Rigorous and Generalized Proof of Security of Bitcoin Protocol with Bounded Network Delay
For blockchain researchers, this work corrects a flaw in prior security proofs and strengthens the theoretical foundation of Bitcoin's liveness property.
The paper provides a rigorous proof of Bitcoin's security under bounded network delay, showing that honest blocks occur infinitely often if the honest mining rate exceeds the adversary's rate, preventing permanent censorship.
A proof of the security of the Bitcoin protocol is made rigorous, and simplified in certain parts. A computational model in which an adversary can delay transmission of blocks by time $Δ$ is considered. The protocol is generalized to allow blocks of different scores and a proof within this more general model is presented. An approach used in a previous paper that used random walk theory is shown through a counterexample to be incorrect; an approach involving a punctured block arrival process is shown to remedy this error. Thus, it is proven that with probability one, the Bitcoin protocol will have infinitely many honest blocks so long as the fully-delayed honest mining rate exceeds the adversary mining rate. This means that an adversary cannot censor future transactions of a user in perpetuity, which would render the protocol useless.