Trust Models for Ubiquitous Mobile Systems

Trust Models for Ubiquitous Mobile Systems

Mike Burmester (Florida State University, USA)
DOI: 10.4018/978-1-60566-378-4.ch017
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This chapter introduces the notion of trust as a means to establish security in ubiquitous mobile network systems. It argues that trust is an essential requirement to enable security in any open network environments, and in particular, in wireless ad hoc environments where there is no network topology. In such environments, communication can only be achieved via routes that have to be trusted. In general it may be hard, or even impossible, to establish, recall, and maintain trust relationships. It is therefore important to understand the limitations of such environments and to find mechanisms that may support trust either explicitly or implicitly. We consider several models that can be used to enable trust in such environments, based on economic, insurance, information flow, and evolutionary paradigms.
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Trust In Wireless Mobile Networks

We consider environments in which there may be no fixed underlying network infrastructure, such as static base stations, for services such as packet routing, name resolution, node authentication, or the distribution of computational resources. In such environments, recalling and maintaining trust relationships is particularly challenging. Mobile systems share many of the complexities of fixed infrastructure systems. For example, nodes may have (Burmester & Yasinsac, 2004):

  • 1.

    No prior relationship or common peers

  • 2.

    No shared proprietary software

  • 3.

    Different transmission, memory and processing capabilities

  • 4.

    Different mobility characteristics

  • 5.

    Different lifetime properties

Defining Trust

Trust is a highly abstract concept and it is unlikely that any simple definition can comprehensively capture all the subtleties of its essence. Informally we may define trust as a behavioral expectation of one party toward another. There are two perspectives in this definition, one in which a party awards trust to another (Alice trusts that Bob’s public key is PK(Bob)), the other in which a party gains trust from another (Alice has convinced Bob that her public key is PK(Alice)).

Representing Trust: Certificates vs. Tokens

In any stateful trust model, trust must be represented by some type of persistent structure. Certificates are the de facto standard for representing trust relationships that are protected by cryptography. Certificates are portable and bind a cryptographic key (a digital string) to an entity, thus guaranteeing the authenticity of actions performed by that entity. Trust tokens are another structure that can be used to represent trust in a more direct way, analogous to the relation between checks and cash. Checks guarantee payment by tying the purchaser to some identifying information (like a certificate), while the value of cash is self-contained.

Trusted Third Parties

A trusted third party (TTP) can facilitate significantly the establishment of trust in mobile environments. For example, if two parties A and B who do not know each other have a trust relationship with a third party T, then T can be an effective intermediary for transactions between A and B. However in general, wireless mobile networks may not have any infrastructure components that are typically used as TTPs. In such cases, TTPs have to be elected or assigned by using an appropriate election or assignment protocol.

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