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Erschienen in:
Stronger Security for Reusable Garbled Circuits, General Definitions and Attacks Kapitel lesen Erstes Kapitel lesen

2017 | OriginalPaper | Buchkapitel

The Bitcoin Backbone Protocol with Chains of Variable Difficulty

verfasst von : Juan Garay, Aggelos Kiayias, Nikos Leonardos

Erschienen in: Advances in Cryptology – CRYPTO 2017

Verlag: Springer International Publishing

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Abstract

Bitcoin’s innovative and distributedly maintained blockchain data structure hinges on the adequate degree of difficulty of so-called “proofs of work,” which miners have to produce in order for transactions to be inserted. Importantly, these proofs of work have to be hard enough so that miners have an opportunity to unify their views in the presence of an adversary who interferes but has bounded computational power, but easy enough to be solvable regularly and enable the miners to make progress. As such, as the miners’ population evolves over time, so should the difficulty of these proofs. Bitcoin provides this adjustment mechanism, with empirical evidence of a constant block generation rate against such population changes.
In this paper we provide the first formal analysis of Bitcoin’s target (re)calculation function in the cryptographic setting, i.e., against all possible adversaries aiming to subvert the protocol’s properties. We extend the q-bounded synchronous model of the Bitcoin backbone protocol [Eurocrypt 2015], which posed the basic properties of Bitcoin’s underlying blockchain data structure and shows how a robust public transaction ledger can be built on top of them, to environments that may introduce or suspend parties in each round.
We provide a set of necessary conditions with respect to the way the population evolves under which the “Bitcoin backbone with chains of variable difficulty” provides a robust transaction ledger in the presence of an actively malicious adversary controlling a fraction of the miners strictly below \(50\%\) at each instant of the execution. Our work introduces new analysis techniques and tools to the area of blockchain systems that may prove useful in analyzing other blockchain protocols.

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Vorheriges Kapitel Encryption Switching Protocols Revisited: Switching Modulo p
Nächstes Kapitel Bitcoin as a Transaction Ledger: A Composable Treatment
Anhänge
Nur mit Berechtigung zugänglich
Fußnoten
1
In Bitcoin, solving a proof of work essentially amounts to brute-forcing a hash inequality based on SHA-256.
 
2
In Bitcoin, m is set to 2016 and roughly corresponds to 2 weeks in real time—assuming the number of parties does not change much.
 
3
In the latest version of [10], we show that in the case of fixed difficulty, the analysis of the Bitcoin backbone in the synchronous model extends with relative ease to partial synchrony. We leave the extension of the variable-difficulty case for future work.
 
4
In [11] this is referred to as the “flat-model” in terms of computational power, where all parties are assumed equal. In practice, different parties may have different “hashing power”; note that this does not sacrifice generality since one can imagine that real parties are simply clusters of some arbitrary number of flat-model parties.
 
5
Note that in order to calculate f, we can consider that a round of full interaction lasts 18 s; If this is combined with the fact that the target is set for a POW to be discovered approximately every 10 min, we have that 18/600 = 0.3 is a good estimate for f.
 
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Metadaten
Titel
The Bitcoin Backbone Protocol with Chains of Variable Difficulty
verfasst von
Juan Garay
Aggelos Kiayias
Nikos Leonardos
Copyright-Jahr
2017
Buch
Advances in Cryptology – CRYPTO 2017

Print ISBN: 978-3-319-63687-0

Electronic ISBN: 978-3-319-63688-7

Copyright-Jahr: 2017

DOI
https://doi.org/10.1007/978-3-319-63688-7_10