A digital certificate, also known as a public-key certificate, is a digital document that binds a public key to an entity. The certificate gives the end-user confidence that the public key contained in the certificate belongs to the end entity. This way, that entity (company, person, organization) can sign documents, programs, emails and other electronic files. The recipient can then check their copy of the file against the public key to verify that the file originated with that entity.

The most common structure and syntax of a certificate is contained in the International Telecommunications Union's ITU-T Recommendation X.509. This specification contains information about the user, certificate authority or issuer, serial number, validity period, issuer name & signature and a subject name. By viewing a certificate, you can view where the file came from. Certificates are not foolproof, but they can increase confidence that the file is an original, and has not been tampered with.

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