Number of Confirmation Blocks for Bitcoin and GHOST Consensus Protocols on Networks

Abstract

A specific number of transaction confirmation blocks determines average time of receiving and accepting payments at cryptocurrencies, and the shortest confirmation time for the same level of blockchain security provides the best user properties. Existing papers on transaction confirmation blocks for Bitcoin use implicit assumption of prompt spreading of Bitcoin blocks over the network (that is not always the case for the real world conditions). The newer publications with rigorous analysis and proofs of Bitcoin blockchain properties that take into account network delays provide asymptotic estimates, with no specific numbers for transaction confirmation blocks. We propose three methods for determination of required number of confirmation blocks for Bitcoin and GHOST on networks with delayed message delivery with different models that take into account the possibility of faster adversarial node syncronization. For the GHOST we propose the first (to our knowledge) strict theoretical method that allows to get required number of confirmation blocks for a given attacker’s hashrate and attack success probability.