Chris Dowden
Agreement Protocols in the Presence of a Mobile Adversary

Suppose various processors in a network wish to reach agreement on a
particular decision. Unfortunately, some unknown subset of these may be
under the control of a malicious adversary who desires to prevent such an
agreement being possible. 
 
To this end, the adversary will instruct his "faulty" processors to provide
inaccurate information to the non-faulty processors in an attempt to mislead
them. The aim is to construct an "agreement protocol" that will always foil
the adversary and enable the non-faulty processors to reach agreement
successfully (perhaps after several rounds of communication).
 
In traditional agreement problems, it is usually assumed that the set of
faulty processors is "static", in the sense that it is chosen by the
adversary at the start of the process and then remains fixed throughout all
communication rounds. In this talk, we shall instead focus on a "mobile"
version of the problem, providing results both for the case when the
communications network forms a complete graph and also for the general case
when the network is not complete.