[정보 보안] Business Chances of Blockchain (11)

[4] Business Chances of Blockchain

Block이란?
- Record of state change
- Consisting of hash, answer, and transactions
- Hash : Summary of previous transaction information
- Answer : Value used for hash calculation
- Transaction : 거래정보
- Transaction records are stored in blocks.

Blockchain이란?
- A fully distributed P2P software network
- That uses encryption to secure host applications, stores data, and transfers real world monetary values digitally.
- The blocks are connected by cryptographic technology.
- Technical : Backend DB that maintains a publicly distrubuted ledger
- Buisness : An exchange network that implements movement of value assets between individuals
- Legal : Dealer-free transaction verification solution

Blockchain Component
- Smart contract
- Digital signature and hash algorithm
- Consensus algorithm

Blockchain = Distributed Ledger
- Includes financial and non-financial transactions
- Replicated to multiple systems in near real time over P2P network.
- All participants own copies of the same ledger and receive updates when transactions are added.
- All participants will help determine the intrinsic invariance of all existing records.
- Prove identity, authenticity, and read/write access using cryptography and digital signatures.
- Easy to detect when to change past records.

Blockchain Core Technology
- Digital Signature
- Hash Algorithm
- P2P Network

@Digital Signature : Electronic Signature(simplified)
- 1. Message를 Hash돌리고
- 2. Hash digest를 priavate key로 암호화 한다.
- 3. Message + encrypted digest를 전송한다.
- 4. 받았으면 받은 digest를 public key로 복호화하고
- 5. Message를 Hash 돌린 후,
- 6. Hash digest와 복호화한 digest와 비교한다.

@Hash Algorithm
- Output value of the same length for all inputs
- MD5, SHA-512, SHA-2, SHA-3

@P2P Network
- Ensure stability by ensuring participants in the network share all transaction records.

Blockchain Issue
- 1. The Byzantine General Problem
- 명령이 겹치면 뭘 수행해야하는가
- 2. Double Spending Problem (Finalize Problem)
- Digital money system consumes more than one token
- Hard to determine the transaction finalization for the transaction

Blockchain Classification
- Public : anyone can participate in notarization through computing power
- Private + Consortium : one entry manages the internal network as a blockchain

Cryptocurrency(Blockchain 1.0)
- Bitcoin is electronic currency, cryptocurrency, etc.
- Issuing authority : any
- Currency Type : digital
- Applicable laws : none
- Usage : franchisee
- Exchangeability with legal currency : freely exchanged

Bitcoin's Goal
- Pure P2P version electronic money
- Allow online payment to be transferred directly from one party to another without going through a finalcial institution.

Technical Issues to be solved for online electronic money exchange
- Exchange of electronic money 
-> Transactions that change the name from the previous owner to another owner

- Requires previous owner's identification and non-reputation
-> Digital Signature

- It is difficult to prove that money received in the past has not been used twice
-> Blockchain based on hash values

- Manipulating the whole blockchain issuees
-> Introduced a method to solve large-scale computatio problems to create new blocks

- Requiring a lot of CPU power to create a block
-> Provide incentives

- The blockchain is branched according to the block generation time and the network propagation time
-> Adopt the longest block chain (longer legs)

Miners
- A cryptographic supporter who operates an Ethereum node at home, verifying the order of transactions, takes an Ether token in return
- Mining : collective effort of a mining network block verification
- Mining of individual nodes collectively keeps the network secure

Components of Candidate Blocks for Block Verification
- Transaction hash of block
- The root hash of the entire block chain
- Block number since chain started
- Difficulty of the block

How consensus works
- Block header : timestamp, hash value of previous block header, nonce, root mercury tree
- 1. Proof of Work
- hash value of previous block header(SHA256) + nonce + root mercury tree를 SHA256으로 해쉬 돌린 후
- 결과가 Goal Value보다 작거나 같다면, 새로운 블럭 생성
- 이 때, password hash value가 target value보다 크다면, nonce는 re-steered.
- 2. Block Propagation
- Wallet issues transactions and broadcasts to all participants
- Miner calculates the hash
- 먼저 푸는 순서대로 n번째 node가 된다.
- Provide compensation to the perso who resolved the problem quickly

Smart Contract(Block Chain 2.0)
- Alternative for traditional services
- A unit of application operating on a blockchain (Ethereum Virtual Machine-specific binary format)
- To provide better security than existings
- To offer lower processing costs than existings

- The development and usage flow of smart contract is the same as web application.
- Developer : deploy web server (deploy block chain)
- User : access the server through browser

Ethereum
- An open source project developed by the Swiss non-profit Ethereum Foundation.
- A block-chain technology that can be implement smart contracts with simple code.
- Distributed platform for smart contracts
- Contracts

Swarm
- Distributed repository and distributed content delivery platform.
- Save large size data such as medical data
- Net / file store

Whisper
- Destributed communication protocol for message delivery.
- Lightweight data transfer channels that help dApps communicate with each other and have greater impact.
- Dynamic comms

Blockchain 1.0 vs. Blockchain2.0
- Bitcoin application(BitcoinCore) vs. various application
- A system that automatically moves digital assets based on predefined rules.
- If only the network is running, its execution and asset movement is automatically performed by the system.

Blockchain Service and Chanllenges
- Blockchain-based services may appear to be an adjunct to replacing exising mainstream services.
- However, as the number of users increases, they enter the main stream.