Protecting the confidentiality of a message is accomplished by encrypting the message with which of the
following?

A.
Sender’s private key

B.
Recipient’s public key

C.
Sender’s public key

D.
Recipient’s private key

Explanation:
To achieve both authentication and confidentiality, the sender should include the recipient’s name in the
message, sign it using his private key, and then encrypt both the message and the signature using the
recipient’s public key.
Incorrect Answers:
A: The sender’s private key is used to generate a digital signature, which is used for authentication.
C: The ender’s public key is not used for encrypting the message.
D: The recipient’s private key is used to decrypt the message.

https://en.wikipedia.org/wiki/Public-key_cryptography