Assuming honest participation, however, is a strong assumption, especially in a setting where honest players are expected to perform a lot of work (to solve the computational puzzles). In Nakamoto's Bitcoin application of the blockchain protocol, players are incentivized to solve these puzzles by receiving rewards for every ``blocks'' (of transactions) they contribute to the blockchain. An elegant work by Eyal and Sirer (FinancialCrypt'14), strengthening and formalizing an earlier attack discussed on the Bitcoin forum, demonstrates that a coalition controlling even a minority fraction of the computational power in the network can gain (close to) 2 times its ``fair share'' of the rewards (and transation fees) by deviating from the protocol instructions. In contrast, in a fair protocol, one would expect that players controlling a $\phi$ fraction of the computational resources to reap a $\phi$ fraction of the rewards.
In this work, we present a new blockchain protocol---the FruitChain protocol---which satisfies the same consistency and liveness properties as Nakamoto's protocol (assuming an honest majority of the computing power), and additionally is $\delta$-approximately fair: with overwhelming probability, any honest set of players controlling a $\phi$ fraction of computational power is guaranteed to get at least a fraction $(1 - \delta) \phi$ of the blocks (and thus rewards) in any $Omega( \kappa/\delta )$ length segment of the chain (where $\kappa$ is the security parameter).
As a consequence, if this blockchain protocol is used as the ledger underlying a cryptocurrency system, where rewards and transaction fees are evenly distributed among the miners of blocks in a length kappa segment of the chain, no coalition controlling less than a majority of the computing power can gain more than a factor $(1 + 3\delta)$ by deviating from the protocol (i.e., honest participation is an $n/2$-coalition-safe $3\delta$-Nash equilibrium).
Finally, the fruit chain protocol enables decreasing the variance of mining rewards and as such significantly lessens (or even obliterates) the need for mining pools.Category / Keywords: cryptographic protocols / Consensus, blockchains, distributed systems, fairness, cryptocurrency Date: received 21 Sep 2016, last revised 9 Oct 2016 Contact author: runting at gmail com Available format(s): PDF | BibTeX Citation Version: 20161009:070340 (All versions of this report) Short URL: ia.cr/2016/916 Discussion forum: Show discussion | Start new discussion