X.509 Digital Certificate

Abstract

An X.509 certificate is a very important type of digital document used in many cryptographic systems. A bare public key is not very secure. A malicious actor could trick you into using a bogus public key (for which they have the corresponding private key). A digital certificate wraps a public key in a document that includes information about the key (length, algorithm) and the identity of the person or object that the digital certificate belongs to. It binds a public key to a person’s or object’s identity. Anyone can verify the validity of a digital certificate, which provides trust. Like a credit card, an X.509 certificate has an expiration date. You should not accept an expired certificate unless you know what you are doing (e.g. reading an old encrypted e-mail).