Add machine-to-machine coverage

[dbosk]

This would be details on crypto protocols for authentication. Basically, we can reduce much of user-machine and machine-user to machine-machine due to the user using e.g. a smartphone.

[dbosk]

This should include #21: Add authenticated-key exchange and authenticated key-exchange.

[dbosk]

From #6: Machine-to-machine might also be covered by keyauth.