Java加密技术（五）——非对称加密算法的由来DH

本文转载于http://snowolf.iteye.com/blog/382422

接下来我们分析DH加密算法，一种适基于密钥一致协议的加密算法。

DH

Diffie-Hellman算法(D-H算法)，密钥一致协议。是由公开密钥密码体制的奠基人Diffie和Hellman所提出的一种思想。简单的说就是允许两名用户在公开媒体上交换信息以生成"一致"的、可以共享的密钥。换句话说，就是由甲方产出一对密钥（公钥、私钥），乙方依照甲方公钥产生乙方密钥对（公钥、私钥）。以此为基线，作为数据传输保密基础，同时双方使用同一种对称加密算法构建本地密钥（SecretKey）对数据加密。这样，在互通了本地密钥（SecretKey）算法后，甲乙双方公开自己的公钥，使用对方的公钥和刚才产生的私钥加密数据，同时可以使用对方的公钥和自己的私钥对数据解密。不单单是甲乙双方两方，可以扩展为多方共享数据通讯，这样就完成了网络交互数据的安全通讯！该算法源于中国的同余定理——中国馀数定理。



流程分析：

1.甲方构建密钥对儿，将公钥公布给乙方，将私钥保留；双方约定数据加密算法；乙方通过甲方公钥构建密钥对儿，将公钥公布给甲方，将私钥保留。

2.甲方使用私钥、乙方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥加密数据，发送给乙方加密后的数据；乙方使用私钥、甲方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥对数据解密。

3.乙方使用私钥、甲方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥加密数据，发送给甲方加密后的数据；甲方使用私钥、乙方公钥、约定数据加密算法构建本地密钥，然后通过本地密钥对数据解密。







通过java代码实现如下：Coder类见
Java加密技术（一）

Java代码


import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;
import javax.crypto.KeyAgreement;
import javax.crypto.SecretKey;
import javax.crypto.interfaces.DHPrivateKey;
import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;

/**
* DH安全编码组件
*
* @author 梁栋
* @version 1.0
* @since 1.0
*/
public abstract class DHCoder extends Coder {
public static final String ALGORITHM = "DH";

/**
* 默认密钥字节数
*
* <pre>
* DH
* Default Keysize 1024
* Keysize must be a multiple of 64, ranging from 512 to 1024 (inclusive).
* </pre>
*/
private static final int KEY_SIZE = 1024;

/**
* DH加密下需要一种对称加密算法对数据加密，这里我们使用DES，也可以使用其他对称加密算法。
*/
public static final String SECRET_ALGORITHM = "DES";
private static final String PUBLIC_KEY = "DHPublicKey";
private static final String PRIVATE_KEY = "DHPrivateKey";

/**
* 初始化甲方密钥
*
* @return
* @throws Exception
*/
public static Map<String, Object> initKey() throws Exception {
KeyPairGenerator keyPairGenerator = KeyPairGenerator
.getInstance(ALGORITHM);
keyPairGenerator.initialize(KEY_SIZE);

KeyPair keyPair = keyPairGenerator.generateKeyPair();

// 甲方公钥
DHPublicKey publicKey = (DHPublicKey) keyPair.getPublic();

// 甲方私钥
DHPrivateKey privateKey = (DHPrivateKey) keyPair.getPrivate();

Map<String, Object> keyMap = new HashMap<String, Object>(2);

keyMap.put(PUBLIC_KEY, publicKey);
keyMap.put(PRIVATE_KEY, privateKey);
return keyMap;
}

/**
* 初始化乙方密钥
*
* @param key
* 甲方公钥
* @return
* @throws Exception
*/
public static Map<String, Object> initKey(String key) throws Exception {
// 解析甲方公钥
byte[] keyBytes = decryptBASE64(key);
X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);

// 由甲方公钥构建乙方密钥
DHParameterSpec dhParamSpec = ((DHPublicKey) pubKey).getParams();

KeyPairGenerator keyPairGenerator = KeyPairGenerator
.getInstance(keyFactory.getAlgorithm());
keyPairGenerator.initialize(dhParamSpec);

KeyPair keyPair = keyPairGenerator.generateKeyPair();

// 乙方公钥
DHPublicKey publicKey = (DHPublicKey) keyPair.getPublic();

// 乙方私钥
DHPrivateKey privateKey = (DHPrivateKey) keyPair.getPrivate();

Map<String, Object> keyMap = new HashMap<String, Object>(2);

keyMap.put(PUBLIC_KEY, publicKey);
keyMap.put(PRIVATE_KEY, privateKey);

return keyMap;
}

/**
* 加密<br>
*
* @param data
* 待加密数据
* @param publicKey
* 甲方公钥
* @param privateKey
* 乙方私钥
* @return
* @throws Exception
*/
public static byte[] encrypt(byte[] data, String publicKey,
String privateKey) throws Exception {

// 生成本地密钥
SecretKey secretKey = getSecretKey(publicKey, privateKey);

// 数据加密
Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
cipher.init(Cipher.ENCRYPT_MODE, secretKey);

return cipher.doFinal(data);
}

/**
* 解密<br>
*
* @param data
* 待解密数据
* @param publicKey
* 乙方公钥
* @param privateKey
* 乙方私钥
* @return
* @throws Exception
*/
public static byte[] decrypt(byte[] data, String publicKey,
String privateKey) throws Exception {

// 生成本地密钥
SecretKey secretKey = getSecretKey(publicKey, privateKey);
// 数据解密
Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
cipher.init(Cipher.DECRYPT_MODE, secretKey);

return cipher.doFinal(data);
}

/**
* 构建密钥
*
* @param publicKey
* 公钥
* @param privateKey
* 私钥
* @return
* @throws Exception
*/
private static SecretKey getSecretKey(String publicKey, String privateKey)
throws Exception {
// 初始化公钥
byte[] pubKeyBytes = decryptBASE64(publicKey);

KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(pubKeyBytes);
PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);

// 初始化私钥
byte[] priKeyBytes = decryptBASE64(privateKey);

PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(priKeyBytes);
Key priKey = keyFactory.generatePrivate(pkcs8KeySpec);

KeyAgreement keyAgree = KeyAgreement.getInstance(keyFactory
.getAlgorithm());
keyAgree.init(priKey);
keyAgree.doPhase(pubKey, true);

// 生成本地密钥
SecretKey secretKey = keyAgree.generateSecret(SECRET_ALGORITHM);

return secretKey;
}

/**
* 取得私钥
*
* @param keyMap
* @return
* @throws Exception
*/
public static String getPrivateKey(Map<String, Object> keyMap)
throws Exception {
Key key = (Key) keyMap.get(PRIVATE_KEY);

return encryptBASE64(key.getEncoded());
}

/**
* 取得公钥
*
* @param keyMap
* @return
* @throws Exception
*/
public static String getPublicKey(Map<String, Object> keyMap)
throws Exception {
Key key = (Key) keyMap.get(PUBLIC_KEY);

return encryptBASE64(key.getEncoded());
}
}

再给出一个测试类：

Java代码


import static org.junit.Assert.*;

import java.util.Map;

import org.junit.Test;

/**
*
* @author 梁栋
* @version 1.0
* @since 1.0
*/
public class DHCoderTest {

@Test
public void test() throws Exception {
// 生成甲方密钥对儿
Map<String, Object> aKeyMap = DHCoder.initKey();
String aPublicKey = DHCoder.getPublicKey(aKeyMap);
String aPrivateKey = DHCoder.getPrivateKey(aKeyMap);

System.err.println("甲方公钥:\r" + aPublicKey);
System.err.println("甲方私钥:\r" + aPrivateKey);

// 由甲方公钥产生本地密钥对儿
Map<String, Object> bKeyMap = DHCoder.initKey(aPublicKey);
String bPublicKey = DHCoder.getPublicKey(bKeyMap);
String bPrivateKey = DHCoder.getPrivateKey(bKeyMap);

System.err.println("乙方公钥:\r" + bPublicKey);
System.err.println("乙方私钥:\r" + bPrivateKey);

String aInput = "abc ";
System.err.println("原文: " + aInput);

// 由甲方公钥，乙方私钥构建密文
byte[] aCode = DHCoder.encrypt(aInput.getBytes(), aPublicKey,
bPrivateKey);

// 由乙方公钥，甲方私钥解密
byte[] aDecode = DHCoder.decrypt(aCode, bPublicKey, aPrivateKey);
String aOutput = (new String(aDecode));

System.err.println("解密: " + aOutput);

assertEquals(aInput, aOutput);

System.err.println(" ===============反过来加密解密================== ");
String bInput = "def ";
System.err.println("原文: " + bInput);

// 由乙方公钥，甲方私钥构建密文
byte[] bCode = DHCoder.encrypt(bInput.getBytes(), bPublicKey,
aPrivateKey);

// 由甲方公钥，乙方私钥解密
byte[] bDecode = DHCoder.decrypt(bCode, aPublicKey, bPrivateKey);
String bOutput = (new String(bDecode));

System.err.println("解密: " + bOutput);

assertEquals(bInput, bOutput);
}

}

控制台输出：

Console代码


甲方公钥:
MIHfMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYXrgHz
W5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpDTWSG
kx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgANDAAJAdAWBVmIzqcko
Ej6qFjLDL2+Y3FPq1iRbnOyOpDj71yKaK1K+FhTv04B0zy4DKcvAASV7/Gv0W+bgqdmffRkqrQ==

甲方私钥:
MIHRAgEAMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYX
rgHzW5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpD
TWSGkx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgAQyAjACJRfy1LyR
eHyD+4Hfb+xR0uoIGR1oL9i9Nk6g2AAuaDPgEVWHn+QXID13yL/uDos=

乙方公钥:
MIHfMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYXrgHz
W5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpDTWSG
kx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgANDAAJ***EYSfBA+I9nr
dWw3OBv475C+eBrWBBYqt0m6/eu4ptuDQHwV4MmUtKAC2wc2nNrdb1wmBhY1X8RnWkJ1XmdDbQ==

乙方私钥:
MIHSAgEAMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYX
rgHzW5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpD
TWSGkx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgAQzAjEAqaZiCdXp
2iNpdBlHRaO9ir70wo2n32xNlIzIX19VLSPCDdeUWkgRv4CEj/8k+/yd

原文: abc
解密: abc
===============反过来加密解密==================
原文: def
解密: def

如我所言，甲乙双方在获得对方公钥后可以对发送给对方的数据加密，同时也能对接收到的数据解密，达到了数据安全通信的目的！