ABSTRACT
This chapter presents a state-of-the-art in the area of Byzantine consensus and its application in blockchains. Bitcoin’s blockchain is a secure, unmodifiable, append-only, log of transactions, as mentioned before. This blockchain is executed in a set of nodes that run Bitcoin’s software and form a peer-to-peer network. Bitcoin’s blockchain may be said to implement a speculative variation of validity predicate-based consensus. Buterin created Ethereum as a platform for the implementation of smart contracts in a blockchain, using a cryptocurrency when necessary. Creating variants of Bitcoin and Nakamoto consensus is one of the more prolific research topic in the blockchain area, so this section will focus on some of the most relevant works. Sompolinsky and Zohar have shown that blockchains with many nodes and in which blocks are mined fast have high fork rates, allowing reasonably weak attackers to reverse payments they made.
