Formalizing and Managing Activity-Aware Trust in Collaborative Environments

Introduction

Distributed computing has evolved greatly in the last decade or so. Interactions between entities used to be mainly client-server or remote access. Recent years have seen a great increase in the kind and number of entities interacting, the patterns in which they interact, and the kinds of distributed services supporting these interactions. This ubiquitous use of distributed applications provides increased convenience, safety, and enjoyment for society. However, such applications and their users are vulnerable with respect to both the diversity of the principals providing these services and the interactions between them.

Consider the North American electric power grid, for instance, with nearly 3500 utility organizations (Force, 2004). These individually owned utility systems have been connected together to form interconnected power grids, which must be operated in a coordinated manner. There are many points of interactions among a variety of participants and a local change can have immediate impact everywhere. In order to detect disturbances that could escalate into cascading outages and take corrective actions, real-time information about the grid dynamics must be obtained to enhance the wide-area system observability, efficiency, and reliability. Unfortunately, as of today, power utilities are reluctant to disclose information in order to protect themselves financially and legally. Sharing of data might jeopardize their business due to their inability to quantify the risk regarding interactions with other grid participants. For example, unrestricted access to a utility’s data that are market-sensitive indicators could give a competitor an unfair advantage in adjusting its own contracts and prices. Similarly, a utility could distribute inaccurate data to mislead the other market participants. The “no sharing” policy could be relaxed under normal operating conditions if the risk of sharing were systematically contained by giving the participants the means to assess how trustworthy or not their potential and current collaborators are (Dionysiou et al., 2007).

Trust is a multifaceted concept, encompassing even more than message integrity, source authentication and reliance on other entities. While trust evaluation is an integral part of decision-making in collaborative models, there is no single correct way to determine the right level of trust, or which aspects to include. Decisions about how to weigh each facet lie with the evaluator and can differ substantially from situation to situation. This chapter presents and discusses a conceptual flexible trust framework that models an entity’s trust as a relation whose state gets updated as relevant conditions that affect trust change. The model allows entities to reason about the specification and adaptation of trust that is placed in an entity and the trust assessment of data that comes through nontrivial chains of processing. This chapter will discuss the motivation behind the new trust model, its design and its theoretical applicability in real-world scenarios; to be more specific the discussion will evolve around the following topics:

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  An analysis of the emerging need to address the dynamic and composable features of trust in open environments, especially in interactions which span multiple entities residing in different administrative domains

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  A set of requirements that must be met by any trust management system (TMS) in order to provide dynamic and composable trust in collaborative environments

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  A trust model that implements the above requirements to establish and manage trust relationships that correspond to a particular interaction, including:

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    A notation for specifying trust relationships that are tied not only to a narrow context but to a broader activity

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    An intuitive and practical approach that manages end-to-end trust assessment for a particular activity, where multiple trust relationships are systematically synthesized in a bottom-up evaluation manner

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    Extending the traditional concept of trust conditions into more expressive expectations that accommodate trust monitoring, where the expectation semantics incorporate not only expected values for particular trust requirements but also covering, aggregating, and triggering parameters that manipulate observed values.