Bitcoin Security under Temporary Dishonest Majority

TL;DR

This paper proves Bitcoin's security under conditions where the majority of online participants are honest on expectation, even with temporary offline participants and crash failures, across multiple network models.

Contribution

It extends Bitcoin security proofs to scenarios with temporary dishonest majority, including crash failures and message losses, across various network models.

Findings

Bitcoin remains secure under temporary dishonest majority in all models

Security is maintained with honest online majority on expectation

The analysis covers synchronous, bounded delay, and message loss models

Abstract

We prove Bitcoin is secure under temporary dishonest majority. We assume the adversary can corrupt a specific fraction of parties and also introduce crash failures, i.e., some honest participants are offline during the execution of the protocol. We demand a majority of honest online participants on expectation. We explore three different models and present the requirements for proving Bitcoin's security in all of them: we first examine a synchronous model, then extend to a bounded delay model and last we consider a synchronous model that allows message losses.