Which of the following encrypt/decrypt steps provides the GREATEST assurance of achieving confidentiality, message integrity and nonrepudiation by either sender or recipient? 
A、The recipient uses their private key to decrypt the secret key. 
B、The encrypted prehash code and the message are encrypted using a secret key. 
C、The encrypted prehash code is derived mathematically from the message to be sent. 
D、The recipient uses the sender's public key, verified with a certificate authority, to decrypt the prehash code.