An Analytical Study of Selfish Mining Attacks on Chainweb Blockchain

Chainweb and some other parallel blockchain systems have recently been proposed, with the objectives of improving the throughput and enhancing the tamper-proof capability. While many security related studies have been conducted for traditional single-chain based blockchain systems, the security aspect of parallel chain systems is yet to be well studied and understood. Our paper presents a systematic study on selfish mining attacks in Chainweb based on mathematical modeling. Specifically, selfish mining is conducted by concentrating the computation power on a subset of parallel chains and operating a proper withholding strategy. We demonstrate how to establish a Markov chain based analytical model with innovative techniques to handle the very large state space. Our Markov chain model is also capable of handling different number of parallel chains. The mathematical analysis brings an insightful, in fact counterintuitive, finding that the attackers need less computation power to harvest additional rewards through withholding when Chainweb contains a larger number of chains; while the common understanding is that the more chains are used, the more tamper-proof the system is. The accuracy of the Markov chain analysis is demonstrated via comparison to the simulation results.