Continuing the excellent series of Discovering Bitcoin, moving into the digital age, we have lost the most fundamental element of our money, it's "hardness." By what means can we get it back? Can we make a scarce money in the digital world, that has no authority, no ruler? Can we restore the freedom of decentralized money? Find out about the brilliant use of difficult puzzles, to achieve digital hardness, in part #5 of Giacomo's excellent series, "Digital Scarcity."