Which of the following ensures a senders authenticity and an e-mails confidentiality?

A. Encrypting the hash of the message with the senders private key and thereafter encrypting the hash of the message with the receivers public key

B. The sender digitally signing the message and thereafter encrypting the hash of the message with the senders private key

C. Encrypting the hash of the message with the senders private key and thereafter encrypting the message with the receivers public key

D. Encrypting the message with the senders private key and encrypting the message hash with the receivers public key.

Explanation:

To ensure authenticity and confidentiality, a message must be encrypted twice: first with the senders private key, and then with the receivers public key. The receiver can decrypt the message, thus ensuring confidentiality of the message. Thereafter, the decrypted message can be decrypted with the public key of the sender, ensuring authenticity of the message. Encrypting the message with the senders private key enables anyone to decrypt it.