Everything is a Race and Nakamoto Always Wins
This provides foundational security guarantees for blockchain consensus protocols, addressing a critical problem for developers and users by confirming attack limits.
The paper proves that the private double-spend attack is the worst-case attack for three longest chain protocols (Proof-of-Work, Proof-of-Stake, Proof-of-Space), leading to exact characterizations of maximum tolerable adversary power as a function of block time and network delay.
Nakamoto invented the longest chain protocol, and claimed its security by analyzing the private double-spend attack, a race between the adversary and the honest nodes to grow a longer chain. But is it the worst attack? We answer the question in the affirmative for three classes of longest chain protocols, designed for different consensus models: 1) Nakamoto's original Proof-of-Work protocol; 2) Ouroboros and SnowWhite Proof-of-Stake protocols; 3) Chia Proof-of-Space protocol. As a consequence, exact characterization of the maximum tolerable adversary power is obtained for each protocol as a function of the average block time normalized by the network delay. The security analysis of these protocols is performed in a unified manner by a novel method of reducing all attacks to a race between the adversary and the honest nodes.