Privacy enhancing technologies (PETs) allow to achieve user’s transactions unlinkability across different online Service Providers. However, current PETs fail to guarantee unlinkability against the Identity Provider (IdP), which becomes a single point of failure in terms of privacy and security, and therefore, might impersonate its users. To address this issue, OLYMPUS EU project establishes an interoperable framework of technologies for a distributed privacy-preserving identity management based on cryptographic techniques that can be applied both to online and offline scenarios. Namely, distributed cryptographic techniques based on threshold cryptography are used to split up the role of the Identity Provider (IdP) into several authorities so that a single entity is not able to impersonate or track its users. The architecture leverages PET technologies, such as distributed threshold-based signatures and privacy attribute-based credentials (p-ABC), so that the signed tokens and the ABC credentials are managed in a distributed way by several IdPs. This paper describes the Olympus architecture, including its associated requirements, the main building blocks and processes, as well as the associated use cases. In addition, the paper shows how the Olympus oblivious architecture can be used to achieve privacy-preserving M2M offline transactions between IoT devices.

The growing availability of mobile devices has lead to an arising development of smart cities services that share a huge amount of (personal) information and data. Without accurate and verified management, they could become severe back-doors for security and privacy. In this paper, we propose a smart city infrastructure able to integrate a distributed privacy-preserving identity management solution based on attribute-based credentials (p-ABC), a user-centric Consent Manager, and a GDPR-based Access Control mechanism so as to guarantee the enforcement of the GDPR’s provisions. Thus, the infrastructure supports the definition of specific purpose, collection of data, regulation of access to personal data, and users’ consents, while ensuring selective and minimal disclosure of personal information as well as user’s unlinkability across service and identity providers. The proposal has been implemented, integrated, and evaluated in a fully-fledged environment consisting of MiMurcia, the Smart City project for the city of Murcia, CaPe, an industrial consent management system, and GENERAL_D, an academic GDPR-based access control system, showing the feasibility.

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Lack of standardization and the subsequent difficulty of integration has been one of the main reasons for the scarce adoption of privacy-preserving Attribute-Based Credentials (p-ABC). Integration with the W3C's Verifiable Credentials (VC) specification would help by encouraging homogenization between different p-ABC schemes and bringing them all closer to other digital credentials.What is more, p-ABCs can help to solve privacy issues that have been identified in applications of VCs to use cases like vaccination passports. However, there has not been much work focusing on the collaboration between p-ABCs and VCs. We address this topic by establishing initial steps for extra standardization of elements that will help with the integration of p-ABCs into the standard. Namely, we propose a data model for predicates, which are a staple of p-ABC systems, and tools and guidelines to ease the adaptation process like a validation meta-schema. These ideas have been applied in a proof-of-concept implementation of the OLYMPUS distributed p-ABC scheme paired with serialization following the VC data model. CCS Concepts: • Security and privacy → Pseudonymity, anonymity and untraceability.

This paper summarizes the contents and presentations held at a workshop at the IFIP Summer School on Privacy and Identity Management 2021, focusing on privacy-preserving identity management. In this document, we first introduce the necessary background on privacypreserving identity management, including core cryptographic concepts. We then present a demonstrator scenario which benefits from the use of such technologies. Finally, we present a distributed privacy-preserving identity management framework offering an even higher level of security and privacy than previous work.

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Identity Management (IdM) systems have traditionally relied on a centralized model prone to privacy, trust, and security problems, like potential massive data breaches or identity spoofing. Identity providers accumulate excessive power that might allow them to become a big brother, analyzing and storing as much data as possible. Users should be able to trust identity providers and manage their personal information straightforwardly without compromising their privacy. The European OLYMPUS project introduces a distributed approach for IdM based on enhanced Attribute-Based Credentials (ABC) that splits the role of Identity Provider to limit their influence and chances to become a unique point of failure. However, the trust relationship between service providers, users, and identity providers is still a gap in those kinds of privacy-preserving ABC systems. Decentralized technologies are an opportunity to break away from the centralized model and propose systems that respect privacy while increasing users' trust. This paper presents an evolution of the OLYMPUS architecture, maintaining all the privacy features and incorporating distributed ledger technologies to enhance trust and security in online transactions and IdM systems. The proposed system has been implemented, tested, and validated, showing its performance and feasibility to manage user's identity in a fully privacy-preserving, distributed and reliable way.