Privacy-Preserving Blockchain Mining: Sybil-resistance by Proof-of-Useful-Work

Blockchains rely on a consensus among participants to achieve decentralization and security. However, reaching consensus in an online, digital world where identities are not tied to physical users is a challenging problem. Proof-of-work (PoW) provides a solution by linking representation to a valuable, physical resource. This has worked well, currently securing Bitcoins $100 B value. However, the Bitcoin network uses a tremendous amount of specialized hardware and energy, and since the utility of these resources is strictly limited to blockchain security, the resources used are not useful other purposes. Here, we propose an alternative consensus scheme that directs the computational resources to a task with utility beyond blockchain security, aiming at better resource utilization. The key idea is to channel the resources to optimization of machine learning (ML) models by setting up decentralized ML competitions. This is achieved by a hybrid consensus scheme relying on three parties: data providers, miners, and a committee. The data provider makes data available and provides payment in return for the best model, miners compete about the payment and access to the committee by producing ML optimized models, and the committee controls the ML competition.