1. Introduction
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.
1.引言
现阶段的互联网商务变得几乎全部依赖金融机构作为可信第三方来处理电子支付。尽管对大多数交易来说，这个交易系统现阶段运行良好，但还是仍然存在这一些基于信任的交易方式本身固有的缺点。在这个系统中，因为金融机构不可避免要处理支付争端，所以全部不可逆的交易不能完全实现。而处理争端的所花费的费用势必要增加交易费用，这就限制了最小的交易金额，也减损了日常小额交易的可能性，第三方金融机构主导的为不可逆交易提供的不可逆支付的服务带来的能力减损也势必会推高交易成本。交易的可逆程度越高，达成交易的所需要的信任基础就越深厚。商家也就更加警惕他们的客户，向他们索取正常交易情况下并不需要的过多信息。人们也能接受一定比例的欺诈，并认为这是不可避免的。在使用实体货币、进行面对面交易支付的人们之间可以避免这些成本以及不确定性，但是除此之外迄今为止还没有出现一种不通过可信第三方的交易支付渠道。
我们需要的是一个基于加密证明而不是基于信任才产生的电子支付系统，在这个系统里，任何自愿一方都能够无需通过可信第三方而直接向另一方支付。交易因为在计算意义上的实际不可逆保护了卖家免受欺诈，无利害关系的第三方能够轻易的证明并保存交易情况这一特性也使得买家的权利能够得到保护。在这篇论文当中，我们提出一种解决双花问题的方案，这个方案采用的是点对点分散式时间戳服务器来产生交易的物理先后顺序的计算证明。只要诚实守信的节点联合起来控制着比攻击者很多的cpu算力，整个系统就是安全的。
（待续）
