非对称加密算法 JAVA实现 ：DH

【密钥交换（DH）】

双方在没有确定共同密钥的情况下，生成密钥，不提供加密工作，加解密还需要其他对称加密算法实现

DH算法示例

import javax.crypto.KeyAgreement;
import javax.crypto.interfaces.DHPrivateKey;
import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;
import java.security.*;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

//1 生成源密钥
//2 把源公钥交给目标，目标通过源公钥，生成目标公钥和私钥
//3 把目标公钥交给源
//4 双方使用对方的公钥和和自己的私钥，生成本地密钥
//5 如果双方生成本地密钥相同则完成密钥交换
public class DHUtil {

  public static final String PUBLIC_KEY = "DH_Public_Key";
  public static final String PRIVATE_KEY = "DH_Private_key";

  /**
   * 生成源密钥对
   * @return
   * @throws Exception
   */
  public static Map<String,Object> initSourceKey() throws Exception{
    //创建KeyPairGenerator的实例，选用DH算法
    KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("DH");

    //初始化密钥长度，默认1024，可选范围512-65536 & 64的倍数
    keyPairGenerator.initialize(1024);

    //生成密钥对
    KeyPair keyPair = keyPairGenerator.generateKeyPair();
    DHPublicKey dhPublicKey = (DHPublicKey) keyPair.getPublic();
    DHPrivateKey dhPrivateKey = (DHPrivateKey) keyPair.getPrivate();

    //将密钥对放入Map
    Map<String,Object> keyMap = new HashMap<String, Object>();
    keyMap.put(PUBLIC_KEY, dhPublicKey);
    keyMap.put(PRIVATE_KEY, dhPrivateKey);
    return keyMap;
  }

  /**
   * 通过源公钥 生成 目标密钥对
   * @param sourcePublicKey
   * @return
   * @throws Exception
   */
  public static Map<String,Object> initTargetKey(byte[] sourcePublicKey) throws Exception {

    KeyFactory keyFactory = KeyFactory.getInstance("DH");

    //通过源公钥，生成keySpec，使用KeyFactory生成源PublicKey相关信息
    X509EncodedKeySpec keySpec = new X509EncodedKeySpec(sourcePublicKey);
    DHPublicKey sourcePublic = (DHPublicKey) keyFactory.generatePublic(keySpec);

    DHParameterSpec dhPublicKeyParams = sourcePublic.getParams();

    KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("DH");
    keyPairGenerator.initialize(dhPublicKeyParams);

    KeyPair keyPair = keyPairGenerator.generateKeyPair();
    DHPublicKey dhPublicKey = (DHPublicKey) keyPair.getPublic();
    DHPrivateKey dhPrivateKey = (DHPrivateKey) keyPair.getPrivate();

    //将密钥对放入Map
    Map<String,Object> keyMap = new HashMap<String, Object>();
    keyMap.put(PUBLIC_KEY, dhPublicKey);
    keyMap.put(PRIVATE_KEY, dhPrivateKey);
    return keyMap;
  }

  /**
   * 使用一方的公钥和另一方的私钥，生成本地密钥
   * @return
   */
  public static byte[] generateLocalSecretKey(byte[] aPublicKey, byte[] bPrivateKey) throws Exception{
    KeyFactory keyFactory = KeyFactory.getInstance("DH");

    //通过A公钥，生成keySpec，使用KeyFactory生成A PublicKey相关信息
    X509EncodedKeySpec keySpec = new X509EncodedKeySpec(aPublicKey);
    PublicKey publicKey = keyFactory.generatePublic(keySpec);

    //通过B私钥，生成B PrivateKey相关信息
    PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(bPrivateKey);
    PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);

    //通过KeyAgreement对A的PublicKey和B的PrivateKey进行加密
    KeyAgreement keyAgreement = KeyAgreement.getInstance("DH");
    keyAgreement.init(privateKey);
    keyAgreement.doPhase(publicKey,true);


    return keyAgreement.generateSecret("AES").getEncoded();//算法使用对称加密算法（DES，DESede，AES）
    //return keyAgreement.generateSecret();        // 也可以不选择算法，使用默认方法计算
  }

  //获取公钥字节数组
  public static byte[] getPublicKey(Map<String,Object> map){
    return ((DHPublicKey) map.get(PUBLIC_KEY)).getEncoded();
  }

  //获取私钥字节数组
  public static byte[] getPrivateKey(Map<String,Object> map){
    return ((DHPrivateKey) map.get(PRIVATE_KEY)).getEncoded();
  }

  public static void main(String[] args) throws Exception {

    byte[] source_public_key;
    byte[] source_private_key;
    byte[] source_local_key;

    byte[] target_public_key;
    byte[] target_private_key;
    byte[] target_local_key;

    Map<String, Object> sourceKey = initSourceKey();
    source_public_key = getPublicKey(sourceKey);
    source_private_key = getPrivateKey(sourceKey);

    System.out.println("源公钥："+BytesToHex.fromBytesToHex(source_public_key));
    System.out.println("源私钥："+BytesToHex.fromBytesToHex(source_private_key));

    Map<String, Object> targetKey = initTargetKey(getPublicKey(sourceKey));
    target_public_key = getPublicKey(targetKey);
    target_private_key = getPrivateKey(targetKey);

    System.out.println("目标公钥："+BytesToHex.fromBytesToHex(target_public_key));
    System.out.println("目标私钥："+BytesToHex.fromBytesToHex(target_private_key));

    source_local_key = generateLocalSecretKey(target_public_key, source_private_key);
    target_local_key = generateLocalSecretKey(source_public_key, target_private_key);

    System.out.println("源本地密钥："+BytesToHex.fromBytesToHex(source_local_key));
    System.out.println("目标本地密钥："+BytesToHex.fromBytesToHex(target_local_key));
  }
}