Paper 2018/415

Flux: Revisiting Near Blocks for Proof-of-Work Blockchains

Alexei Zamyatin, Nicholas Stifter, Philipp Schindler, Edgar Weippl, and William J. Knottenbelt


The term near or weak blocks describes Bitcoin blocks whose PoW does not meet the required target difficulty to be considered valid under the regular consensus rules of the protocol. Near blocks are generally associated with protocol improvement proposals striving towards shorter transaction confirmation times. Existing proposals assume miners will act rationally based solely on intrinsic incentives arising from the adoption of these changes, such as earlier detection of blockchain forks. In this paper we present Flux, a protocol extension for proof-of-work blockchains that leverages on near blocks, a new block reward distribution mechanism, and an improved branch selection policy to incentivize honest participation of miners. Our protocol reduces mining variance, improves the responsiveness of the underlying blockchain in terms of transaction processing, and can be deployed without conflicting modifications to the underlying base protocol as a velvet fork. We perform an initial analysis of selfish mining which suggests Flux not only provides security guarantees similar to pure Nakamoto consensus, but potentially renders selfish mining strategies less profitable.

Available format(s)
Cryptographic protocols
Publication info
Bitcoinproof-of-workweak blocksvelvet fork
Contact author(s)
a zamyatin @ imperial ac uk
2018-05-29: last of 2 revisions
2018-05-10: received
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      author = {Alexei Zamyatin and Nicholas Stifter and Philipp Schindler and Edgar Weippl and William J.  Knottenbelt},
      title = {Flux: Revisiting Near Blocks for Proof-of-Work Blockchains},
      howpublished = {Cryptology ePrint Archive, Paper 2018/415},
      year = {2018},
      note = {\url{}},
      url = {}
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