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SCIENCE CHINA Information Sciences, Volume 63, Issue 3: 130105(2020) https://doi.org/10.1007/s11432-019-2698-1

Analysis of bitcoin backbone protocol in the non-flat model

Peifang NI1,2,3, Hongda LI1,2,3,*, Dongxue PAN1,2,3
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  • ReceivedJun 15, 2019
  • AcceptedOct 30, 2019
  • PublishedFeb 11, 2020

Abstract

Owing to the novel proof-of-work based consensus algorithm, bitcoin has been the most successful decentralized cryptocurrency so far. In bitcoin system, parties (miners) compete to create blocks by doing publicly verifiable proofs of sequential work (proof-of-work) and the probability that a party wins the competition is proportional to the amount of computational power that he has invested. Note that its security holds under honest majority assumption in terms of the amount of computational power. In this paper, we provide the formal analysis of bitcoin backbone protocol in the non-flat model. Precisely, we rethink and redefine the model of computing puzzles to capture the real-world protocol execution, where each party owns different amount of computational power and does sequential computations towards a puzzle independently. Fortunately, our work obtains the better results in analyzing the security of bitcoin backbone protocol, which can reflect the real-world protocol execution better, without any additional assumptions but the honest majority assumption. Finally, we show that a robust public transaction ledger can be built on top of bitcoin backbone protocol in our model securely.


Acknowledgment

This work was supported by National Key RD Program of China (Grant No. 2017YFB0802500) and Beijing Municipal Science and Technology Project (Grant No. Z191100007119007).


Supplement

Appendix A.


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  • Table 1   The parameters and symbols used in our analysis$^{\rm~a)}$
    ParameterDescription
    $k$Security parameter
    $\lambda$The proportion of honest parties in number
    $\lambda'$The proportion of honest parties in the amount of computational power
    $\delta$The advantage of honest parties, ($\lambda'>\frac{1}{1-\delta}$)
    $(\Delta,s)$Determines how the amount of computational power fluctuates across rounds
    $\varepsilon$Determines the amount of computational power in a valid block
    $\varphi$The distance between variable and expectation in standard execution
    $K'$The number of consecutive blocks for recalculating difficult target
    $t$The number of consecutive rounds for chain-growth property
    $l$The number of consecutive blocks for chain-quality property
    $K$The number of consecutive blocks for common-prefix property

    a

  • Table 2   The execution environments of analytical models
    Environment Ref. [4]Ref. [5] Ref. [6]Ours
    Permissionless setting No No YesNo
    Asynchronous network No Yes NoNo
    Non-flat parties No NoNoYes
    AssumptionsHMA and SA HMA and SAHMA and SAHMA
  • Table 3   The comparison of results between and ours
    Parameter Ref. [4] Ours
    HPoHP $\alpha''~=~\frac{q(n-t)}{1+pq(n-t)}$$\alpha\geq\frac{q(n-t)}{1+pc'}$
    HPoA $\beta''=qt$ $\beta=qt$
    CGR $g'=(1-\varphi)\alpha''$ $g=(1-\varphi)\alpha$
    CQ $\mu'=(1+\frac{\delta}{2})\frac{t}{n-t}$ $\mu=(1-\delta)\frac{t}{n-t}$

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