  A major limitation of open P2P networks is the lack of strong identities.
This allows any agent to attack the system by creating multiple false personas,
thereby disrupting the overlay network's connectivity and sabotaging its
operation. In this paper, we explore practical ways to defend P2P networks from
such attacks. To do so, we employ a game theoretic approach to the management
of each peer's list of known nodes and to the overlay construction mechanisms
that utilize this list. We consider the interaction between defender and
attacker agents as a zero-sum game. We show that the cost of attacks can be
driven up substantially if the defender utilizes available information about
peers it chooses to connect to, such as their IP address. In addition to
theoretical analysis of the underlying game, we apply our approach to the
Bitcoin P2P network and derive effective strategies that guarantee a high
safety level against attacks.
