Java로 배워보는 BlockChain

02 May 2018 java java block_chain

해당 내용은 공부하면서 간단하게 만들어본 블록체인 입니다.

1. Block 만들기

BlockChain을 구성하는 Block 을 생성한다,
Block은 BlockChain 내에서 고유한 Hash(Digital Signature)값을 가지고 있다.
Block 내에는 이전 Block의 Hash 값과 데이터들이 포함되어 있다.

1) 소스코드

package kr.geun.o.bc.basic;

import java.util.Date;

/**
 * Block Class
 *
 * @author akageun
 */
public class Block {

   private String hash;
   private String previousHash;

   private String data;
   private long timeStamp;

   private Block() {

   }

   /**
    * Block Constructor
    *
    * @param data
    * @param previousHash
    */
   public Block(String data, String previousHash) {
      this.data = data;
      this.previousHash = previousHash;

      this.timeStamp = new Date().getTime();
   }

   /**
    * get previousHash
    *
    * @return
    */
   public String getPreviousHash() {
      return previousHash;
   }

   /**
    * get Hash
    *  - digital signature
    *
    * @return
    */
   public String getHash() {
      return hash;
   }

   /**
    * get TimeStamp
    *
    * @return
    */
   public long getTimeStamp() {
      return timeStamp;
   }

   /**
    * get Data
    *
    * @return
    */
   public String getData() {
      return data;
   }
}

2. Hash(Digital Signature) 생성 메소드 만들기

Sha256을 사용.

package kr.geun.o.bc.basic;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * BlockChain Utils
 *
 * @author akageun
 */
public class BcUtils {

   /**
    * Hash 생성
    *
    * @param inputValues
    * @return
    */
   public static String generateHash(String... inputValues) {
      try {
         StringBuffer sb = new StringBuffer();
         for (String inputValue : inputValues) {
            sb.append(inputValue);
         }

         String input = sb.toString();

         MessageDigest digest = MessageDigest.getInstance("SHA-256");

         byte[] hash = digest.digest(input.getBytes("UTF-8"));
         StringBuffer hexString = new StringBuffer();

         for (int i = 0; i < hash.length; i++) {
            String hex = Integer.toHexString(0xff & hash[i]);
            if (hex.length() == 1) {
               hexString.append('0');
            }

            hexString.append(hex);
         }
         return hexString.toString();

      } catch (NoSuchAlgorithmException e) {
         e.printStackTrace();
         throw new RuntimeException(e);

      } catch (UnsupportedEncodingException e) {
         e.printStackTrace();
         throw new RuntimeException(e);
      }
   }
}

3. Hash 계산로직 추가.

위 BcUtils 를 이용하여 Block 안 Hash값을 만드는 로직을 추가해보자.
Block 내 메소드 추가(소스코드)

/**
 * Hash값 계산하기!
 *
 * @return
 */
public String calculateHash() {
   return BcUtils.generateHash(previousHash, Long.toString(timeStamp), data);
}

생성자 내에 해당 메소드 호출 추가

/**
 * Block Constructor
 *
 * @param data
 * @param previousHash
 */
public Block(String data, String previousHash) {
   this.data = data;
   this.previousHash = previousHash;

   this.timeStamp = new Date().getTime();
   this.hash = calculateHash(); //추가!!
}

4. Genesis Block 호출하기!

첫번째 블럭 생성

Block genesisBlock = new Block("이건 Genesis Block 입니다.", "0");
System.out.println("Genesis Block Hash : " + genesisBlock.getHash());

메인 메소드를 만들어 호출하면 아래와 같은 결과를 얻을 수 있다.(호출할 때마다 Hash값이 달라진다.)

Genesis Block Hash : f57e2c72feba62234118d1356799c367a802c342156a43ac2774698bb316941e

몇개를 더 추가해서 출력해보면…. 아래와 같다.

Block genesisBlock = new Block("이건 Genesis Block 입니다.", "0");
System.out.println("Genesis Block Hash : " + genesisBlock.getHash());

Block secBlock = new Block("이건 두번째 블럭 입니다.", genesisBlock.getHash());
System.out.println("Second Block Hash : " + secBlock.getHash());

Block thirdBlock = new Block("이건 세번째 블럭 입니다.", secBlock.getHash());
System.out.println("Hash for block 3 : " + thirdBlock.getHash());

Genesis Block Hash : f57e2c72feba62234118d1356799c367a802c342156a43ac2774698bb316941e Second Block Hash : 082902f4d78eab658b964d9743532178073da2b9d529b00752fa5588034fb2a2 Hash for block 3 : 97a821109da7ed12fc3263452670d42b392d71772dd70b81720a23e1d898bf15

5. 블록체인 만들기.

간단하게 static List를 만들어서 블럭들을 생성해 보자.

/**
 * BlockChain 메인 클래스
 *
 * @author akageun
 */
public class BlockChain {

   public static List<Block> BLOCK_CHAIN = new LinkedList<>();

   public static void main(String[] args) {

      BLOCK_CHAIN.add(new Block("이건 Genesis Block 입니다.", "0"));
      BLOCK_CHAIN.add(new Block("이건 두번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));
      BLOCK_CHAIN.add(new Block("이건 세번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));

      for (Block block : BLOCK_CHAIN) {
         System.out.println("=========");

         System.out.println("hash : " + block.getHash());
         System.out.println("previousHash : " + block.getPreviousHash());
         System.out.println("timeStamp : " + block.getTimeStamp());
         System.out.println("Data : " + block.getData());
      }

      System.out.println("=========");
   }

}

결과 ```

=========

hash : 0f7e40c1f99be348a2a600f678ef6e64136d4ea6dc3d7457561e572129c628c9

previousHash : 0

timeStamp : 1532238023070

Data : 이건 Genesis Block 입니다.

=========

hash : b3a2226d4dafb77bfca41c2d792e7590df544e34450bfd5ecd69e71124f6baea

previousHash : 0f7e40c1f99be348a2a600f678ef6e64136d4ea6dc3d7457561e572129c628c9

timeStamp : 1532238023086

Data : 이건 두번째 블럭 입니다.

=========

hash : 57caa0507cbed37fbde89a4d80b2ea68450cff3698fba56856858093d8ac6982

previousHash : b3a2226d4dafb77bfca41c2d792e7590df544e34450bfd5ecd69e71124f6baea

timeStamp : 1532238023086

Data : 이건 세번째 블럭 입니다.

# 6. 무결성 검사
- 계산한 Hash값이 같은지, Block 내 PreviousBlock 과 실제 이전 블럭 Hash값이 같은지를 검증하는 로직
- 구현 소스

```java
/**
 * 블록 검증
 *
 *
 * @return
 */
private static boolean isValidBlockChain() {
   Block currentBlock;
   Block previousBlock;

   for (int i = 1; i < BLOCK_CHAIN.size(); i++) { //GenesisBlock 은 제외한다.
      currentBlock = BLOCK_CHAIN.get(i);
      previousBlock = BLOCK_CHAIN.get(i - 1);

      if (currentBlock.getHash().equals(currentBlock.calculateHash()) == false) { //만들어 놓은 Hash값과 계산한 Hash값이 같은지 검증!
         System.out.println("Not Equals Current Block Hash!!");
         return false;
      }

      if (currentBlock.getPreviousHash().equals(previousBlock.getHash()) == false) {
         System.out.println("Not Equals Previous Block Hash!!");
         return false;
      }

   }

   return true;
}

7. 채굴!(마이닝)

작업증명’(Proof-of-Work) : BlockChain의 Block Hash는 Difficulty에 따라 선택된 Target 데이터 규격을 만족해야 한다.
Block Class 수정( nonce 값 추가)

private int nonce;

/**
 * get nonce
 * 
 * @return
 */
public int getNonce() {
   return nonce;
}
  - Hash 값 연산하는 부분에 nonce 값 추가

/**
 * Hash값 계산하기!
 *
 * @return
 */
public String calculateHash() {
   return BcUtils.generateHash(previousHash, Long.toString(timeStamp), Integer.toString(nonce) , data);
}
  - 채굴 함수 추가

/**
 * Mining
 */
public void mineBlock() {
   char[] targetChar = new char[BlockChain.DIFFICULTY];
   Arrays.fill(targetChar, '0');
   String target = String.valueOf(targetChar);

   while (hash.substring(0, BlockChain.DIFFICULTY).equals(target) == false) {
      nonce++;
      hash = calculateHash();
   }

   System.out.println("Block Mined!!! : " + hash);
}

난이도 추가

public static int DIFFICULTY = 5;

무결성 검증 코드 내 로직 추가

if (currentBlock.getHash().substring(0, DIFFICULTY).equals(hashTarget) == false) {
   System.out.println("This block hasn't been mined");
   return false;
}

채굴해보기

BLOCK_CHAIN.add(new Block("이건 Genesis Block 입니다.", "0"));
BLOCK_CHAIN.get(0).mineBlock();

BLOCK_CHAIN.add(new Block("이건 두번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));
BLOCK_CHAIN.get(1).mineBlock();

BLOCK_CHAIN.add(new Block("이건 세번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));
BLOCK_CHAIN.get(2).mineBlock();

BLOCK_CHAIN.add(new Block("이건 네번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));
BLOCK_CHAIN.get(3).mineBlock();

결과

Block Mined!!! : 00000fdd8a35c69f5925051899635e1704af98bdd7da3504ed9bc36b5be30901

Block Mined!!! : 00000d8e9a9e735e8f7cbdae41458379ab8b4ac3de7826671eb10f2b7def35bd

Block Mined!!! : 000005dd4dc19710d82dda43d230ec6eabc8041af0fc0a489279802d172f8d41

Block Mined!!! : 000006ff67b1e5735d8891e3e389620f541aa3467e73471a4e2d7b11f841ed3a

=========

hash : 00000fdd8a35c69f5925051899635e1704af98bdd7da3504ed9bc36b5be30901

previousHash : 0

timeStamp : 1532240373740

Data : 이건 Genesis Block 입니다.

nonce : 465518

=========

hash : 00000d8e9a9e735e8f7cbdae41458379ab8b4ac3de7826671eb10f2b7def35bd

previousHash : 00000fdd8a35c69f5925051899635e1704af98bdd7da3504ed9bc36b5be30901

timeStamp : 1532240374917

Data : 이건 두번째 블럭 입니다.

nonce : 1603790

=========

hash : 000005dd4dc19710d82dda43d230ec6eabc8041af0fc0a489279802d172f8d41

previousHash : 00000d8e9a9e735e8f7cbdae41458379ab8b4ac3de7826671eb10f2b7def35bd

timeStamp : 1532240378568

Data : 이건 세번째 블럭 입니다.

nonce : 2130959

=========

hash : 000006ff67b1e5735d8891e3e389620f541aa3467e73471a4e2d7b11f841ed3a

previousHash : 000005dd4dc19710d82dda43d230ec6eabc8041af0fc0a489279802d172f8d41

timeStamp : 1532240383239

Data : 이건 네번째 블럭 입니다.

nonce : 504539

=========

This Blockchain is Valid : true

전체소스

1. Block 소스

package kr.geun.o.bc.basic;

import java.util.Arrays;
import java.util.Date;

/**
 * Block Class
 *
 * @author akageun
 */
public class Block {

   private String hash;
   private String previousHash;

   private String data;
   private long timeStamp;

   private int nonce;

   private Block() {

   }

   /**
    * Block Constructor
    *
    * @param data
    * @param previousHash
    */
   public Block(String data, String previousHash) {
      this.data = data;
      this.previousHash = previousHash;

      this.timeStamp = new Date().getTime();
      this.hash = calculateHash();
   }

   /**
    * Hash값 계산하기!
    *
    * @return
    */
   public String calculateHash() {
      return BcUtils.generateHash(previousHash, Long.toString(timeStamp), Integer.toString(nonce), data);
   }

   /**
    * Mining
    */
   public void mineBlock() {
      char[] targetChar = new char[BlockChain.DIFFICULTY];
      Arrays.fill(targetChar, '0');
      String target = String.valueOf(targetChar);

      while (hash.substring(0, BlockChain.DIFFICULTY).equals(target) == false) {
         nonce++;
         hash = calculateHash();
      }

      System.out.println("Block Mined!!! : " + hash);
   }

   /**
    * get previousHash
    *
    * @return
    */
   public String getPreviousHash() {
      return previousHash;
   }

   /**
    * get Hash
    *  - digital signature
    *
    * @return
    */
   public String getHash() {
      return hash;
   }

   /**
    * get TimeStamp
    *
    * @return
    */
   public long getTimeStamp() {
      return timeStamp;
   }

   /**
    * get Data
    *
    * @return
    */
   public String getData() {
      return data;
   }

   /**
    * get nonce
    *
    * @return
    */
   public int getNonce() {
      return nonce;
   }
}

2. BcUtils

package kr.geun.o.bc.basic;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * BlockChain Utils
 *
 * @author akageun
 */
public class BcUtils {

   /**
    * Hash 생성
    *
    * @param inputValues
    * @return
    */
   public static String generateHash(String... inputValues) {
      try {
         StringBuffer sb = new StringBuffer();
         for (String inputValue : inputValues) {
            sb.append(inputValue);
         }

         String input = sb.toString();

         MessageDigest digest = MessageDigest.getInstance("SHA-256");

         byte[] hash = digest.digest(input.getBytes("UTF-8"));
         StringBuffer hexString = new StringBuffer();

         for (int i = 0; i < hash.length; i++) {
            String hex = Integer.toHexString(0xff & hash[i]);
            if (hex.length() == 1) {
               hexString.append('0');
            }

            hexString.append(hex);
         }
         return hexString.toString();

      } catch (NoSuchAlgorithmException e) {
         e.printStackTrace();
         throw new RuntimeException(e);

      } catch (UnsupportedEncodingException e) {
         e.printStackTrace();
         throw new RuntimeException(e);
      }
   }
}

3. BlockChain

package kr.geun.o.bc.basic;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

/**
 * BlockChain 메인 클래스
 *
 * @author akageun
 */
public class BlockChain {

   public static List<Block> BLOCK_CHAIN = new LinkedList<>();

   public static int DIFFICULTY = 5;

   public static void main(String[] args) {

      BLOCK_CHAIN.add(new Block("이건 Genesis Block 입니다.", "0"));
      BLOCK_CHAIN.get(0).mineBlock();

      BLOCK_CHAIN.add(new Block("이건 두번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));
      BLOCK_CHAIN.get(1).mineBlock();

      BLOCK_CHAIN.add(new Block("이건 세번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));
      BLOCK_CHAIN.get(2).mineBlock();

      BLOCK_CHAIN.add(new Block("이건 네번째 블럭 입니다.", BLOCK_CHAIN.get(BLOCK_CHAIN.size() - 1).getHash()));
      BLOCK_CHAIN.get(3).mineBlock();

      for (Block block : BLOCK_CHAIN) {
         System.out.println("=========");

         System.out.println("hash : " + block.getHash());
         System.out.println("previousHash : " + block.getPreviousHash());
         System.out.println("timeStamp : " + block.getTimeStamp());
         System.out.println("Data : " + block.getData());
         System.out.println("nonce : " + block.getNonce());
      }

      System.out.println("=========");

      System.out.println("This Blockchain is Valid : " + isValidBlockChain());

   }

   /**
    * 블록 검증
    *
    *
    * @return
    */
   private static boolean isValidBlockChain() {
      Block currentBlock;
      Block previousBlock;

      char[] target = new char[BlockChain.DIFFICULTY];
      Arrays.fill(target, '0');

      String hashTarget = String.valueOf(target);

      for (int i = 1; i < BLOCK_CHAIN.size(); i++) { //GenesisBlock 은 제외한다.
         currentBlock = BLOCK_CHAIN.get(i);
         previousBlock = BLOCK_CHAIN.get(i - 1);

         if (currentBlock.getHash().equals(currentBlock.calculateHash()) == false) { //만들어 놓은 Hash값과 계산한 Hash값이 같은지 검증!
            System.out.println("Not Equals Current Block Hash!!");
            return false;
         }

         if (currentBlock.getPreviousHash().equals(previousBlock.getHash()) == false) {
            System.out.println("Not Equals Previous Block Hash!!");
            return false;
         }

         if (currentBlock.getHash().substring(0, DIFFICULTY).equals(hashTarget) == false) {
            System.out.println("This block hasn't been mined");
            return false;
         }

      }

      return true;
   }
}

참고 페이지

https://medium.com/programmers-blockchain/create-simple-blockchain-java-tutorial-from-scratch-6eeed3cb03fa
http://guruble.com/java-%EC%BD%94%EB%93%9C%EB%A1%9C-%EC%9D%B4%ED%95%B4%ED%95%98%EB%8A%94-%EB%B8%94%EB%A1%9D%EC%B2%B4%EC%9D%B8blockchain/

Java로 배워보는 BlockChain

1. Block 만들기

1) 소스코드

2. Hash(Digital Signature) 생성 메소드 만들기

3. Hash 계산로직 추가.

4. Genesis Block 호출하기!

5. 블록체인 만들기.

7. 채굴!(마이닝)

전체소스

1. Block 소스

2. BcUtils

3. BlockChain

참고 페이지

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