certificate

A certificate is a document that attests to a fact or achievement. It can be a formal written attestation issued by an organization to certify a person’s identity, status, or completion of a program, or a digital credential used in information technology.

Physical certificates typically include the recipient’s name, the credential, the issuing authority, dates, and signatures or seals to deter forgery. Common examples include birth certificates, diplomas, professional licenses, and honorary certificates.

Digital certificates use public key cryptography to bind a public key to an identity. They follow standards such as X.509 and are issued by trusted certificate authorities. A certificate lists the subject, issuer, validity period, the subject’s public key, and a digital signature. They enable authentication, encryption, and data integrity, and are widely used for TLS/SSL, code signing, email, and client authentication.

Management is part of a public key infrastructure. CAs verify identity to varying levels (domain, organization, or extended validation). Certificates expire and may be renewed; compromised or invalid certificates can be revoked, with certificate revocation lists and online status protocols used to check status. Certificate transparency helps detect mis-issuance.

Beyond IT, a certificate can be a credential for completing a training, course, or examination, or a professional license. In professional contexts, certification refers to a credential earned from a certifying body after meeting requirements, and is distinct from a certificate documenting completion of a course.

Related concepts include certificate authority, PKI, and X.509.