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A major limitation of many blockchain systems is the lack of strong identities in the underlying P2P network. This allows any nodes to attack the system by creating multiple false personas, thereby disrupting the network's connectivity and sabotaging its operation. In this paper, we focus on P2P networks, and explore practical ways to defend them 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 the defender and attacker as a 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 and practical …