A logic of authentication

Abstract

Questions of belief are essential in analysing protocols for the authentication of principals in distributed computing systems. In this paper we motivate, set out, and exemplify a logic specifically designed for this analysis: we show how various protocols differ subtly with respect to the required initial assumptions of the participants and their final beliefs. Our formalism has enabled us to isolate and express these differences with a precision that was not previously possible. It has drawn attention to features of protocols of which we and their authors were previously unaware, and allowed us to suggest improvements to the protocols. The reasoning about some protocols has been mechanically verified. This paper starts with an informal account of the problem, goes on to explain the formalism to be used, and gives examples of its application to protocols from the literature, both with shared-key cryptography and with public-key cryptography. Some of the examples are chosen because of their practical importance, whereas others serve to illustrate subtle points of the logic and to explain how we use it. We discuss extensions of the logic motivated by actual practice; for example, to account for the use of hash functions in signatures. The final sections contain a formal semantics of the logic and some conclusions.

A symbolic framework for multi-faceted security protocol analysis

“…it exploits information gathered from one protocol execution into another one, greatly enhancing its competence, and, for instance, cheating about identities. Hence, a clear specification of how protocol executions can be interleaved and of the security properties expected after such concurrent runs are necessary, as recognised for instance in [20].…”

“…This calls for verification models that are grounded on solid formal settings. Considerable success has already been achieved in the past years in approaching security protocol analysis and a variety of formal models and reasoning techniques have been developed to specify and verify their properties, (see [4,10,12,13,20,32,36,42,51,53] to cite a few). Many of these approaches have led to the development of automated verification toolkits.…”

Analysis of e-commerce protocols: Adapting a traditional technique

“…It seems that many protocols may be subject to the "arity" attack: our methods found that this attack is also possible on the Otway-Rees protocol (see [15] for a detailed description of the protocol and its analysis) and on the Yahalom protocol, as described in [7].…”

“…A seminal paper on logics of authentication is [7]. Work in this area has produced significant results in finding protocol flaws, but also appears to have limitations which will be hard to overcome within the paradigm.…”

On the decidability of cryptographic protocols with open-ended data structures

“…Using these methods, many flaws have been found in published protocols [14]. Most of these methods are based on the so-called Dolev-Yao model [18] -models such as special-purpose logics [12] or complexity theoretic and probabilistic models [7] are not discussed here.…”