Enhancing Bitcoin Security and Performance with Strong Consistency via Collective Signing

While showing great promise, Bitcoin requires users to wait tens of minutes transactions to commit, and even then, offering only probabilistic. This paper introduces ByzCoin, a novel Byzantine consensus protocol leverages scalable collective signing to commit Bitcoin transactions within seconds. ByzCoin achieves Byzantine consensus while Bitcoin's open membership by dynamically forming hash-proportionate consensus groups that represent recently-successful block. ByzCoin employs communication trees to optimize transaction commitment verification under normal operation while guaranteeing safety and liveness Byzantine faults, up to a near-optimal tolerance of f faulty group among 3f + 2 total. ByzCoin mitigates double spending and selfish attacks by producing collectively signed transaction blocks within one of transaction submission. Tree-structured communication further reduces latency to less than 30 seconds. Due to these optimizations, ByzCoin a throughput higher than PayPal currently handles, with a confirmation of 15-20 seconds.