Red Belly Blockchain was discovered three years ago and results from more than fifteen years of expertise in the field of distributed systems developed in research institutes among the best in the USA, France, Switzerland and Australia.
In this paper, we present the largest experiment of a blockchain system to date. To achieve scalability across 1000 servers in more than 10 countries located on four different continents, we drastically revisited Byzantine fault tolerant blockchains and verification of signatures. The resulting blockchain, called the Red Belly Blockchain (RBBC), commits more than a hundred thousand transactions issued by permissionless nodes, that are grouped into blocks within few seconds through a partially synchronous consensus run by permissioned nodes. It prevents double spending by guaranteeing that a unique block is decided at any given index of the chain in a deterministic way.
In this paper, we introduce Polygraph, the first accountable Byzantine consensus algorithm for partially synchronous systems. If among n users t<n/3 are malicious then it ensures consensus, otherwise it eventually detects malicious users that cause disagreement. Polygraph is appealing for blockchain applications as it allows them, if t<n/3, to totally order blocks in a chain, hence avoiding forks and double spending and, otherwise, to punish malicious users when a fork occurs.
We first show that stronger forms of the problem including a fixed time detection are impossible to solve before proving our solution. We also show that Polygraph has a bounded justification size so that each of its asynchronous rounds exchanges only O(n^2) messages. Finally, we use a blockchain application to evaluate Polygraph on a geodistributed system of 80 machines and show that accountability reduces the performance of the non-accountable baseline by about a third, still committing thousands of transactions per second.
As an alternative to the energy greedy proof-of-work, new blockchains constrain the set of participants whose selection is debatable. These blockchains typically allow a fixed consortium of machines to decide upon new transaction blocks. In this paper, we introduce the community blockchain that bridges the gap between these public blockchains and constrained blockchains. The idea is to allow potentially all participants to decide upon “some” block while restricting the set of participants deciding upon “one” block. We also propose an implementation called ComChain that builds upon the Red Belly Blockchain, the fastest blockchain we are aware of. It runs a consensus among the existing community to elect a new community. This reconfiguration speeds up as the number of removed nodes increases.