This book has evolved out of roughly ve years of working on computing with social trust. In the beginning, getting people to accept that social networks and the relationships in them could be the basis for interesting, relevant, and exciting c- puter science was a struggle. Today, social networking and social computing have become hot topics, and those of us doing research in this space are nally nding a wealth of opportunities to share our work and to collaborate with others. This book is a collection of chapters that cover all the major areas of research in this space. I hope it will serve as a guide to students and researchers who want a strong introduction to work in the eld, and as encouragement and direction for those who are considering bringing their own techniques to bear on some of these problems. It has been an honor and privilege to work with these authors for whom I have so much respect and admiration. Thanks to all of them for their outstanding work, which speaks for itself, and for patiently enduringall my emails. Thanks, as always, to Jim Hendler for his constant support. Cai Ziegler has been particularly helpful, both as a collaborator, and in the early stages of development for this book. My appreciation also goes to Beverley Ford, Rebecca Mowat and everyone at Springer who helped with publication of this work.

Table of Contents Introduction to Computing with Social Trust Jennifer Golbeck The Need for Social Trust Challenges to Computing with Social Trust Future Questions Conclusions References Part I Models of Social Trust Examining Trust, Forgiveness and Regret as Computational Concepts Stephen Marsh and Pamela Briggs Introduction Why is Trust Important? Why a Formalization? A Parable of The Modern Age A Brief Sojourn to a¿¿Human Factors¿: Why Not Call it Trust After All Trust as Was What Can¿t Trust Give Us? Trust As Is, Part Zero: The Dark Side Distrust Mistrust Untrust Ignorance is The Continuum, Revisited Continuing a Difficult Relationship Regret What Regret Is The Many Faces of Regret Modeling Regret Trust as Is, Part One: Building Regret into Trust Forgiveness and The Blind and Toothless What Forgiveness Is A Model of Forgiveness Trust As Is, Part Two: The Incorporation of Forgiveness The Trust Continuum, Revised: The Limits of Forgiveness Applications: Revisiting the Parable and Imagining the Future The Parable at Work Regret Management Related Work Trust as Will Be: Future Work and Conclusions References A non-reductionist approach to trust Cristiano Castelfranchi, Rino Falcone, and Emiliano Lorini Introduction Desiderata for a logical model of social trust A logic for trust reasoning Syntax and semantics Axiomatization Possibility orders over formulas Execution preconditions for action execution A formal ontology of Trust Core trust Distrust, lack of trust and mistrust Delegation and decision to trust Comparative trust Conclusion References Social Trust of Virtual Identities Jean-Marc Seigneur Introduction Identity Terminology Computational Trust Terminology Flawed Trust Computation due to Simplistic Identity Approach Computational Trust under Identity Usurpation and Multiplicity Attacks Remaining ASUP Issues due to Identity Shortcomings Entification: Bridging Trust and Virtual Identities Recognition rather than Authentication End-to-End Trust Means for Recognition Adaptation Encouraging Privacy and Still Supporting Trust Accuracy and Attack-Resistance of the Trust Values Entification Framework Evaluation Trust Transfer Applied to the Email Domain ASUP Evaluation Conclusion References Part II Propagation of Trust Attack resistant trust metrics Raph Levien Introduction Attack resistance Redundant certification paths 3 Group trust metric Proof of attack resistance Implementation in Advogato Eigenvector trust metrics Stochastic model of PageRank Attack resistance of PageRank Advogato¿s eigenvector metric References On Propagating Interpersonal Trust ...