原始文献 / 邮件 / Bitcoin P2P e-cash paper
Bitcoin P2P e-cash paper
Cryptography Mailing List · 2008-11-03 01:37:43 UTC
Satoshi Nakamoto 写道：
> 我一直在研究一种新型电子现金系统，它完全是点对点的，没有可信第三方。
>
> 论文地址：
> http://www.bitcoin.org/bitcoin.pdf
我们非常、非常需要这样一个系统，但就我对您提案的理解，它似乎无法扩展到所需的规模。
可转让的工作量证明代币要有价值，必须具有货币价值。要具有货币价值，必须在一个非常大的网络中流通——例如类似 bittorrent 的文件交易网络。
要及时发现并拒绝双重支付事件，必须掌握交易中币的大部分历史交易，若天真地实现，这要求每个节点掌握大部分历史交易，或大部分近期历史交易。如果有数亿人进行交易，那需要大量带宽——每个节点必须知道全部或相当大的一部分。
早在网络规模接近那个程度之前，用户就可以安全地使用简化支付验证（第8节）来检查双重支付，该方法只需要拥有区块头链，每天约12KB。只有试图创造新币的人才需要运行网络节点。起初，大多数用户会运行网络节点，但随着网络增长超过某个规模，这将越来越多地留给拥有专用硬件服务器农场的专家。一个服务器农场只需要在网络上有一个节点，局域网内的其余部分都连接到这个节点。
带宽可能并不像您想的那么高。一笔典型的交易大约400字节（ECC相当紧凑）。每笔交易需要广播两次，姑且按每笔交易1KB计算。Visa在2008财年处理了370亿笔交易，即平均每天1亿笔。这么多交易需要100GB带宽，相当于12张DVD或2部高清电影的容量，按当前价格约值18美元带宽费。
如果网络真发展到那么大，需要数年时间，到那时，通过互联网传输2部高清电影可能算不上什么大事。
Satoshi Nakamoto
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英文原文
Satoshi Nakamoto wrote:
> I've been working on a new electronic cash system that's fully
> peer-to-peer, with no trusted third party.
>
> The paper is available at:
> http://www.bitcoin.org/bitcoin.pdf
We very, very much need such a system, but the way I understand your
proposal, it does not seem to scale to the required size.
For transferable proof of work tokens to have value, they must have
monetary value. To have monetary value, they must be transferred within
a very large network - for example a file trading network akin to
bittorrent.
To detect and reject a double spending event in a timely manner, one
must have most past transactions of the coins in the transaction, which,
naively implemented, requires each peer to have most past
transactions, or most past transactions that occurred recently. If
hundreds of millions of people are doing transactions, that is a lot of
bandwidth - each must know all, or a substantial part thereof.
Long before the network gets anywhere near as large as that, it would be safe for users to use Simplified Payment Verification (section 8) to check for double spending, which only requires having the chain of block headers, or about 12KB per day. Only people trying to create new coins would need to run network nodes. At first, most users would run network nodes, but as the network grows beyond a certain point, it would be left more and more to specialists with server farms of specialized hardware. A server farm would only need to have one node on the network and the rest of the LAN connects with that one node.
The bandwidth might not be as prohibitive as you think. A typical transaction would be about 400 bytes (ECC is nicely compact). Each transaction has to be broadcast twice, so lets say 1KB per transaction. Visa processed 37 billion transactions in FY2008, or an average of 100 million transactions per day. That many transactions would take 100GB of bandwidth, or the size of 12 DVD or 2 HD quality movies, or about $18 worth of bandwidth at current prices.
If the network were to get that big, it would take several years, and by then, sending 2 HD movies over the Internet would probably not seem like a big deal.
Satoshi Nakamoto
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