Public Key Authentication Service What is a public key certificate? A public key certificate is a web certificate that is used for ensuring the security of transactions handled over the web such as online purchases, etc. A digital signature made with a public key certificate enables the ability to identify the signatory, prevents forgery and/or illicit fabrication of electronic documents, and verifies transactions. Public key certificat! es are issued only by authentication institutes authorized by the government through a strict screening process, so legal force and safety are guaranteed.