Blockchain Security when Messages are Lost

TL;DR

This paper analyzes how message loss affects blockchain security, introducing a new model and deriving bounds on adversarial power that ensure protocol security even with unreliable communication.

Contribution

It introduces the $0- inite$ model for message loss and extends the security threshold analysis for proof-of-work protocols under these conditions.

Findings

Security violation probability decays almost exponentially with security parameter.

The new model captures message loss effects more realistically than previous models.

Extended the known regime of tolerable adversarial power in noisy communication settings.

Abstract

Security analyses for consensus protocols in blockchain research have primarily focused on the synchronous model, where point-to-point communication delays are upper bounded by a known finite constant. These models are unrealistic in noisy settings, where messages may be lost (i.e. incur infinite delay). In this work, we study the impact of message losses on the security of the proof-of-work longest-chain protocol. We introduce a new communication model to capture the impact of message loss called the $0-\infty$ model, and derive a region of tolerable adversarial power under which the consensus protocol is secure. The guarantees are derived as a simple bound for the probability that a transaction violates desired security properties. Specifically, we show that this violation probability decays almost exponentially in the security parameter. Our approach involves constructing combinatorial objects from blocktrees, and identifying random variables associated with them that are amenable to analysis. This approach improves existing bounds and extends the known regime for tolerable adversarial threshold in settings where messages may be lost.