TwinsCoin: A Cryptocurrency via Proof-of-Work and Proof-of-Stake

We design and implement TwinsCoin, the €rst cryptocurrency based on a provably secure and scalable public blockchain design using both proof-of-work and proof-of-stake mechanisms. Di‚erent from the proof-ofwork based Bitcoin, our construction uses two types of resources, computing power and coins (i.e., stake). Œe blockchain in our system is more robust than that in a pure proof-of-work based system; even if the adversary controls the majority of mining power, we can still have the chance to secure the system by relying on honest stake. In contrast, Bitcoin blockchain will be insecure if the adversary controls more than 50% of mining power. Our design follows a recent provably secure proofof-work/proof-of-stake hybrid blockchain by Duong et al. (ePrint 2016). In order to make our construction practical, we enhance Duong et al.’s design. In particular, we introduce a new strategy for diculty adjustment in the hybrid blockchain and provide an analysis of it. We also show how to construct a light client for proof-of-stake cryptocurrencies and evaluate the proposal practically. We implement our new design. Our implementation uses a recent modular development framework for blockchains, called Scorex. It allows us to change only certain parts of an application leaving other codebase intact. In addition to the blockchain implementation, a testnet is deployed. Source code is publicly available. ∗IOHK. Email: [email protected]. †Virginia Commonwealth University. Email: duong‚[email protected]. ‡Shanghai Jiao Tong University. Partial work done while visiting the Cryptography Lab at Virginia Commonwealth University. Email: [email protected]. §Virginia Commonwealth University. Email: [email protected].