a purely peer to peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial ins titution. digital signatures provide part of the solution, but the main benefits are lost if a trusted third party is still required to prevent doublespending.w e propose a solution to the doublespending problem using a peer to peer network. the network timestamps transactions by hashing them into an ongoing chain of has h based proofofwork, forming a record that cannot be changed without redoing the proof of work. the longest chain not only serves as proof of the sequence of ev ents witnessed, but proof that it came from the largest pool of cpu power. as lo ng as a majority of cpu power is controlled by nodes that are not cooperating to attack the network, theyll generate the longest chain and outpace attackers. th e network itself requires minimal structure. messages are broadcast on a best ef fort basis, and nodes can leave and rejoin the network at will, accepting the lo ngest proof of work chain as proof of what happened while they were gone.