Merge pull request #1 from comnics/dev-init

블록생성과 채굴

.classpath

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

.project

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>kbda-blockchain</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

src/org/kbda/blockchain/KbdaBlockchain.java

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+package org.kbda.blockchain;
+
+import org.kbda.bockchain.core.Block;
+
+public class KbdaBlockchain {
+
+	public static int difficulty = 5;
+
+	public static void main(String[] arg) {
+
+		//블럭을 만듭니다.
+		Block block = new Block("Genesis block", "0");
+		block.mineBlock(difficulty);
+
+	}
+
+}

src/org/kbda/blockchain/util/StringUtil.java

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+package org.kbda.blockchain.util;
+
+import java.security.Key;
+import java.security.MessageDigest;
+import java.security.PrivateKey;
+import java.security.PublicKey;
+import java.security.Signature;
+import java.util.Base64;
+
+public class StringUtil {
+	public static String applySha256(String input) {
+		try {
+			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 (Exception e) {
+			throw new RuntimeException(e);
+		}
+	}
+
+	// Applies ECDSA Signature and returns the result ( as bytes ).
+	public static byte[] applyECDSASig(PrivateKey privateKey, String input) {
+		Signature dsa;
+		byte[] output = new byte[0];
+		try {
+			dsa = Signature.getInstance("ECDSA", "BC");
+			dsa.initSign(privateKey);
+			byte[] strByte = input.getBytes();
+			dsa.update(strByte);
+			byte[] realSig = dsa.sign();
+			output = realSig;
+		} catch (Exception e) {
+			throw new RuntimeException(e);
+		}
+		return output;
+	}
+
+	// Verifies a String signature
+	public static boolean verifyECDSASig(PublicKey publicKey, String data, byte[] signature) {
+		try {
+			Signature ecdsaVerify = Signature.getInstance("ECDSA", "BC");
+			ecdsaVerify.initVerify(publicKey);
+			ecdsaVerify.update(data.getBytes());
+			return ecdsaVerify.verify(signature);
+		} catch (Exception e) {
+			throw new RuntimeException(e);
+		}
+	}
+
+	public static String getStringFromKey(Key key) {
+		return Base64.getEncoder().encodeToString(key.getEncoded());
+	}
+}

src/org/kbda/bockchain/core/Block.java

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+package org.kbda.bockchain.core;
+
+import java.util.Date;
+
+import org.kbda.blockchain.util.StringUtil;
+
+public class Block {
+
+	public String hash;			/* 해시값 */
+	public String previousHash;	/* 이전 블럭의 해시값 */
+	private String data; 		/* 블럭의 data */
+	private long timestamp; 	/* timestamp */
+
+	private int nonce;
+
+	/**
+	 * 새로운 블럭을 생성합니다.
+	 * 
+	 * @param data
+	 * @param previousHash
+	 */
+	public Block(String data, String previousHash ) {
+		this.data = data;
+		this.previousHash = previousHash;
+		this.timestamp = new Date().getTime();
+		this.hash = calculateHash();	//생성시 먼저 hash 값을 하나 만들어 넣어둡니다.
+	}
+
+	/**
+	 * 새로운 해시값을 생성합니다.
+	 * @return
+	 */
+	public String calculateHash() {
+		String calculatedhash = StringUtil.applySha256( 
+				previousHash +
+				Long.toString(timestamp) +
+				Integer.toString(nonce) + 
+				data 
+				);
+		return calculatedhash;
+	}
+
+	/**
+	 * 채굴합니다.
+	 * 
+	 * @param difficulty
+	 */
+	public void mineBlock(int difficulty) {
+		//간단한 테스트와 이해를 돕기위해 target을 difficulty 숫자 만큼 앞에 0으로 채웁니다.
+		String target = new String(new char[difficulty]).replace('\0', '0');
+
+		//생성된 hash가 target과 동일하면 채굴 성공입니다.
+		//ex) difficulty가 3이면 target은 000이 되고, 생성된 hash가 000으로 시작하는 값이면 채굴 성공입니다.
+		//  채굴된 모든 hash가 000으로 시작하겠죠...ㅋㅋ
+		while(!hash.substring( 0, difficulty).equals(target)) {
+			nonce ++;
+			hash = calculateHash();
+
+			System.out.printf("\nGEN Hash #%d : %s", nonce, hash);
+		}
+		System.out.println("\n채굴 성공!!! : " + hash);
+	}
+}