Block Chain Foundation (III.)

Lecture 3.1 Author: bao_zijian@163.com Bitcoin transactions append-only Ledger decentralized consensus-miners to validate Tran Sactions

Lecture 3.2 Author: bao_zijian@163.com Bitcoin scripts Output "addresses" are really to convert the address in output to the contract the scripts is th At the input address is also a script actually input scripts called scriptsig output scripts called Scriptpublic    Key forth language. is a stack-based language no loops a language similar to forth: simple, but support for pretty sophistcated cryptography there are Purpose instructions to did compute hash functions and to compute signatures and Verigy
Bitcoin Script Instructions 256 opcodes total (15disabled,75 reserved) operation that can be done: arithmetic If/then logic/ Date Handling Crypto

Lecture 3.3 Author: bao_zijian@163.com Applications of Bitcoin scripts
Example 1:escrow transactions (third party transaction) a third parties and do Ascrow transactions Multigis multiple signature technology
Example 2:green addresses has a bank. There are two companies in reality: Instawaller and Mount Gox

Example 3:efficient micro-payments Problem:alice wants to pay Bob for each minue of the phone service. She doesn ' t want to incur a transaction fee every. Solution:low value transaction every minute

Multi-palyer Lotteries
Lecture 3.4 Author: bao_zijian@163.com Bitcoin blocks why bundle transactions? Single, work for miners limit length of hash-chaina of blocks faster to verify history



Lecture 3.5 Author: bao_zijian@163.com The bitcoin network let us talk about how to Bitcoin blocks get put together. Bitcoin Peer-to-peer Network Ad-hoc Protocol (runs on TCP Port 8333) Ad-hoc network with random topology all nodes are equal new nod      ES can join at no time forget non-responding nodes after 3 hr should I relay a proposed transaction? Transaction valid with chain script matches a whitelist avoid unusual scripts Haven ' t seen b Eford Avoid infinite loops doesn;t conflict with others I ' ve relayed avoid double-spengs Race conditions De Fault behavior:accept What you hear a network position matters miners may implement other logic!
How is the network? Impossible to measure exactly estimates-up to 1M 1P addresser/month only about 5-10k ' full nodes ' permannently C Onnected fully-validate This number is dropping!
Lecture 3.6 Author: bao_zijian@163.com Limitations & Improvements 10min.average creation time per blocks 1M bytes in a bloc K
Througput limits in Bitcoin 7 transactions/sec compare To:visa,paypal
Cryptographic limits in Bitcoin only 1 signature Algorithm (ECDSA/P256) hard-coded hash functions
Hard-forking changes to Bitcoin
Next Week, we'll talk about Human beings aren ' t work for people, don't nodes how do people interact with the network? How does people exchange bitcoins for cash? How do people securely store bitcoins? Currency needs to work for people, not nodes.