Well,
do you know the difference between a message authentication code and pure encryption?

AFAIcan remeber, for a MAC, Alice creates the mac, gives it together with the message to Bob, and bob can then compute the mac again(if he has the key) and compare the computation result to the transmitted code.
I think it was in that way.

and encryption of messages means to not even give the pain message to bob. alice encrypts it message , gives this "crap" to bob, and bob can decrypt it (again ifhe knows the key).

For encryption and decryption, youll need a cipher, see
http://delta.affinix.com/docs/qca/ci...p-example.html