Formalising theories of trust for authentication protocols

Abstract

This paper discusses a formal approach for establishing theories of trust for authentication systems which can be used to reason about how agent beliefs evolve through time. The goal of an authentication system is to verify and authorise users in order to protect restricted data and information, so trust is a critical issue for authentication systems. After authentication, two principals (people, computers, services) should be entitled to believe that they are communicating with each other and not with intruders. So, it is important to express such beliefs precisely and to capture the reasoning that leads to them. In this paper, we focus on analysis of agent beliefs in dynamic environments using a temporalised belief logic, obtained by adding a temporal logic onto a belief logic. Working through a well-known authentication protocol, namely Kerberos, we discuss how to express principal beliefs involved in authentication protocols and the evolution of those beliefs based on a series of observations of agents as a consequence of communication. Our approach could be used for designing, verifying and implementing authentication protocols.

A MAS-based infrastructure for negotiation and its application to a water-right market

“…First, the mediator must be aware of the current context of application that may allow or forbid the opening of a particular type of negotiation process. Second, the mediator needs to take into consideration the user's reputation and/or trust properties to decide about the opening [18,22]. According to all this information, the mediator decides about accepting or declining the offer to open the new negotiation.…”

A Temporalised Belief Logic for Reasoning about Authentication Protocols

“…A trust theory for a given authentication system consists of a set of rules which can be used for reasoning about agent beliefs and security properties that the system may satisfy [13].…”

An analytic tableau calculus for a temporalised belief logic

“…We can refer to the property by nested applications of first and next as follows: first next n ϕ where next n is the n-folded application of next. We have also found this feature quite useful in the formalization of certain properties in authentication protocols such as those that state something occurred at a specific point in time [35,36].…”

“…MEL is more restrictive than TML in that nested belief modalities are not allowed in the logic, however, it is able to model agent beliefs as they are revealed through communication between agents. Similarly, we restrict ourselves to a multi-modal variant of KD because we have found that it is sufficient for representing the basic notions in the authentication (and communication) protocols we have studied [35,36], such as a message has been received from another agent, the message is believed to be reliable and/or authenticated. The protocols do not require any special condition for agent beliefs, other than the requirement that the agents are rational.…”

“…For instance, it has been shown that the fibring of TML and SLTL may lead to a combined logic in which the temporal and modal operators can be applied without any restrictions [31,41]. However, fibring is in general a much more complex combination technique than temporalisation, and, as we have demonstrated in our earlier work [35,36], temporalised logics are usually expressive enough for the specification and verification of security protocols. Moreover, a recent work by Franceschet et al [16] proposed a model checking procedure which could be used to develop model checkers for temporalised logics based on the model checking procedures for the component logics.…”