RSA 私钥加密，公钥解密

```
public class RSATest {

public static void main(String[] args) throws Exception {
        // 生成公钥和私钥
        KeyPair keyPair = generateKeyPair();
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

// 要加密的信息
        String message = "This is a very long message that needs to be encrypted in chunks. It should be longer than a single RSA encryption block to demonstrate chunking.";

// 加密
        byte[] encryptedMessage = encrypt(message.getBytes(), privateKey);
		//byte[] encryptedMessage = encrypt(Base64.getDecoder().decode("XXX"), privateKey);

// 解密
        byte[] decryptedMessage = decrypt(encryptedMessage, publicKey);

// 输出结果
        System.out.println("Original message: " + message);
        System.out.println("Decrypted message: " + new String(decryptedMessage));

/* -----------  以下测试序列化 ----------*/

PublicKey publicKey2 = getPublicKey(convertPublic(publicKey));
        PrivateKey privateKey2 = getPrivateKey(convertPrivate(privateKey));
        // 加密
        byte[] encryptedMessage2 = encrypt(message.getBytes(), privateKey2);

String dataStr = Base64.getEncoder().encodeToString(encryptedMessage2);
        System.out.println("密文： " + dataStr);

// 解密
        byte[] decryptedMessage2 = decrypt(Base64.getDecoder().decode(dataStr), publicKey2);

System.out.println("Original message2: " + message);
        System.out.println("Decrypted message2: " + new String(decryptedMessage2));
    }

private static KeyPair generateKeyPair() throws Exception {
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(1024);
        return keyGen.generateKeyPair();
    }

private static byte[] encrypt(byte[] message, Key publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        int maxLength = 109;
        List<byte[]> chunks = new ArrayList<>();
        for (int i = 0; i < message.length; i += maxLength) {
            byte[] chunk = new byte[Math.min(maxLength, message.length - i)];
            System.arraycopy(message, i, chunk, 0, chunk.length);
            chunks.add(cipher.doFinal(chunk));
        }
        return combineChunks(chunks);
    }

private static byte[] decrypt(byte[] encryptedMessage, Key privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        int chunkSize = 128; // 对于1024位的密钥
        List<byte[]> chunks = new ArrayList<>();
        for (int i = 0; i < encryptedMessage.length; i += chunkSize) {
            byte[] chunk = new byte[chunkSize];
            System.arraycopy(encryptedMessage, i, chunk, 0, chunkSize);
            chunks.add(cipher.doFinal(chunk));
        }
        return combineChunks(chunks);
    }

private static byte[] combineChunks(List<byte[]> chunks) {
        int totalLength = chunks.stream().mapToInt(chunk -> chunk.length).sum();
        byte[] result = new byte[totalLength];
        int currentPosition = 0;
        for (byte[] chunk : chunks) {
            System.arraycopy(chunk, 0, result, currentPosition, chunk.length);
            currentPosition += chunk.length;
        }
        return result;
    }

public static String convertPublic(PublicKey publicKey) {
        return Base64.getEncoder()
                .withoutPadding()
                .encodeToString(publicKey.getEncoded());
    }

public static String convertPrivate(PrivateKey privateKey) {
        return Base64.getEncoder()
                .withoutPadding()
                .encodeToString(privateKey.getEncoded());
    }

@SneakyThrows
    public static PublicKey getPublicKey(String sshPublicKey) {
        sshPublicKey = sshPublicKey.replace("\n", "");
        byte[] publicKeyBytes = Base64.getDecoder().decode(sshPublicKey);
        // 创建X509EncodedKeySpec对象
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(publicKeyBytes);
        return KeyFactory.getInstance("RSA").generatePublic(keySpec);
    }

@SneakyThrows
    public static PrivateKey getPrivateKey(String sshPrivateKey) {
        sshPrivateKey = sshPrivateKey.replace("\n", "");
        byte[] byteKey = Base64.getDecoder().decode(sshPrivateKey);
        PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(byteKey);
        return KeyFactory.getInstance("RSA").generatePrivate(pkcs8EncodedKeySpec);
    }

}

```