Propagating Trust and Privacy Aspects in Federated Identity Management Scenarios

This paper presents a trust-management application for trust based relationships in federated identity management (FIM). It empowers discovery, technical interpretation of the meaning of trust, dynamic calculation of trust levels and afterwards static composition of trustworthy relationships between Identity and Service providers, which can be accomplished through the use of servicespecific XACML policies to enforce the required trust and privacy aspects. 1 The Problem Statement Nowadays most of the emerging approaches to digital identity management have been developed to address the distributed user data management problem, by providing the feature of the federation process while each partner service has its own privacy constraints and security policies. In addition to deciding what right each user has to access a Service Provider (SP), it is also possible to the user to decide if he wants to access this service provider without re-authentication. The condition to enable this right is that the user must authenticate at an Identity Provider (IDP) who is recognised and accepted by the SP. Therefore, providing efficient and seamless interrelationship between IDPs and SPs in inter-organization scenarios, based on FIM, requires building trust-based relationships that enable IDPs to securely distribute the user’s identity information, and the SP to manage and control the access set to the services it provides. Consequently, those trust relationships, which allow identity and policy information to flow between the participating SPs, need to be formed quickly and efficiently to maximize productivity and eliminate the manual processes that often take place nowadays. In today’s federations, trust between IDPs and SPs is typically established on a contractual basis and thus quite static by building the so-called trust communities. The other technical aspects of trust are limited to authenticating and authorizing users, but secure FIM systems should not only authenticate users, but also allow them to delegate their rights and beliefs to other users securely. However, we want to achieve more dynamic trust relationships and especially involve the aspects of reputation management which allow the peer to reflect its own experience as well as the experience of other known peers with the new peer; and thus building dynamic trust relationships based on recommendations of other peers, as considering the human factors beside the technical aspects is more and more becoming a crucial question. The objective of this work is to build such trust relationships between group of peers, within organizations, who meet the trust requirements through individual experience and sharing experiences with other peers with similar preferences, as most of the answers to such issues often depend on whether the peer we want to communicate with, is someone inside or outside the organization and also depends on how a set of organizations can be defined in connection with the IDP and the SP in FIM. This issue relate, more precisely, to designing an appropriate algorithm for dynamically computing and interpreting the value representing the trust level between the peers. Therefore, the algorithm will be based on a collection of attributes that are basically created, along with an identity of the peer, during a process of the interaction, as they tend to identify the other party as well as the level of trust in order to estimate carefully how it is likely to behave in a given situation depending on the rewards for being trustworthy. In the second stage of our solution, the outputs of the algorithm can be afterwards useful in the policy-based privacy rules for constructing an efficient threshold decision point, as it is the case in many FIM-Scenarios that the users’ data can be only released if a certain threshold of the trust level is exceeded. The rest of the paper is organized as follows: Section 2 introduces a detailed analysis to the requirements on the IDP as well as on the SP side that may occur in our trust model. In section 3 we explain our solution based on the recursive trust algorithm, including the acquaintance graph and the different related mechanisms and aspects that may be integrated within the proposed algorithm to provide the desired trust model. Section 4 provides an analysis about the LDAP schema and the DIT definition that will help define the trust relationships among the principals. Implementation analysis as well as evidence will conclude this section. Section 5 provides an overview of the state of the art and similar approaches for estimating the value of trust. Finally Section 6 concludes the current status and discusses future research directions. 2 Requirement analysis of trust in Federated Identity Management Usually the main kinds of peers known as principals connected by those trust relationships are based on their particular identity lifetimes: people who can make assertions affiliated to their long-lived IDs; computers can make close evidence of correct operation from their IP-Addresses; and organizations are generally a set of people and computers and can benefit from this collection to build trust relationship. The Credentials describe each kind of principal, often as attributes attached to that principal and its relationships to other principals [8]. The focus of this solution is to figure out the way appropriate correspondent can be selected, when calculating the trust level according to the user’s respectively the Service Provider’s trust requirements. This approach for modelling trust is realised as an algorithm in defining, representing, calculating, and propagating the value of trust from which we can quantitatively read the relationship of any two entities in our Framework. While collecting all the necessary requirements for the trust calculation algorithm, it is primordial to investigate the following issues on the IDP side as well as on the SP side: The user identity mapping which allows SPs to correlate personal information about the user in a way that otherwise would not be possible. When the IDP consents to identity mapping, the SP must accept a given policy for how mapping can be used to correlate data linked to the different identities in the corresponding IDP. Consequently, the SP’s failure to adhere to the privacy policy for identity mapping can cause distrust. Validation of SP’s term of use, privacy policies, shipping conditions, as stated and agreed in the formal contract and service level agreements. Previous experience with the service and with other services within the same SP. Trust and confidence of other users (for example within the same IDP) in that SP. 2.1 Requirements of the Service Provider on the users and their Identity Provider On the one hand service provider provides services for end users, and on the other hand they act as a relying party to validate credentials issued by a trusted identity partner, on the basis of which they provide services to that trusted identity. Trust can be established for users and Identity Providers through assurances that they follow the recommended practices of the SP for handling authentication credentials with adequate care, and by having a history with the service provider that is free of security incidents. The SP, consequently, may require investigations, for instance on: The way credentials are issued to the users and whether the IDP has implemented adequate procedures for registering users and for issuing their credentials in a trustful way. Experience of the SP with the user, for instance experience on having a history without registration error because of unpaid bill or delivery rejections. Experience of the SP with the users’ IDP. Rating and opinions of other known Service Providers about the concerned IDP.