We present Colordag, a blockchain protocol where following the prescribed strategy is, with high probability, a best response as long as all miners have less than 1/2 of the mining power. We prove the correctness of Colordag even if there is an extremely powerful adversary who knows future actions of the scheduler: specifically, when agents will generate blocks and when messages will arrive. The state-of-the-art protocol, Fruitchain, is an ε-Nash equilibrium as long as all miners have less than 1/2 of the mining power. However, there is a simple deviation that guarantees that deviators are never worse off than they would be by following Fruitchain, and can sometimes do better. Thus, agents are motivated to deviate. Colordag implements a solution concept that we call ε-sure Nash equilibrium and does not suffer from this problem. Because it is an ε-sure Nash equilibrium, Colordag is an ε-Nash equilibrium and with probability 1-ε is a best response.
@InProceedings{abraham_et_al:LIPIcs.DISC.2023.1, author = {Abraham, Ittai and Dolev, Danny and Eyal, Ittay and Halpern, Joseph Y.}, title = {{Colordag: An Incentive-Compatible Blockchain}}, booktitle = {37th International Symposium on Distributed Computing (DISC 2023)}, pages = {1:1--1:22}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-301-0}, ISSN = {1868-8969}, year = {2023}, volume = {281}, editor = {Oshman, Rotem}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.1}, URN = {urn:nbn:de:0030-drops-191272}, doi = {10.4230/LIPIcs.DISC.2023.1}, annote = {Keywords: Game theory, incentives, blockchain} }