digital certificate 
A digital certificate is the equivalent of an ID card issued to an individual or an organization. Often taking the form of a password-protected file, a digital certificate may hold a variety of information, including the name and email address of the certificate holder, an encryption key that can be used to verify the digital signature of the holder, the name of the company issuing the certificate, and the period during which the certificate is valid. Digital certificates are issued by a trusted third party known as a certificate authority (CA). Most CAs create certificates in the X.509 file format, a widely accepted standard.