Identity federations operating in a business or consumer context need to prevent the collection of user data across trust service providers for legal and business case reasons. Legal reasons are given by data protection legislation such as [1].Other reasons include business owners becoming increasingly aware of confidentiality risks that go beyond traditional information security, e.g., the numbers of authentications to an EDI service might provide insights into the volume of invoices, from which one could derive insider information. This paper proposes extended technical controls supporting three privacy requirements: a) Limited Linkability: Two service providers cannot link data related to a user without the help of a third party, using neither an identifier nor other identifying attributes like email addresses or payment data; b) Limited Observability: An identity provider cannot trace which services a user is using without the help of a third party; c) Non-Disclosure: Attributes provided to the service provider by an attribute provider are not disclosed to the identity provider or an intermediate service broker.Using a hub-and-spoke federation style following the privacy-by-design principle, this reference architecture addresses the privacy controls mentioned above.
In the real world, we usually identify persons by their appearance, voice, and so on. If this is not sufficient, identity cards are used. In the virtual world the situation is different. The basic concepts of the internet provide for unique identification of devices, not of their users. Hence, some kind of identity management system is required, which can be provided either by the state or by the private sector. Official electronic identity schemes, such as the Austrian Citizen Card, are being established in more and more countries. The carrier media of the Citizen Card is a smart card but, since 2009, the mobile phone signature is offered as a more comfortable alternative. However, much more widespread than that are simple user accounts with passwords, one for each individual service. This system has significant flaws. A solution can be provided by the concept of identity federation: an 'identity ecosystem' can be established in which a user can choose among several identity providers, authorise them to identify him towards service providers, authorise attribute providers to provide particular qualified user information to a service provider, etc. In this paper the different concepts mentioned above are elaborated and their interrelations and legal difficulties are described.
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