Properties of money: Trust, store of value, acceptance
requirement: all computers must have the same "table" of who owns what
Double-spending attack: attacker sends two transactions to two different people to different nodes. if they just replicate, there is no way of knowing what the correct "state" of the network is
We need a Consesus Protocol
Consensus Protocol
Main idea: Agree on the majority
But most participants would need to be "friendly"
approach: use a random hash function, where it is extremely hard to find a collision