• A standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, the basis for HTTPS. They are also used in offline applications, like electronic signatures. An X.509 certificate contains a public key and an identity, and is either signed by a certificate authority or self-signed. X.509 is defined by the International Telecommunications Union’s Standardization Sector (ITU-T), and is based on ASN.1, another ITU-T standard. ← Wikipedia ↑ itu.int/rec/T-REC-X.509

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