Bitcoin Is Broken

Specifically, in a paper we placed on arXiv, Ittay Eyal and I outline an attack by which a minority group of miners can obtain revenues in excess of their fair share, and grow in number until they reach a majority. When this point is reached, the Bitcoin value-proposition collapses: the currency comes under the control of a single entity; it is no longer decentralized; the controlling entity can determine who participates in mining and which transactions are committed, and can even roll back transactions at will. This snowball scenario does not require an ill-intentioned Bond-style villain to launch; it can take place as the collaborative result of people trying to earn a bit more money for their mining efforts.