Self-sovereign identity (SSI) is a digital identity model in which individuals hold and control their own identity data, usually as verifiable credentials stored in a digital wallet on their device, and present cryptographic proofs of those credentials directly to the parties that need them. In digital identity and privacy, SSI moves control away from central identity providers and toward the person the data describes.
In conventional models, a person proves identity by logging in through an account at a platform or by letting a verifier query a central database. SSI replaces this with a trust triangle: an issuer signs a credential, the holder keeps it, and a verifier checks the signature without contacting the issuer each time. The approach aims to reduce data collection, correlation and dependence on any single provider.
How self-sovereign identity works
SSI relies on public-key cryptography and three roles. An issuer, such as a government agency, university or bank, creates a credential about the holder and signs it with its private key. The holder stores the credential in a wallet. A verifier receives a presentation from the holder and checks the issuer’s signature using the issuer’s public key.
| Element | Role | Example |
|---|---|---|
| Issuer | Attests facts about a person and signs credentials | Ministry issuing a digital identity card |
| Holder | Stores credentials and decides what to share | Citizen with a wallet app |
| Verifier | Requests and checks proofs | Online shop checking age |
| Digital wallet | Software that keeps keys and credentials | Mobile identity wallet |
| Verifiable data registry | Publishes public keys, schemas and revocation status | Trust list or distributed ledger |
Identifiers in SSI are often Decentralized Identifiers (DIDs), a W3C standard for identifiers that resolve to documents containing public keys without requiring a central registration authority. Credentials commonly follow the W3C Verifiable Credentials data model or formats such as SD-JWT and the ISO mobile document format used for mobile driver’s licenses.
Core principles of self-sovereign identity
SSI is defined as much by its principles as by its technology. A widely cited set of ten principles from 2016 frames the person as the owner and controller of their identity, and most later frameworks build on it.
| Principle | What it means | Practical expression |
|---|---|---|
| Control | The person decides how their identity is used | Holder approves every presentation |
| Consent | No data is shared without agreement | Explicit prompts in the wallet |
| Minimization | Only the necessary data is disclosed | Selective disclosure and predicates |
| Portability | Identity is not locked to one provider | Credentials move between wallets |
| Persistence | Identity lasts as long as the person wants | Identifiers not revoked by a platform |
| Interoperability | Credentials work across systems and borders | Shared standards and trust frameworks |
In practice no deployed system fulfills every principle completely. Government-issued credentials, for example, still depend on the issuer’s authority, and the issuer can revoke them. SSI therefore describes a spectrum of user control rather than absolute independence.
Privacy features: selective disclosure and unlinkability
The main privacy benefit of SSI is data minimization at the moment of sharing. Instead of handing over a whole document, the holder reveals only the attributes a verifier needs, a technique called selective disclosure.
Advanced schemes go further with predicate proofs, which prove a statement such as being over 18 without revealing the birth date, and with unlinkable presentations, which prevent verifiers from recognizing the same credential across visits. Formats differ in this respect: hash-based selective disclosure hides attributes but can leave signatures that act as correlation handles, while zero-knowledge signature schemes such as BBS aim to remove them.
Privacy also depends on the verification flow. When verifiers check signatures and revocation status without contacting the issuer, the issuer learns nothing about where a credential is used, which avoids the phone-home problem of some centralized login systems.
Self-sovereign identity compared with other identity models
SSI is one stage in the evolution of digital identity models. The differences concern who stores the data, who sees each use and who can cut off access.
| Model | Where identity data lives | Who sees each use | Main risk |
|---|---|---|---|
| Centralized accounts | Each service’s database | The service | Breaches and many separate passwords |
| Federated identity | Identity provider | Identity provider and service | Tracking and dependence on the provider |
| Self-sovereign identity | Holder’s wallet | Only the verifier | Wallet loss and key management |
| Government wallet frameworks | Holder’s certified wallet | Verifier, under regulated rules | Governance and adoption challenges |
The European EUDI Wallet under eIDAS 2.0 adopts several SSI ideas, including holder-controlled wallets and selective disclosure, within a regulated framework of certified wallets and trusted issuers. Whether such systems count as fully self-sovereign is debated, because the state defines the rules and certifies the components.
Challenges and limitations
SSI shifts responsibility to the holder, and this creates practical difficulties that slow adoption. Most of them concern usability, governance and the gap between technical capability and real deployments.
- Key recovery: losing a device or keys can mean losing credentials unless a recovery method exists.
- Trust governance: verifiers still need rules about which issuers to trust.
- Over-asking verifiers: selective disclosure helps only if verifiers request minimal data.
- Fragmented standards: several credential formats and exchange protocols compete.
- Revocation privacy: checking whether a credential is revoked can leak usage if designed poorly.
A frequent misconception is that SSI requires a blockchain. Some early systems used distributed ledgers as registries, but many current deployments rely on conventional trust lists and web infrastructure instead.
Another misconception is that SSI removes the need for identity proofing. A credential is only as reliable as the checks the issuer performed before signing it, so strong enrollment, including document verification and liveness detection where appropriate, remains essential.
The simple explanation
Self-sovereign identity means that a person carries their own digital proofs of identity, such as a digital ID card or diploma, in an app on their phone. When a service needs proof, the person shows only what is required.
It resembles keeping your documents in your own wallet instead of in each shop’s filing cabinet. The difference is that the digital version can prove one fact, such as being an adult, without showing everything else on the card.
How it is used in practice
A university issues its graduates digitally signed diploma credentials that they store in a wallet app. A graduate applies for an engineering job abroad, and the employer’s hiring system requests proof of the degree and the field of study.
The graduate approves the request in the wallet, which presents only the degree title, field and issuing institution, not grades or the personal identification number. The employer’s system checks the university’s signature against a published trust list and confirms within seconds that the credential is valid and not revoked. The hiring process skips weeks of paper verification, and the university never learns where the diploma was shown.