I understand the difference between MAC (eg. hmac_sha256, etc.) and Symmetrical Encryption (eg. rc4, etc.), but my question is what advantage does MAC solve that using encryption doesn't?
I know that MAC is used to verify that the message is both from the intended source, and did not get tampered though transmission by hashing the message with a secret key.
If you encrypt the message with rc4 (or any other algorithm, strength beside the point), then does this not accomplish the same result, the receiver would still need to know the secret key to decrypt the message.
The only difference I can think of is with MAC the message itself is plain text, so the authentication of the message is very fast. So is performance the only difference? Or is it the fact that the message contents are not confidential and you only want to validate whether it's genuine or not.
Any information on these two concepts would be greatly appreciated.