Analyzing the Fundamental Liveness Property of the Chord Protocol

Chord is a protocol that provides a scalable distributed hash table over an underlying peer-to-peer network. Since it combines data structures, asynchronous communications, concurrency, and fault tolerance, it features rich structural and temporal properties that make it an interesting target for formal specification and verification. Previous work has mainly focused on automatic proofs of safety properties or manual proofs of the full correctness of the protocol (a liveness property). In this paper, we report on analyzing automatically the correctness of Chord with the Electrum language (developed in former work) on small instance of networks. In particular, we were able to find various corner cases in previous work and showed that the protocol was not correct as described there. We fixed all these issues and provided a version of protocol for which we were not able to find any counterexample using our method.