Bitcoin's Latency--Security Analysis Made Simple

TL;DR

This paper provides simple, exponential bounds on Bitcoin's Nakamoto consensus security, considering network delays and adversarial power, showing the safety probability for common confirmation rules.

Contribution

It introduces closed-form bounds for Bitcoin security that are easy to compute and apply regardless of attack strategies, with small gaps between bounds for real parameters.

Findings

6-block confirmation safety violation between 0.11% and 0.35%

Bounds are exponential in confirmation depth

Bounds are tight for Bitcoin parameters

Abstract

Simple closed-form upper and lower bounds are developed for the security of the Nakamoto consensus as a function of the confirmation depth, the honest and adversarial block mining rates, and an upper bound on the block propagation delay. The bounds are exponential in the confirmation depth and apply regardless of the adversary's attack strategy. The gap between the upper and lower bounds is small for Bitcoin's parameters. For example, assuming an average block interval of 10 minutes, a network delay bound of ten seconds, and 10% adversarial mining power, the widely used 6-block confirmation rule yields a safety violation between 0.11% and 0.35% probability.