选择题 .  Certificates are ______ documents attesting to the ______ of a public key to an individual or other entity. They allow verification of the claim that a given public key does in fact belong to a given individual. Certificates help prevent someone from using a phony key to ______ someone else. In their simplest form, certificates contain a public key and a name. As commonly used, a certificate also contains an ______ date, the name of the CA that issued the certificate, a serial number, and perhaps other information. Most importantly, it contains the digital ______ of the certificate issuer. The most widely accepted format for certificates is X.509, thus, certificates can be read or written by any application complying with X.509.71.