To ensure authentication, confidentiality and integrity of a message, the sender should encrypt the hash of the message with the sender's: 
A、public key and then encrypt the message with the receiver's private key. 
B、private key and then encrypt the message with the receiver's public key. 
C、public key and then encrypt the message with the receiver's public key. 
D、private key and then encrypt the message with the receiver's private key.