How does Hmac provide authentication?

Related questions

1. How is an HMAC different than a hash?
2. What is SHA HMAC?
3. How does an HMAC work?
4. How good is AES 256 encryption?
5. How does a message authentication code work?
6. What is the difference between a message authentication code and a one way hash function?
7. What is Entity Authentication?
8. Is sha1 secure?
9. What are the message authentication functions?
10. What is the most secure hashing algorithm?

Tags

1. #function
2. #mechanism
3. #authentication
4. #calculating
5. #authenticity
6. #combination
7. #message
8. #secret
9. #involving
10. #based
11. #integrity
12. #verify