Theoretical analysis demonstrates secure proof-of-stake longest chain protocols against 50% adversaries with short-term predictability, indicating robust resilience against bribery attacks.
The Nakamoto longest chain protocol is remarkably simple and has been proven to provide security against any adversary with less than 50% of the total hashing power. Proof-of-stake (PoS) protocols are an energy efficient alternative; however existing protocols adopting Nakamoto's longest chain design achieve provable security only by allowing long-term predictability, subjecting the system to serious bribery attacks. In this paper, we prove that a natural longest chain PoS protocol with similar predictability as Nakamoto's PoW protocol can achieve security against any adversary with less than 1/(1+e) fraction of the total stake. Moreover we propose a new family of longest chain PoS protocols with a formal proof of their security against a 50% adversary, while only requiring short-term predictability.
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Bagaria et al. (2022) studied this question.
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