Cryptology ePrint Archive: Report 2017/300
Tortoise and Hares Consensus: the Meshcash Framework for Incentive-Compatible, Scalable Cryptocurrencies
Iddo Bentov and Pavel Hubáček and Tal Moran and Asaf Nadler
Abstract: We propose Meshcash, a new framework for cryptocurrency protocols that combines a novel, proof-of-work based, permissionless
byzantine consensus protocol (the tortoise) that guarantees eventual consensus and irreversibility, with a possibly-faulty
but quick consensus protocol (the hare). The construction is modular, allowing any suitable ``hare'' protocol to be
plugged in. The combined protocol enjoys best of both worlds properties: consensus is quick if the hare protocol
succeeds, but guaranteed even if it is faulty. Unlike most existing proof-of-work based consensus protocols, our tortoise protocol does
not rely on leader-election (e.g., the single miner who managed to extend the longest chain). Rather, we use ideas from
asynchronous byzantine agreement protocols to gradually converge to a consensus.
Meshcash, is designed to be race-free: there is no ``race'' to generate the next block, hence honestly-generated blocks are always rewarded.
This property, which we define formally as a game-theoretic notion, turns out to be useful in
analyzing rational miners' behavior: we prove (using a generalization of the blockchain mining games
of Kiayias et al.) that race-free blockchain protocols are incentive-compatible and satisfy
linearity of rewards (i.e., a party receives rewards proportional to its computational power).
Because Meshcash can tolerate a high block rate regardless of network propagation delays (which will only affect latency), it
allows us to lower both the variance and the expected time between blocks for honest miners; together with linearity of
rewards, this makes pooled mining far less attractive. Moreover, race-free protocols scale more easily (in terms of
transaction rate). This is because the race-free property implies that the network propagation delays are not a factor in
terms of rewards, which removes the main impediment to accommodating a larger volume of transactions.
We formally prove that all of our guarantees hold in the asynchronous communication model of Pass, Seeman and shelat,
and against a constant fraction of byzantine (malicious) miners; not just rational ones.
Category / Keywords: cryptographic protocols / crypto-currency, bitcoin, consensus
Date: received 1 Apr 2017, last revised 3 Apr 2017
Contact author: talm at idc ac il
Available format(s): PDF | BibTeX Citation
Version: 20170407:024317 (All versions of this report)
Short URL: ia.cr/2017/300
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