Digital signature users register their public keys with a certification authority, which distributes a certificate containing the user's public key and digital signature of the certification authority. In create the certificate, the user's public key and the validity period are combined with what other information before computing the digital signature?

A. Certificate issuer and the Digital Signature Algorithm identifier 
B. User's private key and the identifier of the master key code 
C. Name of secure channel and the identifier of the protocol type 
D. Key authorization and identifier of key distribution center