Key Technologies in Self-Sovereign Identity (SSI)

Self-Sovereign Identity (SSI) relies on a combination of emerging and established technologies to realize its vision of user-controlled digital identity, as outlined in Exploring Self-Sovereign Identity (SSI). These technologies provide the building blocks for creating, managing, and using digital identities in a decentralized, secure, and privacy-preserving manner, adhering to the Core Principles of SSI. The two most fundamental technologies are Decentralized Identifiers (DIDs) and Verifiable Credentials (VCs).

Abstract image of interconnected technological building blocks or puzzle pieces.
The core technological components that enable SSI.

Decentralized Identifiers (DIDs)

Decentralized Identifiers (DIDs) are a new type of identifier that enables verifiable, decentralized digital identity. A DID refers to any subject (e.g., a person, organization, thing, data model, abstract entity, etc.) and is designed to be globally unique, resolvable with high availability, and cryptographically verifiable.

  • User Control: DIDs are controlled by their subject, independent of any centralized registry, identity provider, or certificate authority.
  • Decentralization: While some DID methods might use centralized systems as part of their infrastructure, the control over the DID itself remains decentralized. Many DIDs leverage distributed ledger technology (DLT) or blockchains for anchoring. Understanding core DLT concepts can be helpful here, see Understanding Blockchain Technology for more.
  • Cryptographic Verifiability: DIDs are associated with cryptographic key pairs, allowing the DID controller to prove control over the DID by signing messages with the private key.
  • DID Documents: When a DID is resolved, it returns a DID Document. This document contains information associated with the DID, such as cryptographic keys for authentication, service endpoints for interaction, and other metadata.

DIDs are the foundation for creating persistent, portable, and secure digital identities that are not reliant on any single organization.

Verifiable Credentials (VCs)

Verifiable Credentials (VCs) are digital versions of the physical credentials we use every day, like driver's licenses, university diplomas, or membership cards. They are statements (claims) made by an issuer about a subject (the holder of the credential), in a way that is cryptographically secure, privacy-respecting, and machine-verifiable.

  • Tamper-Evident: VCs are digitally signed by the issuer, making them tamper-evident. Any alteration to the credential after issuance would invalidate the signature.
  • Holder Control: The holder (subject) of the VC stores it (often in a digital wallet) and has control over when and with whom it is shared.
  • Selective Disclosure: Advanced VCs can support selective disclosure, allowing the holder to reveal only necessary pieces of information from a credential, rather than the entire credential. For example, proving you are over 18 without revealing your exact birth date.
  • Verification: A verifier (a party that needs to check a credential) can cryptographically verify the authenticity and integrity of the VC, as well as the identity of the issuer, often without needing to directly contact the issuer at the time of verification.

VCs, in conjunction with DIDs, allow for trustworthy and secure sharing of identity attributes and attestations. The structure and security of VCs are critical, much like the security considerations in Mastering Containerization with Docker and Kubernetes for software deployment.

Conceptual image of secure digital credentials or certificates.
Verifiable Credentials act as secure and trustworthy digital attestations.

Other Supporting Technologies

While DIDs and VCs are central, other technologies play important roles in the SSI ecosystem:

  • Digital Wallets: Secure software applications used by individuals to store and manage their DIDs, VCs, and cryptographic keys.
  • Distributed Ledger Technologies (DLTs) / Blockchains: Often used as a decentralized, censorship-resistant layer for anchoring DIDs, DID Documents, VC schemas, or revocation registries.
  • Cryptographic Algorithms: The underlying mathematics (e.g., public-key cryptography, digital signatures, zero-knowledge proofs) that provide the security and verifiability for SSI components.
  • Communication Protocols: Secure and private messaging protocols for interactions between identity actors (issuers, holders, verifiers), such as DIDComm.

The interplay of these technologies aims to create a robust and user-centric identity layer for the internet. As these technologies mature, we can expect to see more innovative Real-World Use Cases of SSI emerge.

Diagram showing the interaction of various SSI technologies like DIDs, VCs, and Wallets.
The ecosystem of technologies that support and enable SSI functionalities.