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The consensus algorithm is responsible for the 3 critical aspects of blockchain technology – scalability, security and decentralization. Proof-of-Work (PoW) is the backbone of the Bitcoin blockchain, but it has been in existence even before the idea of Bitcoin came into existence. PoW is the choice of consensus algorithm for some of the largest market cap cryptocurrencies out there today, such as Bitcoin Cash. The total power involved in the mining of Bitcoin today is as high as the total energy consumption of the Czech Republic. Bitcoin suffers from a vulnerability called the 51% attack, if a single entity can control 51% of the total hash power of the network.