Self-Sovereign Identity Glossary

This glossary gives a (very) quick overview of the significant actors, roles, and components of a fully-realized Self-Sovereign Identity (SSI) solution.

For more formal definitions, please see https://www.w3.org/TR/vc-data-model/#terminology

Components

Verifiable Credential (VC)

A credential which has been generated about a given individual entity (Subject) by an Issuer. A credential is formed as a collection of attributes (or ‘claims’) that describe qualities of the subject. A Verifiable Credential is signed by its Issuer, allowing the receiver of a presentation of that VC (Verifier) to cryptographically prove that the credential was indeed issued by the Issuer the VC indicates.

Zero-Knowledge Proof (ZKP)

A process through which ownership of a piece of information is proved without revealing the information itself. This allows the ability for a Verifier to request responses to queries such as “Prove you are over 18”, without the Holder having to release a VC which states a Subject’s age or birthdate.

Verifiable Data Registry

The location in which the schema and key information relating to a given Verifiable Credential is stored. For example, an Issuer’s public keys, used by a Verifier when validating a presented VC. In the fully-decentralized world of SSI, this data is stored on an Immutable Public Ledger.

Wallet

The location a Holder stores their VCs. This could be on a hardware device a Holder owns (e.g. an app on their mobile phone) or a ‘web wallet’, available

Agent

The software that communicates between Holders, Verifiers, and Issuers using the necessary protocols. A Holder’s Wallet will often comprise a built-in agent.

Immutable Public Ledger

A location accessible to all involved Actors, assured to be resistant to tampering. Most commonly this is considered to be a public blockchain.

Actors / Roles

Holder

The entity to which VCs are issued by an Issuer, and from which a Verifier requests presentations. Holder’s generally own (or have access to) a Wallet in which they store their credentials. A Holder is often, but not always, the Subject to which the VCs in their Wallet refer.

Subject

An individual entity about which claims can be made which can be formed into VCs; e.g., a person, service, or device.

Issuer

An entity that issues VCs to a Holder, by communicating a VC to them and ensuring the necessary information to verify that VC is available in a Verifiable Data Registry.

Verifier

An entity that requests a presentation of a VC from a Holder. Note: A single entity may concurrently be a Subject, Holder, Issuer, and Verifier.

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