What protection do message-by-message cryptographic systems provide?

• A. Message Authentication
• B. Message Integrity
• C. Message Confidentiality
• D. All of the Above

Answer: (D)

Protecting each message often combines encryption with a mechanism to verify integrity and identity. Encrypting the message ensures only the intended recipient can read it, giving confidentiality. A MAC or digital signature attached to the message provides integrity by letting the recipient detect any tampering, and it also authenticates the sender by proving who created the message (either through a shared key in a MAC or through a digital signature with a public key). When you apply both encryption and an integrity/authentication mechanism to every message, you achieve all three protections: confidentiality, integrity, and authentication. That’s why all of the above is the best answer.