Self-Sovereign Identity (SSI) is a novel identity model that empowers individuals with full control over their data, enabling them to choose what information to disclose, with whom, and when. This paradigm is rapidly gaining traction worldwide, supported by numerous initiatives such as the European Digital Identity (EUDI) Regulation or Singapore's National Digital Identity (NDI). For instance, by 2026, the EUDI Regulation will enable all European citizens to seamlessly access services across Europe using Verifiable Credentials (VCs). A key feature of SSI is the ability to selectively disclose only specific claims within a credential, enhancing the privacy protection of the identity owner. This paper proposes a novel mechanism designed to achieve Compact and Selective Disclosure for VCs (CSD-JWT). Our method leverages a cryptographic accumulator to encode claims within a credential into a unique, compact representation. We implemented CSD-JWT as an open-source solution and extensively evaluated its performance under various conditions. CSD-JWT provides significant memory savings, lowering usage by up to 46% compared to the state-of-the-art. It also minimizes network overhead by producing remarkably smaller Verifiable Presentations (VPs), with size reduction from 27% to 93%. Such features make CSD-JWT especially well-suited for resource-constrained devices, including hardware wallets designed for managing credentials.

In a world where digitalization isreshapingevery aspect of society, digital identity has become more crucial than ever to establish trust and accountability across all entities, whether human, organizational, or machine-based. Numerous initiatives are emerging worldwide, such as the United States mobile driver’s license (mDLs) and Singapore’s National Digital Identity (NDI). In May 2024, the European Union introduced Regulation 2024/1183, establishing the European Digital Identity Framework. By 2026, this framework will provide all European citizens with a European Digital Identity Wallet (EUDIW), allowing them to access both online and offline public and private services while maintaining full control over their data. Individuals can selectively disclose only the required information to access services. However, the current EUDIW design relies on Selective Disclosure for JSON Web Token (SD-JWT), which does not fully meet the privacy requirements outlined in the regulation. This paper presents a comprehensive comparison of the main selective disclosure mechanisms. Specifically, we identify relevant threat models, formalize associated security and privacy properties, and assess the extent to which existing mechanisms satisfy these properties in mitigating the identified threats. Furthermore, we introduce an open-source benchmark that evaluates multiple selective disclosure across key performance indicators, including computational latency, bandwidth consumption, and storage requirements.