Reaching consensus in a distributed decentralized system is difficult. The Bitcoin blockchain proposes a solution to the conensus problem that can scale to systems with thousands of nodes. Since then, many extensions and alternatives have been proposed targeting the improvement of system quality attributes such as performance, security, scalability and fault tolerance. Examples include: Pick one of the papers above and write an essay explaining the fundamental problem the blockchain is solving. Which components/parties are involved and how do they interact? Which system quality attributes are traded off? Are the claims about he quality attributes supported by experimental/theoretical evidence, and if so, then how convincing are these?