用Java实现RSA加密和解密

RSA加密和解密的实现步骤如下：

1. 生成RSA密钥对

KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
keyPairGen.initialize(1024);
KeyPair keyPair = keyPairGen.generateKeyPair();

2. 获取公钥和私钥

PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();

3. 使用公钥加密

Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] cipherText = cipher.doFinal(plainText.getBytes());

4. 使用私钥解密

cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] decryptedText = cipher.doFinal(cipherText);

完整代码如下：

import javax.crypto.Cipher;
import java.security.*;

public class RSAUtil {

    /**
     * 生成RSA密钥对
     *
     * @return KeyPair
     * @throws NoSuchAlgorithmException
     */
    public static KeyPair generateKeyPair() throws NoSuchAlgorithmException {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
        keyPairGen.initialize(1024);
        return keyPairGen.generateKeyPair();
    }

    /**
     * 使用公钥加密
     *
     * @param plainText  明文
     * @param publicKey  公钥
     * @return byte[] 加密后的数据
     * @throws Exception
     */
    public static byte[] encrypt(String plainText, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(plainText.getBytes());
    }

    /**
     * 使用私钥解密
     *
     * @param cipherText 密文
     * @param privateKey 私钥
     * @return String 解密后的数据
     * @throws Exception
     */
    public static String decrypt(byte[] cipherText, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] decryptedText = cipher.doFinal(cipherText);
        return new String(decryptedText);
    }

    public static void main(String[] args) throws Exception {
        String plainText = "Hello World!";

        // 生成密钥对
        KeyPair keyPair = generateKeyPair();
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

        // 加密
        byte[] cipherText = encrypt(plainText, publicKey);

        // 解密
        String decryptedText = decrypt(cipherText, privateKey);

        System.out.println("明文: " + plainText);
        System.out.println("密文: " + new String(cipherText));
        System.out.println("解密后的明文: " + decryptedText);
    }
}