  Consider a set of parties invited to execute a protocol $\Pi$. The protocol
will incur some cost to run while in the end (or at regular intervals), it will
populate and update local tables that assign (virtual) rewards to participants.
Each participant aspires to offset the costs of participation by these virtual
payoffs that are provided in the course of the protocol. In this setting, we
introduce and study a notion of coalition-safe equilibrium. In particular, we
consider a strategic coalition of participants that is centrally coordinated
and potentially deviates from $\Pi$ with the objective to increase its utility
with respect to the view of {\em at least one} of the other participants. The
protocol $\Pi$ is called a coalition-safe equilibrium with virtual payoffs
(EVP) if no such protocol deviation exists. We apply our notion to study
incentives in blockchain protocols. We proceed to use our framework to provide
a unified picture of incentives in the Bitcoin blockchain, for absolute and
relative rewards based utility functions, as well as prove novel results
regarding incentives of the Fruitchain blockchain protocol [PODC 2017] showing
that the equilibrium condition holds for collusions up to $n-1$ players for
absolute rewards based utility functions and less than $n/2$ for relative
rewards based utility functions, with the latter result holding for any "weakly
fair" blockchain protocol, a new property that we introduce and may be of
independent interest.
