解密TLS 1.2 AES-GCM数据包

Question

我正在开发一个Java程序来解密使用密码的TLS 1.2 Session TLS_RSA_WITH_AES_128_GCM_SHA256.我使用wireshark录制了一个测试会话.该主密钥是已知的.

No.     Time           Protocol Length Info
      4 0.000124000    TLSv1.2  166    Client Hello
      6 0.000202000    TLSv1.2  1074   Server Hello, Certificate, Server Hello Done
      8 0.001071000    TLSv1.2  393    Client Key Exchange, Change Cipher Spec, Finished
      9 0.003714000    TLSv1.2  301    New Session Ticket, Change Cipher Spec, Finished
     11 6.443056000    TLSv1.2  116    Application Data
     12 6.443245000    TLSv1.2  765    Application Data
     15 6.443390000    TLSv1.2  103    Alert (Level: Warning, Description: Close Notify)

Packet 11包含HTTP GET Request 我正在尝试解密的内容.

握手数据:

Cipher:        TLS_RSA_WITH_AES_128_GCM_SHA256
Client Random: 375f5632ba9075b88dd83eeeed4adb427d4011298efb79fb2bf78f4a4b7d9d95
Server Random: 5a1b3957e3bd1644e7083e25c64f137ed2803b680e43395a82e5b302b64ba763    
Master Secret: 2FB179AB70CD4CA2C1285B4B1E294F8F44B7E8DA26B62D00EE35181575EAB04C
           4FA11C0DA3ABABB4AF8D09ACB4CCC3CD

包11数据:

Direction is Client -> Server.
Secure Sockets Layer
    TLSv1.2 Record Layer: Application Data Protocol: Application Data
    Content Type: Application Data (23)
    Version: TLS 1.2 (0x0303)
    Length: 45
    Encrypted Application Data: c91de005e2ae50a8a57abee55c183667b136343feef4a387cb7cf83030a47e230af268378c4f33c8b5bab3d26d

到目前为止我做了什么:

主要推导:

我在这里只需要客户端密钥,因为我想要解密Client-> Server包.我根据RFC扩展了服务器和客户端密钥和IV. Client Write Key: 4B119DFBFC930ABE130030BD53C3BF78 Client Write IV: 2029CAE2

随机数:

我从salt(= Client Write IV)和显式nonce(=加密数据的前8个字节)创建AES-GCM nonce. Salt: 2029CAE2 explicitNonce: C91DE005E2AE50A8 Nonce: 2029CAE2C91DE005E2AE50A8

附加认证数据(AAD):

这是我显然陷入困境的地方.RFC5246说:

additional_data = seq_num + TLSCompressed.type + TLSCompressed.version + TLSCompressed.length; 其中"+"表示连接.

所以我做了这个:

byte[] aad = {0, 0, 0, 0, 0, 0, 0, 1,   // seq_no uint64
    0x17,               // type 0x17 = Application Data
    0x03, 0x03,             //  TLS Version 1.2
    0, 45};             // 45 Bytes of encrypted data

我认为seq_no是1.当Change Cipher Spec发送记录时,它会重置为零.(Packet #8)然后加密Finished记录有seq_no = 0.而下一个客户端数据包是我们Packet #11 的seq_no = 1.

码:

现在我把所有东西都送进了BouncyCastle:

AEADParameters parameters = new AEADParameters(new KeyParameter(clientWriteKey), 128, nonce, aad);
GCMBlockCipher gcmBlockCipher = new GCMBlockCipher(new AESFastEngine());
gcmBlockCipher.init(false, parameters);
byte[] plainText = new byte[gcmBlockCipher.getOutputSize(cipherText.length)];
try {
    int decLen = gcmBlockCipher.processBytes(cipherText, 0, cipherText.length, plainText, 0);
    decLen += gcmBlockCipher.doFinal(plainText, decLen);
} catch (InvalidCipherTextException e) {
    System.out.println("MAC failed: " + e.getMessage());
}

这总是抛出MAC失败:GCM中的mac检查失败.但解密的输出是正确的:

byte[] decomp = decompress(plainText);
System.out.println(new String(decomp, "UTF-8"));

这打印GET / HTTP/1.0\n.

解压助手:

public static byte[] decompress(byte[] data) throws IOException, DataFormatException {
    Inflater inflater = new Inflater(true);
    inflater.setInput(data);

    ByteArrayOutputStream outputStream = new ByteArrayOutputStream(data.length);
    byte[] buffer = new byte[1024];
    while (inflater.getRemaining() > 0) {
        int count = inflater.inflate(buffer);
        outputStream.write(buffer, 0, count);
    }
    outputStream.close();
    byte[] output = outputStream.toByteArray();

    inflater.end();
    return output;
    }

结论: 由于解密输出是正确的,我可以放心地假设密钥派生和解密工作正常.只有身份验证失败 所以我想也许我在使用附加认证数据(AAD)做错了.所以这个问题归结为:

如何正确组装附加认证数据(AAD)？

谢谢!

Answer 1

GCM 模式根据消息、关联数据和公共随机数计算 MAC，您对此进行了很好的介绍。

我认为你使用了错误的长度，在加密和附加MAC之前它应该是明文长度。尝试 45 - 8（显式随机数） - 16 (MAC) = 21。