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需要考虑哪些问题？

在进行报文传输时，有两个问题需要考虑：

1. 消息防篡改
2. 加密报文

定义消息结构

为了方便后面使用，这里定义消息结构：

public static class Message {public String data; //消息public String sign; //签名public Message(String data, String sign) {this.data = data;this.sign = sign;}
}

对报文进行签名

首先我们假设消息是一个字符串：String msg = "Hello, message encryption!"

然后我们对这个报文计算摘要：byte[] msgHash = md5(msg)。只要两个字符串计算出的摘要相同，我们认为这两个字符串是相等的（即没有被篡改过）。

然而如果直接传输 msg 及其摘要，那么很容易被别人篡改，这时就需要对摘要进行加密，也就是所谓的签名。也就是防止篡改的核心。下面给出一个完整的实现：

这里只放主要流程，辅助方法见附录：

// 生成RSA密钥对
KeyPair keyPair = generateKeyPair();// 获取公钥和私钥
PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();// 要加密的原始数据
String originalMessage = "Hello, message encryption!";//发送端签名
Message message = sign(originalMessage, privateKey);
System.out.println("加密后的消息签名: " + message.sign);//接收端校验签名
boolean checkResult = checkSign(message, publicKey);
System.out.println("合法：" + checkResult);

对报文进行加密

在发送端： 首先生成 AES 密钥，使用AES对报文进行加密，然后使用 RSA 对 AES 密钥进行加密。（考虑到报文本身可能较大，而非对称RSA加密效率较差）

在接收端：使用 RSA解密 AES 密钥，使用解密的 AES 密钥解密报文。

// 生成RSA密钥对
KeyPair keyPair = generateKeyPair();// 获取公钥和私钥
PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();//生成 aes 密钥
byte[] aesKey = generateAesKey();
//使用公钥对 aes 密钥进行加密
byte[] encryptedAesKey = encrypt(aesKey, publicKey);//报文
String originalMessage = "Hello, message encryption!";// 使用AES密钥加密报文
byte[] encryptedMessage = encryptWithAes(originalMessage.getBytes(), aesKey);//将encryptedAesKey和encryptedMessage传给接收端
// 使用私钥解密AES密钥
byte[] decryptedAesKey = decrypt(encryptedAesKey, privateKey);// 使用AES密钥解密消息
String decryptedMessage = new String(decryptWithAes(encryptedMessage, decryptedAesKey));

附录

//公钥签名
public static Message sign(String originalMessage, PublicKey publicKey) throws Exception {byte[] bytes = calculateMD5(originalMessage);byte[] encryptedHash = encrypt(bytes, publicKey);String signStr = bytesToHex(encryptedHash);return new Message(originalMessage, signStr);
}//私钥签名
public static Message sign(String originalMessage, PrivateKey privateKey) throws Exception {byte[] bytes = calculateMD5(originalMessage);byte[] encryptedHash = encrypt(bytes, privateKey);String signStr = bytesToHex(encryptedHash);return new Message(originalMessage, signStr);
}//公钥验签
public static boolean checkSign(Message message, PublicKey publicKey) throws Exception {byte[] sign = hexToBytes(message.sign);byte[] md5Hash = decrypt(sign, publicKey);byte[] calcMd5Hash = calculateMD5(message.data);return Arrays.equals(md5Hash, calcMd5Hash);
}//私钥验签
public static boolean checkSign(Message message, PrivateKey privateKey) throws Exception {byte[] sign = hexToBytes(message.sign);byte[] md5Hash = decrypt(sign, privateKey);byte[] calcMd5Hash = calculateMD5(message.data);return Arrays.equals(md5Hash, calcMd5Hash);
}// 生成RSA密钥对
public static KeyPair generateKeyPair() throws Exception {KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");SecureRandom secureRandom = new SecureRandom();keyPairGenerator.initialize(2048, secureRandom);return keyPairGenerator.generateKeyPair();
}// 计算MD5哈希值
public static byte[] calculateMD5(String message) throws Exception {MessageDigest md = MessageDigest.getInstance("MD5");md.update(message.getBytes());return md.digest();
}// 使用公钥加密数据
public static byte[] encrypt(byte[] data, PublicKey publicKey) throws Exception {Cipher cipher = Cipher.getInstance("RSA");cipher.init(Cipher.ENCRYPT_MODE, publicKey);return cipher.doFinal(data);
}// 使用私钥加密数据
public static byte[] encrypt(byte[] data, PrivateKey privateKey) throws Exception {Cipher cipher = Cipher.getInstance("RSA");cipher.init(Cipher.ENCRYPT_MODE, privateKey);return cipher.doFinal(data);
}// 使用公钥解密数据
public static byte[] decrypt(byte[] data, PublicKey publicKey) throws Exception {Cipher cipher = Cipher.getInstance("RSA");cipher.init(Cipher.DECRYPT_MODE, publicKey);return cipher.doFinal(data);
}// 使用私钥解密数据
public static byte[] decrypt(byte[] data, PrivateKey privateKey) throws Exception {Cipher cipher = Cipher.getInstance("RSA");cipher.init(Cipher.DECRYPT_MODE, privateKey);return cipher.doFinal(data);
}// 生成AES密钥
public static byte[] generateAesKey() throws Exception {SecureRandom secureRandom = new SecureRandom();byte[] key = new byte[16];secureRandom.nextBytes(key);return key;
}// 使用AES密钥加密数据
public static byte[] encryptWithAes(byte[] data, byte[] key) throws Exception {Cipher cipher = Cipher.getInstance("AES");cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "AES"));return cipher.doFinal(data);
}// 使用AES密钥解密数据
public static byte[] decryptWithAes(byte[] encryptedData, byte[] key) throws Exception {Cipher cipher = Cipher.getInstance("AES");cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"));return cipher.doFinal(encryptedData);
}// 将字节数组转换为十六进制字符串
public static String bytesToHex(byte[] bytes) {StringBuilder hexString = new StringBuilder();for (byte b : bytes) {String hex = Integer.toHexString(0xff & b);if (hex.length() == 1) {hexString.append('0');}hexString.append(hex);}return hexString.toString();
}public static byte[] hexToBytes(String hex) {int len = hex.length();byte[] data = new byte[len / 2];for (int i = 0; i < len; i += 2) {data[i / 2] = (byte) ((Character.digit(hex.charAt(i), 16) << 4)+ Character.digit(hex.charAt(i + 1), 16));}return data;
}