用Java模拟diffie-hellman算法

好的，下面是一个简单的Java代码实现Diffie-Hellman算法：

import java.math.BigInteger;
import java.security.SecureRandom;

public class DiffieHellman {
    private BigInteger p; //大质数
    private BigInteger g; //原根
    private BigInteger a; //私钥
    private BigInteger A; //公钥

    //构造函数
    public DiffieHellman(BigInteger p, BigInteger g) {
        this.p = p;
        this.g = g;
        this.a = new BigInteger(128, new SecureRandom()); //生成一个128位的随机数作为私钥
        this.A = g.modPow(a, p); //计算公钥
    }

    //计算共享秘密
    public BigInteger getSharedSecret(BigInteger B) {
        return B.modPow(a, p); //B的a次方模p
    }

    public BigInteger getP() {
        return p;
    }

    public BigInteger getG() {
        return g;
    }

    public BigInteger getA() {
        return a;
    }

    public BigInteger getA() {
        return A;
    }
}

使用方法如下：

public static void main(String[] args) {
    BigInteger p = new BigInteger("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1"
            + "29024E088A67CC74020BBEA63B139B22514A08798E3404DD"
            + "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245"
            + "E485B576625E7EC6F44C42E9A63A3620FFFFFFFFFFFFFFFF", 16); //大质数
    BigInteger g = BigInteger.valueOf(2); //原根

    DiffieHellman alice = new DiffieHellman(p, g); //Alice生成公钥、私钥
    DiffieHellman bob = new DiffieHellman(p, g); //Bob生成公钥、私钥

    BigInteger A = alice.getA(); //Alice将公钥A发送给Bob
    BigInteger B = bob.getA(); //Bob将公钥B发送给Alice

    BigInteger aliceSharedSecret = alice.getSharedSecret(B); //Alice计算共享秘密
    BigInteger bobSharedSecret = bob.getSharedSecret(A); //Bob计算共享秘密

    System.out.println("Alice's private key: " + alice.getA().toString(16));
    System.out.println("Bob's private key: " + bob.getA().toString(16));
    System.out.println("Alice's public key: " + A.toString(16));
    System.out.println("Bob's public key: " + B.toString(16));
    System.out.println("Alice's shared secret: " + aliceSharedSecret.toString(16));
    System.out.println("Bob's shared secret: " + bobSharedSecret.toString(16));
}

其中，`p`和`g`分别为大质数和原根，可以自行定义。在实际应用中，一般使用更大的质数和位数。Alice和Bob分别生成公钥和私钥，通过交换公钥来计算共享秘密。最后打印私钥、公钥和共享秘密。