Securely Boosting Chain Growth and Confirmation Speed in PoW Blockchains

Abstract

Proof-of-Work (PoW) blockchains add blocks, and consequently the chain weight, randomly. The blocks added also have a significant network delay owing to their large size. Large delay combined with randomness causes forks that are responsible for many security problems. One can reduce fork occurrences by designing a system with large block intervals and size but this design compromises performance aspects such as confirmation time guarantees. The trade-off between security and performance in PoW blockchain is a well discussed topic in the literature. In this paper, we aim to reduce the conflict between security and performance through our novel concept of Links. Links are small, fast and frequent structures that can be incorporated on any new or existing PoW blockchains. Links help reduce the confirmation time of its underlying blockchain while preserving its consistency security guarantees. Our novel lower-bound growth rate for PoW systems with links in the presence of a general adversary in a partially synchronous network, shows that links provide a more steady chain growth rate than classic PoW systems without links. On a well-established, secure system like Bitcoin, we use the derived growth rate to show that when links are incorporated to Bitcoin, they help reduce its confirmation time from 60 minutes by half to 30 minutes, while retaining the consistency threshold guarantees of the original Bitcoin system. We provide a proof of concept emulation of links in a Bitcoin test bed consisting of 210 nodes having real world latencies between them. We benchmark a system with links against Bitcoin to show links cause negligible network overheads and no compromises on security in terms of orphaned weight due to forks. Our theoretical analyses and experiments can easily be extended to other Nakamoto style PoW systems.