🚀 go-pugleaf

In article <C13L7D.1M7@dcs.ed.ac.uk> pdc@dcs.ed.ac.uk (Paul Crowley) writes:
> At the moment, I can't think how to define the problem precisely enough
> to prove that spoofing is impossible.

Assume there is an automorphism of the universe which switches Bob and
Charlie. Then no matter what Alice does, she can't tell the difference
between Bob and Charlie. More precisely, Alice cannot define the
function which is 1 for Bob and 0 for Charlie, because this function
is not invariant under the automorphism.

In practice, for this automorphism to exist, Bob and Charlie have to
start with all the same information, receive all the same information,
and be in a position to send all the same information.

---Dan