Self-Sovereign Identity Primer

What you'll learn

• The Identity Problem Crypto Tries to Solve
• Decentralized Identifiers (DIDs)
• Verifiable Credentials (VCs)
• Worldcoin / World ID and Biometric Proof of Personhood
• EAS: The Ethereum Attestation Service
• Honest Assessment: What SSI Actually Solves

Key terms

Self-sovereign identity (SSI)

A model in which the subject of an identity — the actual person or organization — directly controls their identifiers and credentials, rather than relying on a centralized issuer or platform to store and grant access to them.

Decentralized Identifier (DID)

A globally unique identifier that does not require a centralized registration authority. Standardized by the W3C in June 2022 (DID Core 1.0). Resolves to a DID Document containing public keys and service endpoints controlled by the subject.

DID method

A specific implementation of the DID specification — `did:ethr` (Ethereum-anchored), `did:key` (self-contained), `did:web` (HTTPS-anchored), `did:ion` (Bitcoin-anchored via Microsoft ION). Over 150 methods are registered with W3C.

Verifiable Credential (VC)

A cryptographically signed claim about a subject, issued by an issuer and presentable by a holder to a verifier. Standardized by W3C VC Data Model 2.0. Three-party model: Issuer → Holder → Verifier.

Selective disclosure

A property of modern Verifiable Credentials that lets a holder reveal only specific parts of a credential — for example, proving "over 21" without revealing exact birthdate — using BBS+ signatures or zero-knowledge proofs.

World ID / Worldcoin

Proof-of-personhood credential issued by Tools for Humanity. Users scan their iris on a custom hardware Orb to receive a unique, anonymous cryptographic identifier. Over 10 million verifications across 35+ countries by mid-2025. Controversial — banned or restricted in Spain, Kenya, Hong Kong, and others.

EAS (Ethereum Attestation Service)

On-chain attestation primitive on Ethereum and L2s (Base, Optimism, Arbitrum). Anyone can define schemas and issue attestations signed by their Ethereum address. Underlies Coinbase Verifications on Base.

Proof of personhood (PoP)

A credential or system that proves the holder is a unique human being, without necessarily proving their identity. Important for sybil resistance, airdrops, and quadratic funding. Worldcoin, BrightID, and Gitcoin Passport / Passport XYZ are leading attempts.

eIDAS 2.0 / EUDI Wallet

EU regulation passed 2024 requiring all 27 member states to issue European Digital Identity Wallets to citizens. Built on W3C DIDs and Verifiable Credentials. Rollout begins 2026 — the largest production SSI deployment in the world.

Privado ID (formerly Polygon ID)

Identity protocol providing ZK-based verifiable credentials and DIDs, primarily on Polygon and other EVM chains. Renamed from Polygon ID in late 2024 as the project spun out of Polygon Labs.