Search

Many authentication and key exchange protocols are built using an accepted set of standard concepts such as Diffie–Hellman key exchange, nonces to avoid replay, certificates from an accepted authority, and encrypted or signed messages. We propose a general framework for deriving security protocols from simple components, using composition, refinements, and transformations. As a case study, we examine the structure of a family of key exchange protocols that includes Station-To-Station (STS), ISO-9798-3, Just Fast Keying (JFK), IKE and related protocols, deriving all members of the family from two basic protocols. In order to associate formal proofs with protocol derivations, we extend our previous security protocol logic with preconditions, temporal assertions, composition rules, and several other improvements. Using the logic, which we prove is sound with respect to the standard symbolic model of protocol execution and attack (the “Dolev–Yao model”), the security properties of the standard signature based Challenge-Response protocol and the Diffie–Hellman key exchange protocol are established. The ISO-9798-3 protocol is then proved correct by composing the correctness proofs of these two simple protocols. Although our current formal logic is not sufficient to modularly prove security for all of our current protocol derivations, the derivation system provides a framework for further improvements. [ABSTRACT FROM AUTHOR]

We propose a formal model of rational exchange and exchange protocols in general, which is based on game theory. In this model, an exchange protocol is represented as a set of strategies in a game that is played by the protocol parties and the network that they use to communicate with each other. Within this model, we give a formal definition for rational exchange and various other properties of exchange protocols, including fairness. In particular, rational exchange is defined in terms of a Nash equilibrium in the protocol game. We also study the relationship between rational and fair exchange, and prove that fairness implies rationality, but not vice versa. Finally, we illustrate the usage of our formal model for the analysis of existing rational exchange protocols by analyzing a protocol proposed by Syverson. We show that the protocol is rational only under the assumption that the network is reliable. [ABSTRACT FROM AUTHOR]

We carry forward the work described in our previous papers [5,18,20] on the application of data independence to the model checking of security protocols using CSP [19] and FDR [10]. In particular, we showed how techniques based on data independence [12,19] could be used to justify, by means of a finite FDR check, systems where agents can perform an unbounded number of protocol runs. Whilst this allows for a more complete analysis, there was one significant incompleteness in the results we obtained: while each individual identity could perform an unlimited number of protocol runs sequentially, the degree of parallelism remained bounded (and small to avoid state space explosion). In this paper, we report significant progress towards the solution of this problem, by means anticipated in [5], namely by “internalising” protocol roles within the “intruder” process. The internalisation of protocol roles (initially only server‐type roles) was introduced in [20] as a state‐space reduction technique (for which it is usually spectacularly successful). It was quickly noticed that this had the beneficial side‐effect of making the internalised server arbitrarily parallel, at least in cases where it did not generate any new values of data independent type. We now consider the case where internal roles do introduce fresh values and address the issue of capturing their state of mind (for the purposes of analysis). [ABSTRACT FROM AUTHOR]

Important properties of many protocols are liveness or availability, i.e., that something good happens now and then. In asynchronous scenarios, these properties depend on the scheduler, which is usually considered to be fair in this case. The standard definitions of fairness and liveness are based on infinite sequences. Unfortunately, this cannot be applied to most cryptographic protocols since one must restrict the adversary and the runs as a whole to length polynomial in the security parameter. We present the first general definition of polynomial fairness and liveness in asynchronous scenarios which can cope with cryptographic protocols. Furthermore, our definitions provide a link to the common approach of simulatability which is used throughout modern cryptography: We show that polynomial liveness is maintained under simulatability. As an example, we present an abstract specification and a secure implementation of secure message transmission with reliable channels, and prove them to fulfill the desired liveness property, i.e., reliability of messages. [ABSTRACT FROM AUTHOR]

During the last few years, a number of authenticated group key agreement protocols have been proposed in the literature. We observed that the efforts in this domain were mostly dedicated to the improvement of their performance in term of bandwidth or computational requirements, but that there were very few systematic studies on their security properties. In this paper, we tried to develop a systematic way to analyse protocol suites extending the Diffie‐Hellman key‐exchange scheme to a group setting and presented in the context of the Cliques project. This led us to propose a very simple machinery that allowed us to manually pinpoint several unpublished attacks against the main security properties claimed in the definition of these protocols (implicit key agreement, perfect forward secrecy, resistance to known‐key attacks). [ABSTRACT FROM AUTHOR]