ZCC: Mitigating Double-spending Attacks in Micropayment Bitcoin Transactions

Bitcoin is one of the popular cryptocurrencies but it has many pitfalls due to its slow payment nature. The average confirmation time of a Bitcoin transaction is ten minutes. Block propagation, validation, and mining are time-consuming tasks in the Bitcoin network. They increase confirmation delay, which becomes a large overhead, especially for micropayment transactions. In a micropayment transaction, the buyer expects quick service and the seller expects fast payment. Another downside of excess delay is that attackers get better chances to perform successful double-spending attacks. In this paper, we propose a protocol named ZCC that not only provides quick service to users but also guarantees payment to sellers. In ZCC, a group of full nodes acts as an approval committee that commits the user's ZCC transactions based on majority approvals obtained from group members. In the ZCC scheme, mining time is much less compared to the mining time of Bitcoin transactions because of lower difficulty targets. We analyze total acceptance time and the probability of a double-spending attack in the ZCC scheme. Also, we evaluate the performance of ZCC using the BlockSim simulator for the different transaction and block-related parameters, and observe substantially improved performance for the ZCC scheme.