DETERMINING THE NUMBER OF CONFIRMATION BLOCKS IN A TWO-LEVEL BLOCKCHAIN WITH PROOF-OF-PROOF CONSENSUS PROTOCOL FOR DIFFERENT CONSENSUS TYPES IN MAINCHAIN/SIDECHAIN TO PREVENT DOUBLE-SPEND ATTACK II. PoW IN MAINCHAIN/PoS IN SIDECHAIN

Abstract

The paper investigates the issues of secure functioning of a two-level blockchain with a complex mixed consensus protocol — Proof-of-Work in the main blockchain (mainchain) and Proof-of-Stake in the secondary (sidechain). The principle of building such a blockchain is based on the Proof-of-Proof protocol, where a stable blockchain (mainchain) is used to ensure the stability of the sidechain, by referring the mainchain blocks to the sidechain blocks using special transactions. Such a structure allows for faster block generation in the sidechain and, accordingly, faster processing of transactions without reducing stability and without increasing the block size. In turn, such a two-level blockchain is of the greatest interest for the creation of a cascade system of state registers, which will be guaranteed to be protected against the substitution and forgery of documents. The main results of the work areexplicit analytical expressions for estimates of the probability of double spend attack on such a two-level blockchain, under the condition of an adversary in the sidechain and in the mainchain. The expressions obtained allow finding the number of confirmation blocks in the sidechain, which guarantees security against the attack with a probability no less than a preset value. Keywords: blockchain, mainchain, sidechain, cryptocurrencies, mining, Proof-of-Proof consensus protocol, double spend attack.