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User centricity is a significant concept in federated identity management (FIM), as it provides for stronger user control and privacy. However, several notions of user-centricity in the FIM community render its semantics unclear and hamper future research in this area. Therefore, we consider user-centricity abstractly and establish a comprehensive taxonomy encompassing user-control, architecture, and usability aspects of user-centric FIM. On the systems layer, we discuss user-centric FIM systems and classify them into two predominant variants with significant feature sets. We distinguish credential-focused systems, which advocate offline identity providers and long-term credentials at a user's client, and relationship-focused systems, which rely on the relationships between users and online identity providers that create short-term credentials during transactions. Note that these two notions of credentials are quite different. The further one encompasses cryptographic credentials as defined by Lysyanskaya et al. [30], the latter one federation tokens as used in today's FIM protocols like Liberty.We raise the question where user-centric FIM systems may gowithin the limitations of the user-centricity paradigm as well as beyond them. Firstly, we investigate the existence of a universal user-centric FIM system that can achieve a superset of security and privacy properties as well as the characteristic features of both predominant classes. Secondly, we explore the feasibility of reaching beyond user-centricity, that is, allowing a user of a user-centric FIM system to again give away user-control by means of an explicit act of delegation. We do neither claim a solution for universal user-centric systems nor for the extension beyond the boundaries † Work performed during an internship at the IBM Zurich Research Laboratory in Switzerland.* Part of the work reported in this paper is supported by the European Commission through the IST Project PRIME. The PRIME project receives research funding from the European Community's Sixth Framework Programme and the Swiss Federal Office for Education and Science.Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. of user-centricity, however, we establish a starting point for both ventures by leveraging the properties of a credential-focused FIM system.

An emerging approach to the problem of reducing the identity theft is represented by the adoption of biometric authentication systems. Such systems however present however several challenges, related to privacy, reliability, security of the biometric data. Inter-operability is also required among the devices used for the authentication. Moreover, very often biometric authentication in itself is not sufficient as a conclusive proof of identity and has to be complemented with multiple other proofs of identity like passwords, SSN, or other user identifiers. Multi-factor authentication mechanisms are thus required to enforce strong authentication based on the biometric and identifiers of other nature.In this paper we provide a two-phase authentication mechanism for federated identity management systems. The first phase consists of a two-factor biometric authentication based on zero knowledge proofs. We employ techniques from vector-space model to generate cryptographic biometric keys. These keys are kept secret, thus preserving the confidentiality of the biometric data, and at the same time exploit the advantages of a biometric authentication. The second authentication combines several authentication factors in conjunction with the biometric to provide a strong authentication. A key advantage of our approach is that any unanticipated combination of factors can be used. Such authentication system leverages the information of the user that are available from the federated identity management system.

We develop solutions for the security and privacy of user identity information in a federation. By federation we mean a group of organizations or service providers which have built trust among each other and enable sharing of user identity information amongst themselves. We first propose a flexible approach to establish a single sign-on (SSO) ID in the federation. Then we show how a user can leverage this SSO ID to establish certified and un-certified user identity attributes without the dependence on PKI for user authentication. This makes the process more usable and privacy preserving. Our major contribution in this paper is a novel solution for protection against identity theft of these identity attributes. We provide protocols based on cryptographic techniques, namely zero knowledge proofs and distributed hash tables. We show how we can preserve privacy of the user identity without jeopardizing security. We formally prove correctness and provide complexity results for our protocols. The complexity results show that our approach is efficient. In the paper we also show that the protocol is robust enough even in case semi-trusted "honest-yet curious" service providers thus preventing against insider threat. In our analysis we give the desired properties of the cryptographic tools used and identify open problems. We believe that the approach represents a precursor to new and innovative cryptographic techniques which can provide solutions for the security and privacy problems in federated identity management.

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