This document provides a comprehensive guide on implementing a blockchain using Python, discussing characteristics of blockchain, Python development environments, and creating a simple HTTP server. It includes practical exercises for designing transactions, making custom APIs, generating blocks, and validating blockchain data. The document also outlines procedures for managing transactions and interfacing between nodes for broadcasting block information.

1. BlockChain on Python
한국폴리텍대학(Korea Polytechnics)
스마트금융과(dept. of Smart Finance)

2. Overview
 Characteristics of blockchain
 Python
 Simple Http Server by Python
Make your own code and APIs
 Block, Hashing
 Transaction
Design your transaction model
 Making Block
 Merge with your BlockChain and Http Server
 Propagating Block to other nodes

3. Characteristic of BlockChain
 Transactions
 Blocks
 Snapshot or Chaining between Blocks
 Hash for a integrity
 Validating of existing Blocks
 Interface or Interact with other nodes
 etc…

4. Python
development environment
 Python
 Anaconda
 Jupyter
 Pycharm
 Ftp, Linux Server, REST Test Tool(ARC, Post Man, Fiddler,…)
 Git, File Compare Tools …

5. python http server

6. Simple HTTP Server
by Python (GET)
참조 : https://mafayyaz.wordpress.com/2013/02/08/writing-simple-http-server-in-python-with-rest-and-json/
참조 : https://docs.python.org/3/library/http.server.html?highlight=basehttprequesthandler#http.server.BaseHTTPRequestHandler

7. Simple HTTP Server
by Python (GET) – Review
 python 문자열 다루기 : split

8. Simple HTTP Server
by Python (GET) – Review
 좀 더 Python 한 방법은?

9. Practice #1
 사용자가 요청한 주소의 Query String을 분해하여 HTML로 리턴하시오.
예>
http://localhost:8080/api/v1/getrecord?city=seoul&zipcode=08206&mobile=01012341234&nickname=cat
위 요청에 대한 응답 (HTML)
city : seoul
zipcode : 08206
mobile : 01012341234
nickname : cat

10. Practice #2
 서버에서 python socket serve를 실행하자
 포트 번호 : 80 + 학번 끝 두자리로 설정
 116번 서버에 본인 작업 디렉토리에서 소켓 서버를 실행하고
http://192.168.110.116:80xx/api/v1/ping 을 호출했을 때 본문없이 200 응답을 리턴
예시> 학번 끝자리가 23번인 학생의 경우
본인의 소켓서버를 116번 서버의 /home/smrt0023/ 폴더에 업로드 
소켓서버를 실행(포트번호는 8023) 
교수가 http://192.168.110.116:8023/api/v1/ping 을 호출했을때 200 OK 응답을 주면 성공

11. Fiddler로 테스트하기
GET POST(application/json) POST(form based)

12. Postman 설치
 [H/W] 크롬 웹스토어에서 postman 으로 검색하고 설치 & 테스트

13. Simple HTTP Server
by Python (POST)
application/json;encode=utf-8
ctype pdict

14. Simple HTTP Server
by Python (POST)

15. Simple HTTP Server
by Python (POST)

16. Simple HTTP Server
by Python (POST)

17. Practice #3
 Make your own APIs on Development Server
 포트 번호 : 80 + 학번 끝 두자리로 설정
 API Spec 작성 및 테스트 결과를 Development Server에 업로드
- 업로드 위치 : /home/smrt00xx/…
- 실행 : python 000.py
- 테스트 : http://192.168.110.116:80xx/api/v1/addrecord
- API Spec. : API기본정보(요청URL, 포맷, 방식), 요청변수, 출력결과, 에러코드

18. Practice #3 (Cont.)
항목 정보 비고
요청URL http://192.168.110.116:80XX/api/v1/addrecord
요청Format JSON 형식
예> {“key1": [“value1",“value2"], “key2": “value1"}
요청Method POST
출력Format 입력요청한 JSON을 코드소유자 정보 추가하여 리턴
예> {“key1": [“value1",“value2"], “key2": “value1“, author:hwy}
결과code 성공시 200
실패시 403
…
 API Specification 예시

19. blockchain implementation on
python

20. Genesis Block
 6 Attributes
• Index – it’s position in the blockchain
• Previous Hash – the hash of the block that came before the current block
• Timestamp – the time the block was created
• Data – the information (e.g. transactions) that the block carries
• Hash – the hash of the block itself.
• proof – proof of work

21. 블록의 구조
class Block:
#A basic block contains, index (blockheight), the previous hash, a timestamp, tx information, a nonce, and the current hash
def __init__(self, index, previousHash, timestamp, data, proof, currentHash):
self.index = index
self.previousHash = previousHash
self.timestamp = timestamp
self.data = data
self.currentHash = currentHash
self.proof = proof
출처 : http://blockxchain.org/2017/06/04/simple-local-python-blockchain-pt1/
블록의 높이
거래 데이터
블록생성시점
이전블록의 해쉬값(이전블록의 연결고리, 스냅샷)
현재 블록의 해쉬값
작업증명 값( XX횟수)

22. 블록데이터 리턴
 Sequence Diagram
readBlockchain
블록체인 DB가 존재한다면?
if yes, DB를 읽어서 return
else 빈 데이터를 return

23. Source Code
 API Interface

24. Source Code
블록체인 DB가 존재한다면?
if yes, DB를 읽어서 return
블록체인 DB가 존재 X
빈 데이터를 return

25. At the moment,
블록데이터가 없는 상황
 블록데이터 생성이 필요
 신규API를 생성하여 Genesis Block을 생성해야 함
~/block/generateBlock를 추가하자
 블록을 구성할 데이터(Transaction Data)는 어떻게 구성할 것인가?
일단은, 임시 랜덤데이터를 구성하자
transaction = 'UserID ' + str(txFrom) + " sent " + str(amount) + ' bitTokens to UserID ' + str(txTo) + ". “
차후, 개인 또는 그룹별 블록체인 비즈니스 아이디어를 반영한 트랜잭션으로 수정예정

26. Source Code
(~/block/generateBlock)
 API Interface

27. 블록데이터 생성 흐름
getTxDatareadBlockchainmineNewBlock
블록체인 DB가 존재한다면?
if yes, DB를 읽어서 return
else, “Genesis Block” 생성하여 return
calculateHashgenerateNewBlock writeBlockchain
해쉬값이 우리가 정한 난이도와 일치한다면?
if yes, 블록체인 기록
else, generateNewBlock 반복

28. mineNewBlock
def mineNewBlock(difficulty = 5, blockchainPath = 'blockchain.csv'):
blockchain = readBlockchain(blockchainPath)
txData = getTxData()
timestamp = time.time()
proof = 0
newBlockFound = False
print('Mining a block...')
while not newBlockFound:
#print("Trying new block proof...")
newBlockAttempt = generateNextBlock(blockchain, txData, timestamp, proof)
if newBlockAttempt.currentHash[0:difficulty] == '0'*difficulty:
stopTime = time.time()
timer = stopTime - timestamp
print('New block found with proof', proof, 'in', round(timer, 2), 'seconds.')
newBlockFound = True
else:
proof += 1
blockchain.append(newBlockAttempt)
writeBlockchain(blockchain)
def mine(blocksToMine = 5):
for _ in range(blocksToMine):
mineNewBlock()
출처 : http://blockxchain.org/2017/06/04/simple-local-python-blockchain-pt1/

29. readBlockchain

30. getTxData (old)

31. def getLatestBlock(blockchain):
return blockchain[len(blockchain)-1]
def generateNextBlock(blockchain, blockData, timestamp, proof):
previousBlock = getLatestBlock(blockchain)
nextIndex = int(previousBlock.index) + 1
nextTimestamp = timestamp
nextHash = calculateHash(nextIndex, previousBlock.currentHash, nextTimestamp, proof, blockData)
return Block(nextIndex, previousBlock.currentHash, nextTimestamp, blockData, proof, nextHash)
배열
출처 : http://blockxchain.org/2017/06/04/simple-local-python-blockchain-pt1/
generateNextBlock

32. def calculateHash(index, previousHash, timestamp, data, proof):
value = str(index) + str(previousHash) + str(timestamp) + str(data) + str(proof)
sha = hashlib.sha256(value.encode('utf-8'))
return str(sha.hexdigest())
Hash 대상 : 현재 블록의 인덱스 + 이전 블록의 Hash + 현 블록의 TimeStamp + 현 블록의 거래데이터 + PoW(#)
출처 : http://blockxchain.org/2017/06/04/simple-local-python-blockchain-pt1/
calculateHash

33. writeBlockchain

34. Genesis Block
 Now we can create genesis block.
def getGenesisBlock():
timestamp = time.time()
print("# timestamp를 찍어본다.")
print("time.time() => %f n" % timestamp)
tempHash = calculateHash(0,'0',timestamp,"My very first block",0)
print(tempHash)
return Block(0, '0', timestamp, "My very first block", 0, tempHash)
blockchain = [getGenesisBlock()]
출처 : http://blockxchain.org/2017/06/04/simple-local-python-blockchain-pt1/
DB에 생성된 블록이 없을 경우 호출됨
현 블록의 해쉬값을 생성
(index, previousHash, timestamp, data, proof)

35. 테스트

36. 블록체인 데이터 조회하기
 블록데이터 조회
~/block/getBlockData로 조회하자

37. So far we can
 Create a genesis block
 Hash blocks
 Create additional blocks

38. Practice #3
 Design Your Own Transaction Data

39. Validation Blockchain

40. 이제 검증을 위한 API를 추가해 봅시다.
 검증로직 설계
 신규API를 생성하여 검증대상인 블록체인 데이터를 받아야 함(POST)
~/block/validateBlock/를 추가하자
- input과 output은 어떻게 설계해야 하는가?

41. Validation Blocks
출처 : http://blockxchain.org/2017/06/04/simple-local-python-blockchain-pt1/

42. Validation Blocks
출처 : http://blockxchain.org/2017/06/04/simple-local-python-blockchain-pt1/

43. Validation Blocks
def isValidChain(bcToValidate):
genesisBlock = []
bcToValidateForBlock = []
# Read GenesisBlock
try:
with open('blockchain.csv', 'r') as file:
blockReader = csv.reader(file)
for line in blockReader:
block = Block(line[0], line[1], line[2], line[3], line[4], line[5])
genesisBlock.append(block)
break
except:
print("file open error in isValidChain")
pass
# transform given data to Block object
for line in bcToValidate:
# print(type(line))
# index, previousHash, timestamp, data, currentHash, proof
block = Block(line['index'], line['previousHash'], line['timestamp'], line['data'], line['currentHash'], line['proof'])
bcToValidateForBlock.append(block)
#if it fails to read block data from db(csv)
if not genesisBlock:
print("fail to read genesisBlock")
return False
# compare the given data with genesisBlock
if not isSameBlock(bcToValidateForBlock[0], genesisBlock[0]):
print('Genesis Block Incorrect')
return False
tempBlocks = [bcToValidateForBlock[0]]
for i in range(1, len(bcToValidateForBlock)):
if isValidNewBlock(bcToValidateForBlock[i], tempBlocks[i - 1]):
tempBlocks.append(bcToValidateForBlock[i])
else:
return False
return True
CSV REST Call
Genesis
Block
Genesis
Block
=

44. 테스트

45. Practice #4
 Design Post API of a new transaction data

46. manage transactions

47. Transaction Data
 As-Is Transaction Data (5 random data)
“UserID <random number> sent <random number> bitTokens to UserID <random number>.”
 To-Be Transaction Data
index currentHash timestamp transaction data
<<Block>>
<<Transactions>>
commitYN sender amount receiver UUID(unique #)
채굴포함여부

48. class txData
 5 attributes
블록 포함여부(채굴) : commitYN
송신자 : sender
금액 : amount
수신자 : receiver
고유식별값 : uuid
class txData:
def __init__(self, commitYN, sender, amount, receiver, uuid):
self.commitYN = commitYN
self.sender = sender
self.amount = amount
self.receiver = receiver
self.uuid = uuid

49. POST API 추가하기
(transaction data)

50. Transaction Data
(Dictionary  Instance of class txData)
import uuid 필요
예> 369a1e95-3723-4b26-8ab8-9bcc2c5938f0

51. Write
Transaction
Data
<<temp csv>><<txData csv>>
new tx data
<<temp csv>> <<txData csv>>

52. getTxData 수정
예> [6b3b3c1e-858d-4e3b-b012-8faac98b49a8]UserID hwang sent 333 bitTokens to UserID kim.

53. read txData from csv

54. Update txData of csv #1
(when it has been mined)
 채굴되었다면?

55. Update txData of csv #2
정규표현식
row[4]row[0]

56. 테스트

57. Practice #5
 Design Post API of a sending transaction data

58. Broadcast

59. set up
 library, global variables
타 노드로 채굴 정보를 POST하기 위한 라이브러리
노드간 인터페이스 API
노드 정보(서버IP, Port) 를 저장하는 파일

60. broadcast block when it mined
타 노드로 전파

61. broadcastNewBlock
방금 채굴된 블록을 포함한 블록체인 정보를
인접 노드의 API(receiveNewBlock)로
POST 호출하여 전달

62. readNodes
노드 정보(서버IP, Port) 를 읽어오기

63. addNode
http://localhost:8099/node/addNode?127.0.0.1:8096

64. addNode

65. receive new block info
g_receiveNewBlock = "/node/receiveNewBlock"

66. compare blockchain info
 latest block +1 != broadcasted last block
latest block == broadcasted last block
latest block +1 < broadcasted last block
latest block +1 > broadcasted last block
 latest block +1 == broadcasted last block

67. compare and merge

68. ExceptionalCase

69. ExceptionalCase

70. ExceptionalCase

71. initSvr (1/2)
 인접 노드 정보 구하기

72. initSvr (2/2)
 블록체인 정보 구하기
g_bcFileName = "blockchain.csv"

73. 붙임

74. related sites…
 __dict__ 설명 : https://wikidocs.net/1743
 json.dump 설명 : http://pythonstudy.xyz/python/article/205-JSON-%EB%8D%B0%EC%9D%B4%ED%83%80
https://kimdoky.github.io/python/2017/11/11/library-book-chap8-4.html
https://docs.python.org/3/library/json.html
 람다식 설명 : https://wikidocs.net/64

75. 정규표현식(Regular Expression)
돌아가기

76. 정규표현식(Regular Expression)