Self-Sovereign Identity (SSI)

Self-sovereign identity (SSI) is a concept that puts individuals in control of their own digital identities without relying on a central authority. In traditional identity systems, such as government-issued IDs or online accounts, your identity is often stored and verified by third parties. SSI instead lets individuals hold signed credentials in a wallet of their own and share only the attributes a service needs, which the service can verify without contacting the issuer. Real-world implementations such as mobile Driver Licenses (mDL) and the European Digital Identity Wallet (EUDI Wallet) under the eIDAS 2.0 regulation (electronic identification, authentication and trust services) demonstrate the practical viability of SSI principles in government and regulatory contexts.

In an SSI system, users store their identity information in a secure Identity Wallet (also referred to as a digital wallet). This Identity Wallet is under their control, and they can choose when and with whom to share specific pieces of information. The integrity of what it holds comes from the issuer's digital signature; some systems additionally anchor identifiers on a blockchain or other ledger. This approach aims to enhance privacy, reduce the risk of identity theft, and give individuals more autonomy over their personal information in the digital domain.

Decentralized identity in the SSI model rests on seven elements:

  1. User Ownership and Control:
  • Individuals have Identity Wallets that store their identity information, such as personal details, credentials, and attributes.
  • Users have full control over their Identity Wallets, deciding what information to store and who can access it.
  1. Decentralized Identifiers (DIDs):
    • DIDs are a fundamental component of decentralized identity. They are unique identifiers created and owned by the individual.
    • DIDs are typically associated with public-private key pairs. The public key is shared openly, allowing others to verify the owner's identity, while the private key remains confidential and is used to sign and authenticate transactions.
  2. Verifiable Credentials:
    • Credentials such as driver's licenses or university degrees are issued by the responsible authority directly to the user's Identity Wallet as Verifiable Credentials (VCs), instead of being checked against the issuer's database at every use.
    • VCs are cryptographically signed, ensuring their authenticity and enabling users to selectively disclose them as needed.
  3. Decentralized Networks (Blockchain or Distributed Ledger Technology):
    • Some SSI systems use blockchain or other distributed ledger technologies to secure and timestamp identity transactions.
    • The decentralized nature of these networks enhances security and makes it difficult for a single point of failure or malicious actor to compromise the entire system.
  4. Selective Disclosure and Zero-Knowledge Proofs:
    • Users can selectively disclose only the necessary information for a particular transaction, preserving privacy.
    • Zero-knowledge proofs enable users to prove the validity of certain information without revealing the information itself.
  5. Interoperability:
    • SSI systems aim for interoperability, allowing users to use their digital identities across various platforms and services smoothly.
    • Specifications from W3C, the OpenID Foundation, ISO/IEC and the Decentralized Identity Foundation (DIF) define the shared credential formats and exchange protocols.
  6. Privacy by Design:
    • SSI systems prioritize privacy by minimizing the exposure of personal information and reducing the reliance on centralized databases, which are attractive targets for hackers.

Real-World Implementations

Mobile Driver License (mDL)

The mobile Driver License (mDL) is a practical implementation of SSI principles for government-issued identification. An mDL is a digital version of a physical driver's license stored in an Identity Wallet on a smartphone, standardized by ISO/IEC 18013-5.

Key features of mDL include:

  • Selective Disclosure: Users can share only the specific information required for a transaction (e.g., proving age without revealing the exact birthdate or address)
  • Cryptographic Security: Digital credentials are cryptographically signed by the issuing authority, making them tamper-evident and verifiable
  • Offline Verification: mDL supports offline verification scenarios, enabling identity checks without internet connectivity
  • Privacy-Preserving: Users maintain control over what information is shared and with whom
  • Standardization: Based on international standards (ISO 18013-5), ensuring interoperability across different jurisdictions and systems

The mDL demonstrates how SSI can transform traditional identity documents into user-controlled, privacy-preserving digital credentials while maintaining the same level of trust and security as physical documents.

EUDI Wallet and eIDAS 2.0 Regulation

The European Digital Identity Wallet (EUDI Wallet) is a key part of the European Union's eIDAS 2.0 regulation.

eIDAS 2.0 Overview: The updated Electronic Identification, Authentication and Trust Services (eIDAS) regulation, Regulation (EU) 2024/1183, requires every EU member state to offer its citizens a European Digital Identity Wallet by the end of 2026. The aim is one identity wallet that is accepted in every member state and by public and private services alike.

EUDI Wallet Capabilities:

  • Universal Access: All EU citizens, residents, and businesses will have the right to a European Digital Identity Wallet
  • Cross-Border Recognition: EUDI Wallets are recognized and accepted across all EU member states
  • Multi-Purpose Use: Supports both public services (e.g., accessing government services, filing taxes) and private sector applications (e.g., banking, telecommunications, travel)
  • Electronic Attestations of Attributes: Can store and present various types of verified credentials including identity documents, professional qualifications, educational certificates, and payment information
  • High Assurance Level: Meets stringent security and privacy requirements defined in the regulation
  • User Control: Users decide when and with whom to share their identity information, embodying SSI principles
  • Interoperability: Built on a common Architecture and Reference Framework (ARF) whose mandatory credential formats are ISO/IEC 18013-5 mdoc and SD-JWT VC (SD-JWT-based Verifiable Digital Credentials), exchanged over OpenID for Verifiable Credentials (OID4VC) protocols; DIDs are not required

Regulatory Impact: The eIDAS 2.0 regulation is a significant step toward making SSI mainstream, providing legal certainty and regulatory backing for digital identity solutions. It sets requirements for:

  • Very large online platforms to accept EUDI Wallets for user authentication
  • Minimum security and privacy standards for Identity Wallet providers
  • Technical standards for issuing, storing, and presenting digital credentials
  • Framework for trust service providers and relying parties

The EUDI Wallet shows SSI principles implemented at scale with regulatory backing, and other regions building privacy-preserving digital identity systems can take it as a reference.

SSI Architecture and Technical Standards

Self-Sovereign Identity provides the architectural framework and principles for decentralized identity management, while specific technical standards enable its implementation:

  • Decentralized Identifiers (DIDs): Provide persistent, cryptographically-verifiable identifiers that users control
  • Verifiable Credentials (VCs): W3C standard for representing and exchanging verifiable information (credentials, attestations, claims)
  • Identity Wallets: User-controlled applications for storing and managing DIDs and VCs
  • W3C Digital Credentials API: The browser-mediated channel through which a website requests a presentation from a wallet, and the point at which the wallet learns who is asking
  • Decentralized Networks: Optional infrastructure (blockchain, DLT) for anchoring DIDs and credential schemas

The combination of these standards enables the practical implementation of SSI principles. For detailed technical specifications on credential formats, issuance protocols (OID4VC), and privacy-preserving features, see the Verifiable Credentials article.

HolderIdentity walletIssuerVerifierVerifiable data registry controlsissuespresentspublishes keysresolves keys
The wallet is what makes the model self-sovereign: the credential sits with the person it describes, and the verifier checks it against a registry instead of calling the issuer back.

Summary

Self-Sovereign Identity gives individuals control over their digital identities, enhances privacy, and reduces reliance on central authorities for identity verification. It rests on cryptographic signatures and interoperable standards, particularly Verifiable Credentials and Decentralized Identifiers. Real-world implementations like mDL and the EUDI Wallet demonstrate the practical viability and regulatory acceptance of SSI principles in creating user-centric, privacy-preserving digital identity solutions.