate another agent. We adapt the protocol, and then use FDR to show that the new protocol is secure, at least for a small system. Finally we prove a result which tells us that if this small system is secure, then so is a system of arbitrary size. 1 Introduction In a distributed computer system, it is necessary to have some mechanism whereby a pair of agents can be assured of each other's identity---they should become sure that they really are talking to each other, rather than to an intruder impersonating the other agent. This is the role of an authentication protocol. In this paper we use the Failures Divergences Refinement Checker (FDR) [11, 5], a model checker for CSP, to analyse the Needham-Schroeder PublicKey Authentication Protocol [8]. FDR takes as input two CSP processes, ...

The notion of non-malleable cryptography, an extension of semantically secure cryptography, is defined. Informally, in the context of encryption the additional requirement is that given the ciphertext it is impossible to generate a different ciphertext so that the respective plaintexts are related. The same concept makes sense in the contexts of string commitment and zero-knowledge proofs of possession of knowledge. Non-malleable schemes for each of these three problems are presented. The schemes do not assume a trusted center; a user need not know anything about the number or identity of other system users. Our cryptosystem is the first proven to be secure against a strong type of chosen ciphertext attack proposed by Rackoff and Simon, in which the attacker knows the ciphertext she wishes to break and can query the decryption oracle on any ciphertext other than the target.

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Entity authentication and key distribution are central cryptographic problems in distributed computing -- but up until now, they have lacked even a meaningful definition. One consequence is that incorrect and inefficient protocols have proliferated. This paper provides the first treatment of these problems in the complexity-theoretic framework of modern cryptography. Addressed in detail are two problems of the symmetric, two-party setting: mutual authentication and authenticated key exchange. For each we present a definition, protocol, and proof that the protocol meets its goal, assuming the (minimal) assumption of pseudorandom function. When this assumption is appropriately instantiated, the protocols given are practical and efficient.

Active networks allow their users to inject customized programs into the nodes of the network. An extreme case, in which we are most interested, replaces packets with "capsules" -- program fragments that are executed at each network router/switch they traverse. Active architectures permit a massive increase in the sophistication of the computation that is performed within the network. They will enable new applications, especially those based on application-specific multicast, information fusion, and other services that leverage network-based computation and storage. Furthermore, they will accelerate the pace of innovation by decoupling network services from the underlying hardware and allowing new services to be loaded into the infrastructure on demand. In this paper, we describe our vision of an active network architecture, outline our approach to its design, and survey the technologies that can be brought to bear on its implementation. We propose that the research community mount a j...

For such self-organizing infrastructures as mobile ad hoc networks , envisioned to operate in an open, collaborative, and highly volatile environment, the importance of secu- rity cannot be underrated. The provision of comprehen- sive secure communication mandates that both route dis- covery and data forwarding be safeguarded. The discussed here Secure Routing Protocol (SRP) [1] counters malicious behavior that targets the discovery of topological informa- tion. The protection of the data transmission is a separate problem: an intermittently misbehaving attacker could first comply with the route discovery to make itself part of a route, and then corrupt the in-transit data. Protection of data transmission is addressed through our related Secure Message Transmission Protocol (SMT), which provides a flexible, end-to-end secure data forwarding scheme that naturally complement SRP. Here we discuss the design of SRP only, while SMT is the subject of another publication.

We present principles for the design of cryptographic protocols. The principles are neither necessary nor sufficient for correctness. They are however helpful, in that adherence to them would have avoided a considerable number of published errors. Our principles are informal guidelines. They complement formal methods, but do not assume them. In order to demonstrate the actual applicability of these guidelines, we discuss some instructive examples from the literature. 1

Two distinct, rigorous views of cryptography have developed over the years, in two mostly separate communities. One of the views relies on a simple but effective formal approach; the other, on a detailed computational model that considers issues of complexity and probability.