Greedy-Mine: A Profitable Mining Attack Strategy in Bitcoin-NG

Bitcoin-NG is an extensible blockchain protocol based on the same trust model as Bitcoin. It divides each epoch into one keyblock and multiple microblocks, effectively improving the transaction processing capacity. Bitcoin-NG adopts a special incentive mechanism (i.e., the transaction fees in each epoch are split to the current and next leader) to maintain its security. However, there are some limitations to the existing incentive analysis of Bitcoin-NG in recent works. First, the incentive division method of Bitcoin-NG only includes some specific mining attack strategies of the adversary, while ignoring more stubborn attack strategies. Second, once adversaries find a whale transaction, they will deviate from the honest mining strategies to obtain an extra reward. In this paper, we are committed to solving these two limitations. First, we propose a novel mining strategy named Greedy-Mine attack. Then, we formulate a Markov reward process (MRP) model to analyze the competition of honest miners and adversaries. Furthermore, we analyze the extra reward of adversaries and summarize the mining power proportion required for malicious adversaries to launch Greedy-Mine to obtain extra returns. Meanwhile, we make a backward-compatibility progressive modification to Bitcoin-NG protocol that would raise the threshold of propagation factor from 0 to 1. Finally, we get the winning condition of adversaries when adopting Greedy-Mine, compared with honest mining. Simulation and experimental results indicate that Bitcoin-NG is not incentive compatible, which is vulnerable to Greedy-Mine attack.