Nowadays, it is crucial to ensure the secrecy of shared data and the validity of received information. This is the case of money exchange between two different parties, in which one must keep the data of its own bank account hidden, or the exchange of information in the military field, where an interception must be prevented. For such reasons, cryptography was born. Because of its primary characteristic of assuring secrecy and reliability, one of its main applications regards blockchains: a network composed of people who do not know or trust each other uses it to ensure valid transactions. In 2009, Bitcoin was developed: a shared, permissionless blockchain whose structure and integrity are based on a Proof of Work (PoW) protocol.