接下來我們分析DH加密算法，一種適基于密鑰一致協議的加密算法。
DH
Diffie-Hellman算法(D-H算法)，密鑰一致協議。是由公開密鑰密碼體制的奠基人Diffie和Hellman所提出的一種思想。簡單的說就是允許兩名用戶在公開媒體上交換信息以生成"一致"的、可以共享的密鑰。換句話說，就是由甲方產出一對密鑰（公鑰、私鑰），乙方依照甲方公鑰產生乙方密鑰對（公鑰、私鑰）。以此為基線，作為數據傳輸保密基礎，同時雙方使用同一種對稱加密算法構建本地密鑰（SecretKey）對數據加密。這樣，在互通了本地密鑰（SecretKey）算法后，甲乙雙方公開自己的公鑰，使用對方的公鑰和剛才產生的私鑰加密數據，同時可以使用對方的公鑰和自己的私鑰對數據解密。不單單是甲乙雙方兩方，可以擴展為多方共享數據通訊，這樣就完成了網絡交互數據的安全通訊！該算法源于中國的同余定理——中國馀數定理。
流程分析：
1.甲方構建密鑰對兒，將公鑰公布給乙方，將私鑰保留；雙方約定數據加密算法；乙方通過甲方公鑰構建密鑰對兒，將公鑰公布給甲方，將私鑰保留。
2.甲方使用私鑰、乙方公鑰、約定數據加密算法構建本地密鑰，然后通過本地密鑰加密數據，發送給乙方加密后的數據；乙方使用私鑰、甲方公鑰、約定數據加密算法構建本地密鑰，然后通過本地密鑰對數據解密。
3.乙方使用私鑰、甲方公鑰、約定數據加密算法構建本地密鑰，然后通過本地密鑰加密數據，發送給甲方加密后的數據；甲方使用私鑰、乙方公鑰、約定數據加密算法構建本地密鑰，然后通過本地密鑰對數據解密。
通過java代碼實現如下：
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安全編碼組件
*
* @author 梁棟 http://www.bt285.cn http://www.5a520.cn
* @version 1.0
* @since 1.0
*/
public abstract class DHCoder extends Coder 
{
public static final String ALGORITHM = "DH";
/** *//**
* 默認密鑰字節數
*
* <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加密下需要一種對稱加密算法對數據加密，這里我們使用DES，也可以使用其他對稱加密算法。
*/
public static final String SECRET_ALGORITHM = "DES";
private static final String PUBLIC_KEY = "DHPublicKey";
private static final String PRIVATE_KEY = "DHPrivateKey";
/** *//**
* 初始化甲方密鑰
*
* @return
* @throws Exception
*/
public static Map<String, Object> initKey() throws Exception {
KeyPairGenerator keyPairGenerator = KeyPairGenerator
.getInstance(ALGORITHM);
keyPairGenerator.initialize(KEY_SIZE);
KeyPair keyPair = keyPairGenerator.generateKeyPair();
// 甲方公鑰
DHPublicKey publicKey = (DHPublicKey) keyPair.getPublic();
// 甲方私鑰
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;
}
/** *//**
* 初始化乙方密鑰
*
* @param key
* 甲方公鑰
* @return
* @throws Exception
*/
public static Map<String, Object> initKey(String key) throws Exception {
// 解析甲方公鑰
byte[] keyBytes = decryptBASE64(key);
X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);
// 由甲方公鑰構建乙方密鑰
DHParameterSpec dhParamSpec = ((DHPublicKey) pubKey).getParams();
KeyPairGenerator keyPairGenerator = KeyPairGenerator
.getInstance(keyFactory.getAlgorithm());
keyPairGenerator.initialize(dhParamSpec);
KeyPair keyPair = keyPairGenerator.generateKeyPair();
// 乙方公鑰
DHPublicKey publicKey = (DHPublicKey) keyPair.getPublic();
// 乙方私鑰
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
* 待加密數據
* @param publicKey
* 甲方公鑰
* @param privateKey
* 乙方私鑰
* @return
* @throws Exception
*/
public static byte[] encrypt(byte[] data, String publicKey,
String privateKey) throws Exception {
// 生成本地密鑰
SecretKey secretKey = getSecretKey(publicKey, privateKey);
// 數據加密
Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
cipher.init(Cipher.ENCRYPT_MODE, secretKey);
return cipher.doFinal(data);
}
/** *//**
* 解密<br>
*
* @param data
* 待解密數據
* @param publicKey
* 乙方公鑰
* @param privateKey
* 乙方私鑰
* @return
* @throws Exception
*/
public static byte[] decrypt(byte[] data, String publicKey,
String privateKey) throws Exception {
// 生成本地密鑰
SecretKey secretKey = getSecretKey(publicKey, privateKey);
// 數據解密
Cipher cipher = Cipher.getInstance(secretKey.getAlgorithm());
cipher.init(Cipher.DECRYPT_MODE, secretKey);
return cipher.doFinal(data);
}
/** *//**
* 構建密鑰
*
* @param publicKey
* 公鑰
* @param privateKey
* 私鑰
* @return
* @throws Exception
*/
private static SecretKey getSecretKey(String publicKey, String privateKey)
throws Exception {
// 初始化公鑰
byte[] pubKeyBytes = decryptBASE64(publicKey);
KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(pubKeyBytes);
PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);
// 初始化私鑰
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);
// 生成本地密鑰
SecretKey secretKey = keyAgree.generateSecret(SECRET_ALGORITHM);
return secretKey;
}
/** *//**
* 取得私鑰
*
* @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());
}
/** *//**
* 取得公鑰
*
* @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());
}
}
再給出一個測試類：
import static org.junit.Assert.*;
import java.util.Map;
import org.junit.Test;
/** *//**
*
* @author 梁棟 http://www.bt285.cn http://www.feng123.com
* @version 1.0
* @since 1.0
*/
public class DHCoderTest {
@Test
public void test() throws Exception {
// 生成甲方密鑰對兒
Map<String, Object> aKeyMap = DHCoder.initKey();
String aPublicKey = DHCoder.getPublicKey(aKeyMap);
String aPrivateKey = DHCoder.getPrivateKey(aKeyMap);
System.err.println("甲方公鑰:\r" + aPublicKey);
System.err.println("甲方私鑰:\r" + aPrivateKey);
// 由甲方公鑰產生本地密鑰對兒
Map<String, Object> bKeyMap = DHCoder.initKey(aPublicKey);
String bPublicKey = DHCoder.getPublicKey(bKeyMap);
String bPrivateKey = DHCoder.getPrivateKey(bKeyMap);
System.err.println("乙方公鑰:\r" + bPublicKey);
System.err.println("乙方私鑰:\r" + bPrivateKey);
String aInput = "abc ";
System.err.println("原文: " + aInput);
// 由甲方公鑰，乙方私鑰構建密文
byte[] aCode = DHCoder.encrypt(aInput.getBytes(), aPublicKey,
bPrivateKey);
// 由乙方公鑰，甲方私鑰解密
byte[] aDecode = DHCoder.decrypt(aCode, bPublicKey, aPrivateKey);
String aOutput = (new String(aDecode));
System.err.println("解密: " + aOutput);
assertEquals(aInput, aOutput);
System.err.println(" ===============反過來加密解密================== ");
String bInput = "def ";
System.err.println("原文: " + bInput);
// 由乙方公鑰，甲方私鑰構建密文
byte[] bCode = DHCoder.encrypt(bInput.getBytes(), bPublicKey,
aPrivateKey);
// 由甲方公鑰，乙方私鑰解密
byte[] bDecode = DHCoder.decrypt(bCode, aPublicKey, bPrivateKey);
String bOutput = (new String(bDecode));
System.err.println("解密: " + bOutput);
assertEquals(bInput, bOutput);
}
}
控制臺輸出：
- 甲方公鑰:
- MIHfMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYXrgHz
- W5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpDTWSG
- kx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgANDAAJAdAWBVmIzqcko
- Ej6qFjLDL2+Y3FPq1iRbnOyOpDj71yKaK1K+FhTv04B0zy4DKcvAASV7/Gv0W+bgqdmffRkqrQ==
-
- 甲方私鑰:
- MIHRAgEAMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYX
- rgHzW5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpD
- TWSGkx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgAQyAjACJRfy1LyR
- eHyD+4Hfb+xR0uoIGR1oL9i9Nk6g2AAuaDPgEVWHn+QXID13yL/uDos=
-
- 乙方公鑰:
- MIHfMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYXrgHz
- W5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpDTWSG
- kx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgANDAAJAVEYSfBA+I9nr
- dWw3OBv475C+eBrWBBYqt0m6/eu4ptuDQHwV4MmUtKAC2wc2nNrdb1wmBhY1X8RnWkJ1XmdDbQ==
-
- 乙方私鑰:
- MIHSAgEAMIGXBgkqhkiG9w0BAwEwgYkCQQD8poLOjhLKuibvzPcRDlJtsHiwXt7LzR60ogjzrhYX
- rgHzW5Gkfm32NBPF4S7QiZvNEyrNUNmRUb3EPuc3WS4XAkBnhHGyepz0TukaScUUfbGpqvJE8FpD
- TWSGkx0tFCcbnjUDC3H9c9oXkGmzLik1Yw4cIGI1TQ2iCmxBblC+eUykAgIBgAQzAjEAqaZiCdXp
- 2iNpdBlHRaO9ir70wo2n32xNlIzIX19VLSPCDdeUWkgRv4CEj/8k+/yd
-
- 原文: abc
- 解密: abc
- ===============反過來加密解密==================
- 原文: def
- 解密: def