X.509 certificate

Certificate Files supply the public key of somebody you wish to communicate with securely, such as a client or vendor. They are used in electronic transaction processing, for instance. You may need to install a vendor's certificate file on your system in order to send transactions such as credit card sales to be processed.

Samples, references, and external links

 * Public-key cryptography (Wikipedia)
 * Info and downloadable certificate file at Cybersource site