The Effect of Replica Placement on Routing Robustness in Distributed Hash Tables

To achieve higher efficiency over their unstructured counterparts, structured peer-to-peer systems hold each node responsible for serving a specified set of keys and correctly routing lookups. Unfortunately, malicious participants can abuse these responsibilities to deny access to a set of keys or misroute lookups. We look to address both of these problems through replica placement. Using Chord as an example, we present an equally-spaced replication scheme and prove that it can be tuned to produce any desired number of disjoint routes. To be specific, we prove that d disjoint routes can be produced by placing 2^d-1 replicas around a fully populated Chord ring in an equally-spaced fashion. In this situation, we also prove that there exists a route to at least one replica, which contains only uncompromised nodes, even if an attacker controls more than a quarter of the contiguous identifier space in the system. Simulation experiments demonstrate that this scheme performs better than previously proposed replica placement schemes in rings that are sparsely populated, populated in clusters, or populated partially by compromised nodes