用Java 写段 RSA 加密算法

以下是使用Java实现RSA加密算法的示例代码：

import java.math.BigInteger;
import java.util.Random;

public class RSA {

    private BigInteger n, d, e;

    private int bitlen = 1024;

    public RSA() {
        Random r = new Random();
        BigInteger p = BigInteger.probablePrime(bitlen / 2, r);
        BigInteger q = BigInteger.probablePrime(bitlen / 2, r);
        n = p.multiply(q);
        BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));
        e = BigInteger.probablePrime(bitlen / 2, r);
        while (m.gcd(e).intValue() > 1) {
            e = BigInteger.probablePrime(bitlen / 2, r);
        }
        d = e.modInverse(m);
    }

    public RSA(BigInteger e, BigInteger d, BigInteger n) {
        this.e = e;
        this.d = d;
        this.n = n;
    }

    public synchronized BigInteger[] encrypt(byte[] message) {
        BigInteger[] cipher = new BigInteger[message.length];
        for (int i = 0; i < message.length; i++) {
            cipher[i] = BigInteger.valueOf(message[i]).modPow(e, n);
        }
        return cipher;
    }

    public synchronized byte[] decrypt(BigInteger[] cipher) {
        byte[] message = new byte[cipher.length];
        for (int i = 0; i < message.length; i++) {
            message[i] = cipher[i].modPow(d, n).byteValue();
        }
        return message;
    }

    public static void main(String[] args) {
        RSA rsa = new RSA();

        String text1 = "Hello World";
        System.out.println("Original Text 1: " + text1);

        //加密
        byte[] plaintext1 = text1.getBytes();
        BigInteger[] ciphertext1 = rsa.encrypt(plaintext1);
        System.out.print("Ciphertext 1: ");
        for (int i = 0; i < ciphertext1.length; i++) {
            System.out.print(ciphertext1[i].toString() + " ");
        }
        System.out.println();

        //解密
        byte[] decrypted1 = rsa.decrypt(ciphertext1);
        System.out.println("Decrypted Text 1: " + new String(decrypted1));

        String text2 = "RSA is an asymmetric cryptographic algorithm";
        System.out.println("Original Text 2: " + text2);

        //加密
        byte[] plaintext2 = text2.getBytes();
        BigInteger[] ciphertext2 = rsa.encrypt(plaintext2);
        System.out.print("Ciphertext 2: ");
        for (int i = 0; i < ciphertext2.length; i++) {
            System.out.print(ciphertext2[i].toString() + " ");
        }
        System.out.println();

        //解密
        byte[] decrypted2 = rsa.decrypt(ciphertext2);
        System.out.println("Decrypted Text 2: " + new String(decrypted2));
    }
}

上述代码实现了一个简单的RSA加密算法，包括密钥生成、加密和解密功能。在main函数中，我们加密了两个字符串并进行了解密。