A Systematisation of Knowledge: Connecting European Digital Identities with Web3

TL;DR

This paper argues that ambiguity between decentralised identity and self-sovereign identity persists under EU eIDAS 2.0 and conducts a 2005–2024 state-of-the-art review to diagnose the divergence between OpenID Connect-based identity and Web3/DLT approaches. It shows that regulatory technology (ARF/eIDAS 2.0) largely excludes public-permissionless ledgers, necessitating an interoperability bridge between OIDC-based EUDIWs and Web3 applications. The authors propose a privacy-preserving bridging architecture that stores cryptographic keys on-device while encrypting credentials in cloud storage and using predicate-based attestations to align Web3 with European identity standards. The work highlights policy and technical gaps, offering a pathway for bridging standards, reducing privacy risks, and enabling Web3–EU digital identity interoperability, while noting limitations and areas for further research on crypto-agility and trust models.

Abstract

The terms self-sovereign identity (SSI) and decentralised identity are often used interchangeably, which results in increasing ambiguity when solutions are being investigated and compared. This article aims to provide a clear distinction between the two concepts in relation to the revised Regulation as Regards establishing the European Digital Identity Framework (eIDAS 2.0) by providing a systematisation of knowledge of technological developments that led up to implementation of eIDAS 2.0. Applying an inductive exploratory approach, relevant literature was selected iteratively in waves over a nine months time frame and covers literature between 2005 and 2024. The review found that the decentralised identity sector emerged adjacent to the OpenID Connect (OIDC) paradigm of Open Authentication, whereas SSI denotes the sector's shift towards blockchain-based solutions. In this study, it is shown that the interchangeable use of SSI and decentralised identity coincides with novel protocols over OIDC. While the first part of this paper distinguishes OIDC from decentralised identity, the second part addresses the incompatibility between OIDC under eIDAS 2.0 and Web3. The paper closes by suggesting further research for establishing a digital identity bridge for connecting applications on public-permissionless ledgers with data originating from eIDAS 2.0 and being presented using OIDC.