A step beyond "Eyeballing" a protocol.
Attacks on authentication protocols use one of several flaws in the protocol:
Logics for protocol analysis are traditionally split into two groups, epistemic logics, where everything is based on knowledge (if any party believes X, X is true, i.e. all statements are of absolute fact) and doxastic logics wher everything is based on belief. It can be shown to that these two logics are equivalent but it is traditional and more natural to use doxastic logics when reasoning about trust and epistemic logics when reasoning about security.