  In this expository paper we discuss a relatively new counterfeit coin problem
with an unusual goal: maintaining the privacy of, rather than revealing,
counterfeit coins in a set of both fake and real coins. We introduce two
classes of solutions to this problem --- one that respects the privacy of all
the coins and one that respects the privacy of only the fake coins --- and give
several results regarding each. We describe and generalize 6 unique strategies
that fall into these two categories. Furthermore, we explain conditions for the
existence of a solution, as well as showing proof of a solution's optimality in
select cases. In order to quantify exactly how much information is revealed by
a given solution, we also define the revealing factor and revealing
coefficient; these two values additionally act as a means of comparing the
relative effectiveness of different solutions. Most importantly, by introducing
an array of new concepts, we lay the foundation for future analysis of this
very interesting problem, as well as many other problems related to privacy and
the transfer of information.
