Patrik Keller

Patrik Keller, Martin Florian, Rainer Böhme

Privacy-seeking cryptocurrency users rely on anonymization techniques like CoinJoin and ring transactions. By using such technologies benign users potentially provide anonymity to bad actors. We propose overlay protocols to resolve the tension between anonymity and accountability in a peer-to-peer manner. Cryptocurrencies can adopt this approach to enable prosecution of publicly recognized crimes. We illustrate how the protocols could apply to Monero rings and CoinJoin transactions in Bitcoin.

Patrik Keller, Rainer Böhme

A fundamental conflict of many proof-of-work systems is that they want to achieve inclusiveness and security at the same time. We analyze and resolve this conflict with a theory of proof-of-work quorums, which enables a new bridge between Byzantine and Nakamoto consensus. The theory yields stochastic uniqueness of quorums as a function of a security parameter. We employ the theory in HotPoW, a scalable permissionless distributed log protocol that supports finality based on the pipelined three-phase commit previously presented for HotStuff. We evaluate HotPoW and variants with adversarial modifications by simulation. Results show that the protocol can tolerate network latency, churn, and targeted attacks on consistency and liveness with a small storage overhead compared to plain Nakamoto consensus and less complexity than protocols that rely on sidechains for finality.