MIT-blockchain-three

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

1. 设计特征：密码学、时间戳等
2. 哈希函数、非对称密码学、数字签名等
3. 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

1. General properties:maps input x of any size to an output of fixed size—called a “hash”
2. Deterministic(不可逆转的)：always the same hash for the same x
3. 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

1. Preimage resistant (one way)：infeasible(不能办到的) to determine x from hash(x)
2. Collision resistant: infeasible to find x and y where hash(x)=hash(y)
3. Avalanche effect: change x slightly and hash(x) changes significantly
4. 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