Internet commerce has relied almost exclusively on financial institutions that serve as trusted third parties to process electronic payments. While the system works well for most operations, it still suffers from the shortcomings inherent in the trust-based model.
Completely non-reversible transactions are not possible, as financial institutions cannot avoid conflict mediation. The cost of mediation increases transaction costs, which limits the practical minimum transaction size and eliminates the possibility of occasional small transactions, and there is a broader cost in losing the ability to make non-reversible payments for non-reversible services. With the possibility of reversal, the need for trust spreads.
Merchants should be wary of their customers, pestering them for more information than they would otherwise need. A certain percentage of fraud is accepted as inevitable. These costs and payment uncertainties can be avoided live using physical currency, but there is no mechanism for making payments over a communication channel without a trusted party.
What is needed is an electronic payment system based on cryptographic proof rather than trust, allowing any two willing parties to transact directly with each other without the need for a trusted third party. Transactions that are computationally impractical to reverse would protect sellers from fraud, and routine dispute mechanisms could easily be implemented to protect buyers. In this article, we propose a solution to the double spend problem by using a peer-to-peer distributed time server to generate computational proof of the chronological order of operations.
The system is secure as long as honest nodes collectively control more CPU power than any cooperative group of attacking nodes.