Electronic crypto-currencies such as bitcoin, and more generally the concept of a blockchain or distributed ledger, have the potential to revolutionise financial transactions and the role of financial institutions and regulators. This module will provide a foundation in the distributed ledgers and crypto-currencies, and will include the following topics: consensus in distributed systems, the CAP theorem, economic consensus, block-chains, Bitcoin, P2P contracts.

电子加密货币，像是比特币，是一种区块链或者是分布式帐的概念，是有潜力颠覆金融交易行业的。本栏目提供一些加密货币的基本知识。主要包括一下内容：分布式系统中的共识，CAP定理，经济共识，区块链，比特币，P2P合同。

我们需要注意几点：

- 这个领域比较新颖，大概是2008年兴起的

- 理论和技术仍然在融合，两者并未发展成熟，所以请学会质疑。

1 问题提出

我们理想的电子货币是要解决两个问题：

the e-money is authentic (not counterfeit) 电子货币是要被认证的。（不能伪造）
The same e-money cannot be spent more than once (double-spend porblem) 同一个电子货币不能被花费两次。

常见的解决方法就是：需要一个信得过的人或者机构去认证货币并且记录所有的交易者。

假设没有一个这样的人，怎么办呢？我们先记住这个问题

2 认识比特币

Bitcoin was first truly decentralized system for e-money比特币是第一个真正的电子货币去中心化系统
Asymmetric key cryptography
非对称密钥加密
性质：1.没有中央权威；2.去中心化；3.没有货币的双重支出；4.开放和公开；5.匿名（实际上是假名）
协议：Proof of Work（PoW）；Proof of Stake (PoS) ； Proof of Authority (PoA) ； Proof of Identity (PoI) ； Proof of Elapsed Time (PoET)

3 分布式账目技术

Distributed Ledger Technology (DLT)
All nodes on a distributed ledger agree on the values of the variable(s) on the ledger. They have a shared state.
The ledger also preserves past states (the history), so the protocol is stateful.
This property can prevent “double-spending” of some currency or asset.
这个技术适用于：Cryptocurrency transactions；Currency transactions；Transactions involving exchanges of ownership of assets；Promises and commitments

4 作业

List the sequence of events involved in acceptance of new blocks by nodes.
Describe the mathematical problems used in Bitcoin for PoW.
What is the total maximum number of Bitcoin to be issued? How many have been issued so far? What will miners be paid after the maximum is reached?
What is a wallet? What is the difference between wallets held on personal machines versus wallets held on an exchange?
List the major Bitcoin exchanges and their country of location. Is there a major exchange which has not been hacked at least once?

每周一篇博文，从零学习加密货币