java实现diffie-hellman密钥交换

Diffie-Hellman密钥交换算法是一种公开密钥加密方法，其基本思想是通过在非安全通道上交换公共信息来协商出一个共享密钥，从而实现安全通信。

下面是Java实现Diffie-Hellman密钥交换的示例代码：

1. 生成密钥对

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;

public class DHKeyPairGenerator {
    public static void main(String[] args) throws NoSuchAlgorithmException {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("DH");
        keyPairGenerator.initialize(512); // 密钥长度为512位
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        System.out.println("私钥：" + keyPair.getPrivate());
        System.out.println("公钥：" + keyPair.getPublic());
    }
}

2. 密钥协商

import javax.crypto.KeyAgreement;
import java.security.*;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;

public class DHKeyAgreement {
    public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException, InvalidKeyException {
        // 甲方生成密钥对
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("DH");
        keyPairGenerator.initialize(512);
        KeyPair keyPairA = keyPairGenerator.generateKeyPair();
        System.out.println("甲方私钥：" + keyPairA.getPrivate());
        System.out.println("甲方公钥：" + keyPairA.getPublic());

        // 乙方生成密钥对
        KeyPair keyPairB = keyPairGenerator.generateKeyPair();
        System.out.println("乙方私钥：" + keyPairB.getPrivate());
        System.out.println("乙方公钥：" + keyPairB.getPublic());

        // 甲方将公钥发送给乙方
        byte[] publicKeyA = keyPairA.getPublic().getEncoded();
        // 乙方将公钥发送给甲方
        byte[] publicKeyB = keyPairB.getPublic().getEncoded();

        // 密钥协商
        KeyFactory keyFactory = KeyFactory.getInstance("DH");
        X509EncodedKeySpec keySpecA = new X509EncodedKeySpec(publicKeyA);
        PublicKey publicKeyA2 = keyFactory.generatePublic(keySpecA);
        X509EncodedKeySpec keySpecB = new X509EncodedKeySpec(publicKeyB);
        PublicKey publicKeyB2 = keyFactory.generatePublic(keySpecB);

        KeyAgreement keyAgreementA = KeyAgreement.getInstance("DH");
        keyAgreementA.init(keyPairA.getPrivate());
        keyAgreementA.doPhase(publicKeyB2, true);
        byte[] secretA = keyAgreementA.generateSecret();

        KeyAgreement keyAgreementB = KeyAgreement.getInstance("DH");
        keyAgreementB.init(keyPairB.getPrivate());
        keyAgreementB.doPhase(publicKeyA2, true);
        byte[] secretB = keyAgreementB.generateSecret();

        if (MessageDigest.isEqual(secretA, secretB)) {
            System.out.println("密钥协商成功！共享密钥：" + new String(secretA));
        } else {
            System.out.println("密钥协商失败！");
        }
    }
}

在以上示例代码中，我们首先生成了甲方和乙方的密钥对，然后将甲方的公钥发送给乙方，乙方也将自己的公钥发送给甲方。接下来，甲方和乙方分别依据对方的公钥计算出共享密钥，并进行比较，若相等则密钥协商成功。