Defending Blockchain Forking Attack by Delaying MTC Confirmation

Abstract

In terms of security, blockchain technology faces the potential risks of enormous attacks, among which forking attack is the most common one. Because of the decentralized structure of a blockchain, the trust degree directly relies on the length of the blockchain, which makes the longest chain on the current network the most trusted chain (MTC). The forking attack is the kind of hazard behavior that aims to replace the MTC by launching an alternative chain to gain benefits. Blockchain plays a vital role in multiple applications, such as cryptocurrency, and hence such forking attack leads to huge financial loss if it succeeds. In this paper, we propose a novel MTC confirmation mechanism to defend the forking attack. First, we theoretically analyze the success probability distribution of the forking attack and propose an estimation model of the attack's expected profit. Then, we propose an arbitration mechanism to enforce branches from a fork to have competition. With the arbitration mechanism, we delay the confirmation of the MTC until the end of the competition. We set up an end threshold as the termination condition of the competition process to help the MTC become the winner. Finally, we define two dynamic difficulty factors and apply them for changing the difficulty of mining to reduce the value of the end threshold, which can improve the performance of the mechanism. The experiments demonstrate our proposed MTC confirmation mechanism can enhance the blockchain security by enforcing the expected profit of an attack to be negative. In the meantime, the mechanism balances well in both effectiveness and efficiency.