Glossary:X.509
X.509 is a standard defining a format for a digital certificate, associating an identity such as the owner of a web site or email address or a software publisher and a public key. The certificate can then be used to cryptographically verify the authenticity of a web page, email or software purporting to come from the identity. The authenticity of the digital certificate itself is guaranteed by a chain of higher level digital certificates ending in a "root certificate" which everyone trusts.