Securely Improving Stability and Performance of PoW Blockchains Using Anchors

Proof-of-work (PoW) consensus generates blocks at random time instants, and consequently, adds weight to the blockchain at these random instants. This unsteady increase in chain weight over time along with the large network delay of blocks is the root cause of many security and performance problems such as high fork resolution times, vulnerability to double-spend and selfish mining attacks, and also a high block confirmation time. In this paper, we propose a novel signaling scheme of PoW called Anchors that can be implemented on any PoW blockchain system to improve their stability, reduce fork resolution times, prevent forks, strengthen the system against double spend attacks and reduce block confirmation times by half. In a partially synchronous model with a general adversary, we prove that a system with anchors has faster, more stable chain growth as compared to PoW systems without anchors and show that consistency security bounds established by prior work are preserved as in the underlying blockchain. We incorporate anchors in a reference Bitcoin implementation and perform experiments to support our claims in a 210 node test-bed with real world latencies. Our results show that anchors propagate at least 6 times faster than blocks, help resolve forks much faster than Bitcoin (without anchors) does and are able to even prevent forks from occurring.