# What is a Digital Certificate?

> A digital certificate is a signed data structure that associates a public key with a named subject, identity, role, device, service, or other attributes under an issuer’s rules.

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## Content

In the X.509 model, it carries a serial number, issuer, validity interval, signature algorithm, and extensions that can constrain names, purposes, policies, and certification paths.

A relying party validates the issuer’s signature and a path to an accepted trust anchor, then applies the time, name, usage, constraint, policy, algorithm, and status checks required by the application.

### Key points

- **Binding and provenance:** The issuer signs the certificate after following its validation and approval process, allowing verifiers to detect changes and identify the authority responsible for the assertion.
- **Scope and constraints:** Extensions can identify valid names, permitted key uses, whether the subject may issue other certificates, relevant policies, and paths to issuer or status information.
- **Operational use:** Certificates support authenticated key establishment, digital signatures, device or workload identity, document signing, code signing, and other applications when the surrounding protocol validates them correctly.
- **Important limitation:** A valid certificate does not prove that its subject is honest, safe, uncompromised, or still controls the private key. It proves only that validation succeeded under particular trust anchors, policies, evidence, and time and status assumptions.

### Related terms

[Public key infrastructure (PKI)](<https://yellowcube.eu/glossary/public-key-infrastructure/>) · [Certificate management](<https://yellowcube.eu/glossary/certificate-management/>) · [Online Certificate Status Protocol (OCSP)](<https://yellowcube.eu/glossary/online-certificate-status-protocol/>) · [Authentication](<https://yellowcube.eu/glossary/authentication/>) · [Secure boot](<https://yellowcube.eu/glossary/secure-boot/>) · [Transport Layer Security (TLS)](<https://yellowcube.eu/glossary/transport-layer-security/>)

### Sources

[RFC 5280: Internet X.509 Public Key Infrastructure Certificate and CRL Profile](https://www.rfc-editor.org/info/rfc5280) · [ITU-T X.509: Public-Key and Attribute Certificate Frameworks](https://www.itu.int/rec/T-REC-X.509) · [RFC 3647: Certificate Policy and Certification Practices Framework](https://www.rfc-editor.org/info/rfc3647)

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