用Java编写RSA加密算法

RSA加密算法是一种非对称加密算法，可以用于数据的加密和解密。下面是用Java语言实现RSA加密算法的代码示例：

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

public class RSA {

    private BigInteger n, d, e;

    private int bitlen = 1024;

    public RSA() {
        SecureRandom r = new SecureRandom();
        BigInteger p = new BigInteger(bitlen / 2, 100, r);
        BigInteger q = new BigInteger(bitlen / 2, 100, r);
        n = p.multiply(q);
        BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q
                .subtract(BigInteger.ONE));
        e = new BigInteger("3");
        while (m.gcd(e).intValue() > 1) {
            e = e.add(new BigInteger("2"));
        }
        d = e.modInverse(m);
    }

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

    public static void main(String[] args) {
        RSA rsa = new RSA();
        String text1 = "Hello World";
        System.out.println("Plaintext: " + text1);
        BigInteger plaintext = new BigInteger(text1.getBytes());
        BigInteger ciphertext = rsa.encrypt(plaintext);
        System.out.println("Ciphertext: " + ciphertext);
        BigInteger deciphertext = rsa.decrypt(ciphertext);
        System.out.println("Deciphertext: " + new String(deciphertext.toByteArray()));
    }

    public synchronized BigInteger encrypt(BigInteger message) {
        return message.modPow(e, n);
    }

    public synchronized BigInteger decrypt(BigInteger message) {
        return message.modPow(d, n);
    }
}

上述代码中，我们定义了一个RSA类，该类包含了RSA加密算法的实现。构造方法中，我们生成了一个1024位的RSA密钥对，其中包含了公钥e、私钥d以及模数n。encrypt()方法用于加密数据，decrypt()方法用于解密数据。我们还提供了一个简单的main()方法，用于测试加密和解密功能。