Cryptology ePrint Archive: Report 2020/917

Formalizing Nakamoto-Style Proof of Stake

Søren Eller Thomsen and Bas Spitters

Abstract: Fault-tolerant distributed systems move the trust in a single party to a majority of parties participating in the protocol. This makes blockchain based crypto-currencies possible: they allow parties to agree on a total order of transactions without a trusted third party. To trust a distributed system, the security of the protocol and the correctness of the implementation must be indisputable.

We present the first machine checked proof that guarantees both safety and liveness for a consensus algorithm. We verify a Proof of Stake (PoS) Nakamoto-style blockchain (NSB) protocol, using the foundational proof assistant Coq. In particular, we consider a PoS NSB in a synchronous network with a static set of corrupted parties. We define execution semantics for this setting and prove chain growth, chain quality, and common prefix which together implies both safety and liveness.

Category / Keywords: blockchain, formal methods

Date: received 23 Jul 2020

Contact author: sethomsen at cs au dk,spitters@cs au dk

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Version: 20200726:062248 (All versions of this report)

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