Analysis of bitcoin backbone protocol in the non-flat model

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.