Crypto glossary

Self-Sovereign Identity

Self-sovereign identity (SSI) is an approach in which you hold your own digital identity and credentials, such as a diploma or proof of age, in a wallet you control, and share them directly with whoever needs to check them, without a central platform in the middle.

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The problem it tries to solve

Today most online identity is borrowed. You log in with an account that a company owns, and your personal data sits in many separate databases, each a potential leak. If the provider closes your account, that identity is gone. Self-sovereign identity reverses the direction: the person holds the credentials and decides what to share, while organisations only verify them.

The idea was popularised in 2016 by Christopher Allen, who set out ten principles including control, portability, consent and minimal disclosure.

How it works

SSI involves three roles. An issuer, such as a university or government agency, signs a digital credential. The holder keeps it in an identity wallet. A verifier, such as an employer or website, checks the issuer's signature without calling the issuer.

Two W3C standards do most of the work. Decentralized identifiers (DIDs) are addresses that point to public keys the holder controls, sometimes anchored on a blockchain. Verifiable credentials are the signed statements themselves. Personal data stays in the holder's wallet, not on a public chain; at most, issuers' public keys or revocation lists are published there.

An example

Say an online service must confirm you are over 18. Instead of uploading a photo of your passport, you present a credential your government issued, and with selective disclosure or a zero-knowledge proof you reveal only the statement that you are over 18, not your name, birth date or address. The service checks the signature and the credential's revocation status and lets you in.

Limits and risks

Control comes with responsibility. If you lose the keys to your identity wallet and there is no recovery method, you may need every issuer to reissue your credentials. A credential is only as trustworthy as its issuer, so SSI does not remove the need for trusted institutions; it changes how their statements travel. Reusing the same identifier everywhere can also let services link your activity together. Adoption is still uneven, although the EU's revised eIDAS regulation, adopted in 2024, requires member states to offer citizens a digital identity wallet built on similar ideas.

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Frequently asked questions

Is self-sovereign identity stored on a blockchain?

Personal data should not be. A blockchain may hold identifiers, public keys or revocation registries, while the credentials themselves stay in the holder's wallet.

What is the difference between SSI and decentralized identity?

The terms overlap heavily. Self-sovereign identity stresses the principle of user control, while decentralized identity usually refers to the technical building blocks such as DIDs.

Can SSI replace KYC checks?

It can make them reusable and less invasive, for example by sharing a verified credential instead of documents, but a regulated party still has to trust the issuer and follow its legal duties.

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