CompTIA Security Plus Mock Test Q1131

Joe must send Ann a message and provide Ann with assurance that he was the actual sender. Which of the following will Joe need to use to BEST accomplish the objective?

A. A pre-shared private key
B. His private key
C. Ann’s public key
D. His public key

Correct Answer: B
Section: Cryptography

To achieve both authentication and confidentiality, Joe should include Ann’s name in the message, sign it using his private key, and then encrypt both the message and the signature
using Ann’s public key.

Incorrect Answers:
A: Because pre-shared keys are held by both parties to the communication, it can be compromised at one end, without the knowledge of anyone at the other.
C: Anybody encrypt the message using Anne’s public key, so this would not prove that Joe is the actual sender.
D: Joe would sign the message with his private key, not his public key.