certificates

Certificates are official documents or digital credentials that attest to a fact about a person, organization, or object. They serve as proof of identity, qualification, ownership, or authorization in various contexts.

Physical certificates are paper documents issued by authorities or institutions. Examples include birth certificates, marriage certificates, academic diplomas, professional licenses, and ownership certificates for property. They serve as official records used in identity verification, civil procedures, and administrative processes.

Digital certificates are electronic credentials that bind a public key to an identity. They are issued within a public key infrastructure (PKI) by trusted certificate authorities (CAs). A typical certificate, often in X.509 format, includes the subject’s identity, the issuer, a public key, a validity period, and a digital signature from the issuer. Recipients can verify authenticity through the issuer’s trusted chain.

Common types include SSL/TLS certificates for securing websites, code signing certificates for software integrity, client certificates for user authentication, and email certificates for S/MIME encryption. Self-signed certificates do not rely on a CA and are suitable for testing or internal networks; wildcard certificates cover multiple subdomains under a single domain.

Certificates require maintenance: they have expiration dates, must be renewed, and can be revoked if the private key is compromised or the information changes. Revocation lists (CRLs) and online certificate status protocols (OCSP) provide current validity information. Proper storage and backup, including hardware security modules for private keys, are important.

While digital certificates are essential to secure communications and authentication online, physical certificates remain important for official records and legal identification in many jurisdictions. Standards such as X.509 and practices within PKI underpin modern trust models.