X.509
termnetworking
The certificate format published by the ITU in 1988 and profiled for the internet in RFC 5280, binding a name to a public key with an issuer's signature.
It carries the subject, the public key, the validity dates, the issuer and the extensions that decide what the certificate may be used for, all signed by the issuing authority. It comes from the same standards programme as the X.500 directory, which is why its structures feel like a directory's and why so many operational problems are really encoding problems. Most certificate faults in practice are not cryptographic: a missing intermediate, a name that does not match, or dates nobody was watching.
Also known as: x.509, x509 certificate