MIT-blockchain-three
This lesson is about Blockchai Basics and Cryptography
本课程是的主要内容是区域链基础和密码学
Communications and computation that needs to be protected or verified, have some form of cryptographic algorithm,which happens to called a cryptographic primitive.
- communications
- computation
- semester
Study Question
- 设计特征：密码学、时间戳等
- 哈希函数、非对称密码学、数字签名等
- 双花问题double-spending
Double spending is when you have a piece of information and you use it twice.
Blockchain technical Features
- 基于密码学的哈希函数
- 时间戳日志
- 区块头和默克尔树
- 非对称密码学和数字签名
Cryptography
it`s not just communication in the presence of adversaries, it is also computation in the presence of adversaries.
Cryptographic hash functions
It is digital fingerprints for data
General properties
- General properties:maps input x of any size to an output of fixed size—called a “hash”
- Deterministic(不可逆转的)：always the same hash for the same x
- Efficiently computed高效计算：couple for terahashes a second.it is remarkly efficient algorithm.
if you take a certain set of data, it will always give you the same hash.
Crytographic properties
- Preimage resistant (one way)：infeasible(不能办到的) to determine x from hash(x)
- Collision resistant: infeasible to find x and y where hash(x)=hash(y)
- Avalanche effect: change x slightly and hash(x) changes significantly
- Puzzle friendless: knowing hash(x) and part of x it is still very hard to find rest of x
Timestamped append-only log-blackchain
Block header
- Version
- Previous block hash
- Merkle Root hash
- Timestamp
- Difficulty target
- Nonce
每10分钟产生一个区块头，时间越长越难产生
