{
  "Btc": "Bitcoin: A Peer-to-Peer Electronic Cash System\nSatoshi Nakamoto\nsatoshin@gmx.com\nwww.bitcoin.org\nAbstract. A purely peer-to-peer version of electronic cash would allow online\npayments to be sent directly from one party to another without going through a\nfinancial institution. Digital signatures provide part of the solution, but the main\nbenefits are lost if a trusted third party is still required to prevent double-spending.\nWe propose a solution to the double-spending problem using a peer-to-peer network.\nThe network timestamps transactions by hashing them into an ongoing chain of\nhash-based proof-of-work, forming a record that cannot be changed without redoing\nthe proof-of-work. The longest chain not only serves as proof of the sequence of\nevents witnessed, but proof that it came from the largest pool of CPU power. As\nlong as a majority of CPU power is controlled by nodes that are not cooperating to\nattack the network, they'll generate the longest chain and outpace attackers. The\nnetwork itself requires minimal structure. Messages are broadcast on a best effort\nbasis, and nodes can leave and rejoin the network at will, accepting the longest\nproof-of-work chain as proof of what happened while they were gone.\n1. Introduction\nCommerce on the Internet has come to rely almost exclusively on financial institutions serving as\ntrusted third parties to process electronic payments. While the system works well enough for\nmost transactions, it still suffers from the inherent weaknesses of the trust based model.\nCompletely non-reversible transactions are not really possible, since financial institutions cannot\navoid mediating disputes. The cost of mediation increases transaction costs, limiting the\nminimum practical transaction size and cutting off the possibility for small casual transactions,\nand there is a broader cost in the loss of ability to make non-reversible payments for nonreversible services. With the possibility of reversal, the need for trust spreads. Merchants must\nbe wary of their customers, hassling them for more information than they would otherwise need.\nA certain percentage of fraud is accepted as unavoidable. These costs and payment uncertainties\ncan be avoided in person by using physical currency, but no mechanism exists to make payments\nover a communications channel without a trusted party.\nWhat is needed is an electronic payment system based on cryptographic proof instead of trust,\nallowing any two willing parties to transact directly with each other without the need for a trusted\nthird party. Transactions that are computationally impractical to reverse would protect sellers\nfrom fraud, and routine escrow mechanisms could easily be implemented to protect buyers. In\nthis paper, we propose a solution to the double-spending problem using a peer-to-peer distributed\ntimestamp server to generate computational proof of the chronological order of transactions. The\nsystem is secure as long as honest nodes collectively control more CPU power than any\ncooperating group of attacker nodes.\n"
}