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, ...

We present a new tool, named DART, for automatically testing software that combines three main techniques: (1) automated extraction of the interface of a program with its external environment using static source-code parsing; (2) automatic generation of a test driver for this interface that performs random testing to simulate the most general environment the program can operate in; and (3) dynamic analysis of how the program behaves under random testing and automatic generation of new test inputs to direct systematically the execution along alternative program paths. Together, these three techniques constitute Directed Automated Random Testing,or DART for short. The main strength of DART is thus that testing can be performed completely automatically on any program that compiles – there is no need to write any test driver or harness code. During testing, DART detects standard errors such as program crashes, assertion violations, and non-termination. Preliminary experiments to unit test several examples of C programs are very encouraging.

Many security protocols have the aim of authenticating one agent to another. Yet there is no clear consensus in the academic literature about precisely what "authentication" means. In this paper we suggest that the appropriate authentication requirement will depend upon the use to which the protocol is put, and identify several possible definitions of "authentication". We formalize each definition using the process algebra CSP, use this formalism to study their relative strengths, and show how the model checker FDR can be used to test whether a system running the protocol meets such a specification. 1 Introduction Many security protocols have appeared in the academic literature; these protocols often have the aim of achieving authentication, i.e., one agent should become sure of the identity of the other. The protocols are designed to succeed even in the presence of a malicious agent, called an intruder, who has complete control over the communications network, and so can intercept ...

Model checking approaches to the analysis of security protocols have proved remarkably successful. The basic approach is to produce a model of a small system running the protocol, together with a model of the most general intruder who can interact with the protocol, and then to use a state exploration tool to search for attacks. This has led to a number of new attacks upon protocols being discovered. However, if no attack is found, this only tells us that there is no attack upon the small system we modelled; there may be an attack upon some larger system. This is the question we consider in this paper: we prove that under certain conditions on the protocol and the environment in which it operates, if there is no attack upon a particular small system (with one honest agent for each role of the protocol) leading to a breach of secrecy, then there is no attack on any larger system leading to a breach of secrecy.

Many security protocols have appeared in the literature, with aims such as agreeing upon a cryptographic key, or achieving authentication. However, many of these have been shown to be flawed. In this paper we present a number of new attacks upon security protocols, and discuss ways in which we may avoid designing incorrect protocols in the future. 1. Introduction Many security protocols have appeared in the literature; these have various aims, such as agreeing upon a cryptographic key, or achieving authentication, where each agent becomes assured of the other's identity. Unfortunately, a large proportion of these protocols are subject to attacks, leading to them not correctly achieving their goals. In this paper, we present a few more attacks upon such protocols. The main point of this paper is to highlight the fact that, despite much research on the subject, many insecure protocols are still being produced. Further, most of the weaknesses that allow the attacks are well known. Our h...

A strand is a sequence of events; it represents either an execution by a legitimate party in a security protocol or else a sequence of actions by a penetrator. A strand space is a collection of strands, equipped with a graph structure generated by causal interaction. In this framework, protocol correctness claims may be expressed in terms of the connections between strands of different kinds.

We provide a method for deciding the insecurity of cryptographic protocols in presence of the standard Dolev-Yao intruder (with a finite number of sessions) extended with so-called oracle rules, i.e., deduction rules that satisfy certain conditions. As an instance of this general framework, we obtain that protocol insecurity is in NP for an intruder that can exploit the properties of the XOR operator. This operator is frequently used in cryptographic protocols but cannot be handled in most protocol models. We also apply our framework to an intruder that exploits properties of certain encryption modes such as cipher block chaining (CBC).

Cryptographic protocols are used in distributed systems to identify users and authenticate transactions. They may involve the exchange of about 2--5 messages, and one might think that a program of this size would be fairly easy to get right. However, this is absolutely not the case: bugs are routinely found in well known protocols, and years after they were first published. The problem is the presence of a hostile opponent, who can alter messages at will. In effect, our task is to program a computer which gives answers which are subtly and maliciously wrong at the most inconvenient possible moment. This is a fascinating problem; and we hope that the lessons learned from programming Satan 's computer may be helpful in tackling the more common problem of programming Murphy's.

This paper presents a general approach for analysis and verification of authentication properties in the language of Communicating Sequential Processes (CSP). It is illustrated by an examination of the Needham-Schroeder public-key protocol. The contribution of this paper is to develop a specific theory appropriate to the analysis of authentication protocols, built on top of the general CSP semantic framework. This approach aims to combine the ability to express such protocols in a natural and precise way with the facility to reason formally about the properties they exhibit. 1 Introduction Authentication comes in a number of flavours. For example, Gollmann [6] has identified four different varieties of authentication, which raises the question for any particular authentication protocol as to which kind of authentication the protocol was designed for, and which kinds it actually provides. The aim of the CSP approach is to reduce questions about security protocols and properties to ques...

We perform a systematic expansion of protocol narrations into terms of a process algebra in order to make precise some of the detailed checks that need to be made in a protocol. We then apply static analysis technology to develop an automatic validation procedure for protocols. Finally, we demonstrate that these techniques suffice for identifying a number of authentication flaws in symmetric key protocols such as Needham-Schroeder, Otway-Rees, Yahalom and Andrew Secure RPC.