Event-Driven Private Counters
E. Goh and P. Golle.
We define and instantiate a cryptographic scheme called "private
counters", which can be used in applications such as preferential
voting to express and update preferences (or any secret) privately and
non-interactively. A private counter consists of an encrypted value
together with rules for updating that value if certain events
occur. Updates are private: the rules do not reveal how the value of
the counter is updated, nor even whether it is updated for a certain
event. Updates are non-interactive: a counter can be updated without
communicating with its creator. A private counter also contains an
encrypted bit indicating if the current value in the counter is within
a pre-specified range.
We also define a privacy model for private counters and prove that our
construction satisfies this notion of privacy. As an application of
our private counters, we present efficient protocols for preferential
voting and auctions. Our solution for preferential voting hides the
order in which voters rank candidates, and thus offers greater privacy
guarantees than any other preferential voting scheme.