发送方和接收方消息字节内容大小不匹配和 javax.crypto.AEADBadTagException：AES-GCM 模式下的标签不匹配答案

【问题标题】：Sender and Receiver Message bytes content size mismatch and javax.crypto.AEADBadTagException: Tag mismatch in AES-GCM mode发送方和接收方消息字节内容大小不匹配和 javax.crypto.AEADBadTagException：AES-GCM 模式下的标签不匹配
【发布时间】：2018-02-08 07:05:56
【问题描述】：

我使用了来自在线的示例 AES-GCM 示例 java 代码。UDP 客户端必须使用 AES-GCM 模式加密数据并发送到服务器。UDP 服务器必须接收和解密它。我这样做时有两个问题

1.我向服务器发送了“hi”消息（明文为2字节，加密后为18字节）。之后，服务器收到消息我们执行以下操作

DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
byte[] rec=receivePacket.getData();
String receivedData = new String(rec,0,receivePacket.getLength());
System.out.println(receivePacket.getLength());//18 bytes
System.out.println(receivedData.length);// 30 bytes(how???)

为什么两个大小不一样？？？

2.那么，当尝试解密 30 字节数据时（？），下面一行出现异常

byte[] plainText = cipher.doFinal(cipherText);

示例客户端：

class GCMClient
{
    // AES-GCM parameters
    public static final int AES_KEY_SIZE = 128; // in bits
    public static final int GCM_NONCE_LENGTH = 12; // in bytes
    public static final int GCM_TAG_LENGTH = 16; // in bytes
    public static void main(String args[]) throws Exception{        
        DatagramSocket clientSocket = new DatagramSocket();
        InetAddress IPAddress = InetAddress.getByName("192.168.1.8");
        byte[] sendData = new byte[1024];
        byte[] receiveData = new byte[1024];        
        byte[] input = "hi".getBytes(); //2 bytes 

        byte[] keyBytes ="qwertyuiopasdfgh".getBytes();
        SecretKey key = new SecretKeySpec(keyBytes, 0, keyBytes.length, "AES");       
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "SunJCE");
        byte[] nonce = new byte[GCM_NONCE_LENGTH];
        nonce = "poiuytrewqlk".getBytes();;;        
        GCMParameterSpec spec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, nonce);
        cipher.init(Cipher.ENCRYPT_MODE, key, spec);
        byte[] aad =  "Whatever I like".getBytes();;
        cipher.updateAAD(aad);
        byte[] cipherText = cipher.doFinal(input); 
        System.out.println(cipherText.length+ "data sent!!!!!!! "); //18 bytes after encryption
        DatagramPacket sendPacket = new DatagramPacket(cipherText, cipherText.length, IPAddress, 9999);
        clientSocket.send(sendPacket);  
        clientSocket.close();     
   }
}

示例服务器：

class GCMServer
{
     // AES-GCM parameters
    public static final int AES_KEY_SIZE = 128; // in bits
    public static final int GCM_NONCE_LENGTH = 12; // in bytes
    public static final int GCM_TAG_LENGTH = 16; // in bytes

    public static void main(String args[]) throws Exception{ 
        try{
            DatagramSocket serverSocket = new DatagramSocket(9999,InetAddress.getByName("192.168.1.8"));
            byte[] receiveData = new byte[1024];
            byte[] sendData = new byte[1024];
            while(true){           
                DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
                receivePacket.setData(new byte[4096]);  
                serverSocket.receive(receivePacket);
                byte[] rec=receivePacket.getData();
                String receivedData = new String(rec,0,receivePacket.getLength());          
                byte[] cipherText = receivedData.getBytes();

                System.out.println("received packet size before convert to bytes "+receivePacket.getLength());//it displays 18
                System.out.println("received packet size after convert to bytes "+cipherText.length);//it display 30 how???? it must be 18          


                byte[] keyBytes ="qwertyuiopasdfgh".getBytes();
                SecretKey key = new SecretKeySpec(keyBytes, 0, keyBytes.length, "AES");       
                Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "SunJCE");
                byte[] nonce = new byte[GCM_NONCE_LENGTH];
                nonce = "poiuytrewqlk".getBytes();;;        
                GCMParameterSpec spec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, nonce);            
                byte[] aad = "Whatever I like".getBytes();;         
                cipher.init(Cipher.DECRYPT_MODE, key, spec);     
                cipher.updateAAD(aad);      
                byte[] plainText = cipher.doFinal(cipherText);      
                System.out.println("After decryption "+new String(plainText));
            }
        }catch(Exception e){
            System.out.println("Exception caught "+e);//got Exception caught javax.crypto.AEADBadTagException: Tag mismatch!
        }
     }
}

【问题讨论】：

标签： java aes-gcm

【解决方案1】：

我不知道为什么字节内容大小不同。但是，当我使用以下代码时它解决了

 DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
    serverSocket.receive(receivePacket);
    byte[] rec=receivePacket.getData();
    byte[] cipherText=new byte[receivePacket.getLength()];
    System.arraycopy(rec, 0, cipherText, 0, receivePacket.getLength());

改为

DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
byte[] rec=receivePacket.getData();
String receivedData = new String(rec,0,receivePacket.getLength());

并解决了 javax.crypto.AEADBadTagException: Tag mismatch 异常

【讨论】：