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2018 | OriginalPaper | Buchkapitel

Ouroboros Praos: An Adaptively-Secure, Semi-synchronous Proof-of-Stake Blockchain

verfasst von : Bernardo David, Peter Gaži, Aggelos Kiayias, Alexander Russell

Erschienen in: Advances in Cryptology – EUROCRYPT 2018

Verlag: Springer International Publishing

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Abstract

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 as long 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.

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Vorheriges Kapitel But Why Does It Work? A Rational Protocol Design Treatment of Bitcoin

Nächstes Kapitel Sustained Space Complexity

It is worth pointing out that the notion of slots we use in this work can be substantially shorter in terms of real time elapsed compared to the slots of [16], where each slot represented a full round of interaction between all participants.

Refer e.g., to the posts by QuantumMechanic and others from 2011 https://bitcointalk.org/index.php?topic=27787.0 (Last Accessed 19/09/2017).

We assume this to simplify our formal treatment, a variant of our protocol can actually accommodate “lazy honesty” as introduced in [19]. In this variant, honest stakeholders only come online at the beginning of each epoch and at a few infrequent, predictable moments, see the full version.

In fact our UC formulation captures a stronger notion: even for adversarial keys the VRF function will act as a random oracle. We note that while we can achieve this notion in the random oracle model, a weaker condition of mere unpredictability can be sufficient for the security of our protocol. A UC version of the notion of verifiable pseudorandom permutations, cf. [9], could potentially be used towards a standard model instantiation of the primitive.

Note that we utilize the q-bounded model only to provide a more refined analysis; given that the total length of the execution is polynomial in \(\lambda \) one may also use the total execution length as a bound.

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Titel: Ouroboros Praos: An Adaptively-Secure, Semi-synchronous Proof-of-Stake Blockchain
verfasst von: Bernardo David
Peter Gaži
Aggelos Kiayias
Alexander Russell
Verlag: Springer International Publishing
Buch: Advances in Cryptology – EUROCRYPT 2018
Print ISBN: 978-3-319-78374-1

Electronic ISBN: 978-3-319-78375-8

Copyright-Jahr: 2018
DOI: https://doi.org/10.1007/978-3-319-78375-8_3

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