1.5 Message Authentication Code

This is a historical learning note and may contain outdated or incomplete understanding.

1. What Is a Message Authentication Code

MAC, a technique used to verify message integrity and perform authentication.

2. Message Authentication Code Properties

Integrity + authentication.

3. Purpose of a Message Authentication Code

Ensure that data has not been tampered with – a hash function is used.
Authenticate the sender – only the two parties have the key.

4. Message Authentication Code Process

5. Problems with Message Authentication Codes

The key cannot be distributed effectively.
Third-party proof cannot be provided.
It cannot prevent the sender from denying having sent the message.

5.1. Solution

Digital signature.

6. How to Implement a Message Authentication Code

6.1. HMAC

A method of constructing a message authentication code using a hash function.

7. Advanced Message Authentication Codes

A message authentication code itself does not automatically prevent replay attacks; normally a nonce, timestamp, sequence number, or similar authenticated data is also required. How to design an open API interface