3.1 List three approaches to message authentication.
3.2 What is a message authentication code?
3.4 What properties must a hash function have to be useful for message authentication?
3.5 In the context of a hash function, what is a compression function?
3.6 What are the principal ingredients of a public-key cryptosystem?
3.7 List and briefly define three uses of a public-key cryptosystem.
3.8 What is the difference between a private key and a secret key?
3.9 What is a digital signature?