Suppose Bob wants to send a secret message to Alice, and Alice wants to be sure that the message was indeed sent by Bob. Then Bob should: (A) encrypt the message with Alice's public key, encrypt the result with his public key and then send the result. (B) encrypt the message with his public key, encrypt the result with Alice's public key, and send Alice the message. (C) encrypt the message with his private key, encrypt the result with Alice's private key, and then send the encrypted message to Alice. (D) encrypt the message with his private key, encrypt the result with Alice's public key, and then send the encrypted message to Alice.
