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Self-Sovereign Identity Primer

DIDs, verifiable credentials, and the W3C standards that try to put users — not platforms — in charge of digital identity.

30 min · advanced · part of Decentralized Identity & DePIN

The Identity Problem Crypto Tries to Solve

Most digital identity today is a rental agreement. Your Google account, your Facebook login, your bank's KYC profile, your government-issued ID number — none of them are really yours. They live on someone else's server, governed by someone else's terms of service, and they can be revoked, leaked, sold, or weaponized without your consent. When Equifax lost 147 million Americans' Social Security numbers in 2017, the affected users had no recourse and no ability to revoke the leaked data. When Twitter deplatforms an account, the user loses years of social proof that they cannot port elsewhere. When LinkedIn decides to rate-limit your profile, your professional reputation becomes their inventory. Self-sovereign identity (SSI) is the response. The core claim is that identity should be controlled by the subject — the actual person — rather than by an issuer or platform. You should hold your own credentials, present them selectively, and revoke them without asking permission. The technical primitives for this — Decentralized Identifiers (DIDs) and Verifiable Credentials (VCs) — are now W3C recommendations, meaning they are formally standardized rather than vaporware. Whether SSI will actually replace platform identity is an open question. The standards are real. The implementations are uneven. The user experience is still rough. And the dominant business model of the internet — surveillance advertising — has every incentive to keep identity locked inside walled gardens. But the infrastructure exists, several large deployments are running, and the regulatory tailwinds (eIDAS 2.0 in the EU, the EU Digital Identity Wallet rollout starting 2026) are pushing the industry toward credentials the user actually holds. This lesson is a technical primer on what DIDs and VCs actually are, what the major identity networks look like in 2025-2026, and what is real versus what is marketing.

Also in this lesson

  • 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.

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