A Combined Micro-block Chain Truncation Attack on Bitcoin-NG

Bitcoin-NG, introduced by Eyal et al. in NSDI 2016, divides a blockchain into key-blocks and micro-blocks to improve transaction process efficiency. In this paper, we propose a novel attack on Bitcoin-NG, called a micro-block chain truncation attack. Combined with key-block selfish and stubborn mining, and an eclipse attack, this attack is able to bring extra reward to attackers in Bitcoin-NG than in Bitcoin through a colluded strategy or a “destroyed if no stake” strategy. Our evaluation calculates the reward proportion of an attacker by these attacks on both Bitcoin-NG and Bitcoin, which helps us figure out whether Bitcoin-NG sacrifices security for efficiency promotion. We also evaluate 18 strategy combinations by traversing different values of computation power and practical truncation rate. In a setting with reasonable parameters, the optimal combined micro-block chain truncation attack obtains at most 5.28% more reward proportion in Bitcoin-NG than in Bitcoin.