Commerce on the Internet has come to rely almost exclusively on financial institutions serving as trusted third parties to process electronic payments. While the system works well enough for most transactions, it still suffers from the inherent weaknesses of the trust based model. Completely non-reversible transactions are not really possible, since financial institutions cannot avoid mediating disputes. The cost of mediation increases transaction costs, limiting the minimum practical transaction size and cutting off the possibility for small casual transactions, and there is a broader cost in the loss of ability to make non-reversible payments for non-reversible services. With the possibility of reversal, the need for trust spreads. Merchants must be wary of their customers, hassling them for more information than they would otherwise need. A certain percentage of fraud is accepted as unavoidable. These costs and payment uncertainties can be avoided in person by using physical currency, but no mechanism exists to make payments over a communications channel without a trusted party.
What is needed is an electronic payment system based on cryptographic proof instead of 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 escrow mechanisms could easily be implemented to protect buyers. In this paper, we propose a solution to the double-spending problem using a peer-to-peer distributed timestamp server to generate computational proof of the chronological order of transactions. The system is secure as long as honest nodes collectively control more CPU power than any cooperating group of attacker nodes.
互联网商业几乎完全依赖金融机构作为可信第三方去处理电子支付。虽然针对大多数交易来说，这个系统还算不错，但，它仍然被基于信任的模型所固有的缺陷所拖累。完全不可逆转的交易实际上并不可能，因为金融机构不能避免仲裁争议。仲裁成本增加了交易成本，进而限制了最小可能交易的规模，且干脆阻止了很多小额支付交易。除此之外，还有更大的成本：系统无法为那些不可逆的服务提供不可逆的支付。逆转的可能性，造成了对于信任的需求无所不在。商家必须提防着他们的顾客，麻烦顾客提供若非如此（如若信任）就并不必要的更多信息。一定比例的欺诈，被认为是不可避免的。这些成本和支付不确定性，虽然在人与人之间直接使用物理货币支付的时候是可以避免的；但，没有任何一个机制能在双方在其中一方不被信任的情况下通过沟通渠道进行支付。
我们真正需要的是一种基于加密证明而非基于信任的电子支付系统，允许任意双方在不需要信任第三方的情况下直接交易。算力保障的不可逆转交易能帮助卖家不被欺诈，而保护买家的日常担保机制也很容易实现。在本论文中，我们将提出一种针对双重支出的解决方案，使用点对点的、分布式的时间戳服务器去生成基于算力的证明，按照时间顺序记录每条交易。此系统是安全的，只要诚实节点总体上相对于相互合作的攻击者掌握更多的 CPU 算力。
本节主要阐述了「区块链支付系统」相对「传统电子支付系统」的优势：
- 区块链支付系统降低了成本
- 买家无需提供过多信息，实现了一定程度上的匿名
- 提出了一种在没有被信任的第三方（中心）的情况下，也能解决双重支付问题的方案
大白话总结，即是： 传统的系统里，我和陌生人交易需要第三方（国家、机构）背书。而在这个系统里，背书的是系统本身的规则。