Peer-to-peer networks have many advantageous security properties, including decentralization, natural load-balancing, and data replication. However, one disadvantage of decentralization is its exclusion of any central authority who can detect and evict malicious peers from the network. It is therefore relatively easy to sustain distributed denial-of-service attacks against these networks; malicious peers simply join the network and fail to forward messages. This article shows that peer-to-peer message-dropping attacks can be understood in terms of a well-established category of economic theory: the theory of the second best . In particular, peers who wish to continue service during an attack seek a second best solution to a utility optimization problem. This insight reveals useful connections between economic literature on the second best and computer science literature on peer-to-peer security. To illustrate, we derive and test an economics-inspired modification to the Chord peer-to-peer routing protocol that improves network reliability during message-dropping attacks. Under simulation, networks using the modified protocol achieve a 50% increase in message deliveries for certain realistic attack scenarios.
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