Public key infrastructure

Public key infrastructure (PKI) is a system of policies, certificate authorities, and digital certificates that binds public keys to identities and supports trust in cryptographic communications.

X.509: A standard format for public key certificates and related identity information. PKI commonly uses X.509 certificates to encode identities, public keys, and issuer signatures.
Public-key cryptography: Cryptography using mathematically related public and private keys for encryption, signatures, or key agreement. PKI organizes public keys and identities; it does not replace the cryptographic operations those keys enable.
Transport Layer Security: A protocol that protects network connections through encryption, authentication, and integrity checks. TLS uses certificates to authenticate servers and sometimes clients.
Web of trust: A decentralized model in which users certify one another's public keys and build trust through relationships. Unlike hierarchical PKI, it does not depend on a central certificate authority hierarchy.
Certificate authority: An entity that issues and digitally signs certificates binding public keys to identities. Certificate authorities create the signed credentials at the center of most PKI systems.
Digital signature: A cryptographic value that lets others verify a message's origin and integrity using a public key. Certificate issuers sign certificates so verifiers can detect changes and authenticate the issuer.
HTTPS: The use of HTTP over TLS to protect web communication and authenticate web servers. Web browsers rely on PKI to validate the certificates presented by HTTPS sites.
DANE: A protocol that uses DNSSEC-protected DNS records to associate services with TLS certificates or keys. DANE can publish certificate information through DNS instead of relying solely on public certificate authorities.
Certificate signing request: A message containing a public key and identifying information, signed by the holder of its corresponding private key. Applicants submit this request to obtain a certificate from a certificate authority.
Cryptographic hash function: A function that maps data to a fixed-length digest designed to resist collisions and reversal. Digital signatures commonly use hashes to represent certificate contents efficiently.

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