Paper 2017/573

Ouroboros Praos: An adaptively-secure, semi-synchronous proof-of-stake protocol

Bernardo David
Peter Gaži
Aggelos Kiayias
Alexander Russell

We present ``Ouroboros Praos'', a proof-of-stake blockchain protocol that, for the first time, provides security against fully-adaptive corruption in the semi-synchronous setting: Specifically, the adversary can corrupt any participant of a dynamically evolving population of stakeholders at any moment so long as the stakeholder distribution maintains an honest majority of stake; furthermore, the protocol tolerates an adversarially-controlled message delivery delay unknown to protocol participants. To achieve these guarantees we formalize and realize in the universal composition setting a suitable form of forward secure digital signatures and a new type of verifiable random function that maintains unpredictability under malicious key generation. Our security proof develops a general combinatorial framework for the analysis of semi-synchronous blockchains that may be of independent interest. We prove our protocol secure under standard cryptographic assumptions in the random oracle model.

Available format(s)
Cryptographic protocols
Publication info
A minor revision of an IACR publication in EUROCRYPT 2018
blockchainconsensusproof of stake.
Contact author(s)
peter gazi @ iohk io
2023-04-27: last of 3 revisions
2017-06-14: received
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Creative Commons Attribution


      author = {Bernardo David and Peter Gaži and Aggelos Kiayias and Alexander Russell},
      title = {Ouroboros Praos: An adaptively-secure, semi-synchronous proof-of-stake protocol},
      howpublished = {Cryptology ePrint Archive, Paper 2017/573},
      year = {2017},
      note = {\url{}},
      url = {}
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