True or False: A MAC is created by using a secret key and is added to a message for authentication.

• A. True
• B. False
• C. Conditional
• D. Dependent

Answer: (A)

A Message Authentication Code (MAC) is indeed created using a secret key, which adds a layer of authentication to messages. The primary purpose of a MAC is to ensure that both the authenticity and integrity of the message are maintained. This is accomplished by combining the message content with a secret key through a cryptographic function.

When the receiver receives the message along with the MAC, they can use the same secret key to generate their own MAC for the message. If the MAC they generate matches the one that was sent, it confirms that the message has not been altered and that it was indeed sent by someone who possesses the secret key. This mechanism is crucial in securing communications and preventing unauthorized alterations.

In contrast, a response indicating "False" would misunderstand the core functionality of MACs, which is fundamentally dependent on the use of a secret key for ensuring message authentication.