purely peer-to-peer version electronic cash allow online financial institution trusted third party prevent double-spending We propose a solution double-spending problem peer-to-peer network network timestamps transactions hashing them into an ongoing chain forming a record cannot be changed proof-of-work rejoin the network at will sent directly Digital signatures provide solution payments hash-based proof-of-work that without redoing serves proof sequence events witnessed largest pool of CPU power. power controlled nodes network itself requires minimal structure. Messages broadcast can leave Satoshi Nakamoto