An ITU-T Recommendation (1988) for a public key infrastructure (PKI). X.509 establishes a hierarchical structure of certificate authorities (CAs) that issue digital certificates, which are electronic credentials that authenticate the identity of users on the Internet and intranets. See also authentication, CA, digital certificate, Internet, intranet, and PKI.
A public key certificate standard developed as part of the X.500 directory specification. It is used for the secure management and the distribution of digitally signed certificates across secure Internet networks.