解密密文时InvalidCiphertext异常 [英] InvalidCiphertext exception when decrypting ciphertext

问题描述

我正在使用一个新的安全通信协议，我有解密密文的问题。

I'm working in a new protocol for secure communication and I'm having problems to decrypt the ciphertext.

数据包保存在uint8_t *变量中并加密。直到这一部分都一切顺利。但是当我尝试解密我有以下问题：

The data packet is saved in a uint8_t* variable and encrypted. Until this part is all going well. But when I try to decrypt I got the followings problems:

1）如果我发送矢量和大小（它真的20，但我只是想解密最后16字节）：

1) If I send the vector and the size (it's really 20 but I just want to decrypt the last 16 bytes):

CBC_Mode< AES >::Decryption decryptor;
decryptor.SetKeyWithIV( key, CryptoPP::AES::DEFAULT_KEYLENGTH, iv );

CryptoPP::StringSource ss( vector+4, 16 , true,
        new CryptoPP::StreamTransformationFilter( decryptor,
             new CryptoPP::StringSink( decryptedtext ) ) );

我得到：

terminate called after throwing an instance of 'CryptoPP::InvalidCiphertext'
  what():  StreamTransformationFilter: invalid PKCS #7 block padding found

2）如果我只是发送不带大小的向量：

2) If I just send the vector without size:

CryptoPP::StringSource ss( vector+4, true,
       new CryptoPP::StreamTransformationFilter( decryptor,
              new CryptoPP::StringSink( decryptedtext ) ) );

程序运行，但我只是得到所有00：

The programs runs but I just get all 00:

Text Encrypted (20 bytes)
8c 97 b7 d8 74 80 3d 9f 9f 62 2e 93 38 c7 d1 b de a4 21 80 

Text Decrypted (16 bytes)
0 0 0 0 0 0 0 0 68 0 0 0 0 0 0 0 0 0 0 0 

我读到，可能是密钥没有正确生成，但我的工作大小为16，这里是我怎么做：

I read that it could be that the key is not generated correctly, but I'm working with a size of 16 and here is how I do it:

 byte key[ CryptoPP::AES::DEFAULT_KEYLENGTH ], iv[      CryptoPP::AES::BLOCKSIZE ];
 memset( key, 0x00, CryptoPP::AES::DEFAULT_KEYLENGTH );
 memset( iv, 0x00, CryptoPP::AES::BLOCKSIZE );

3）我还试图将向量转换为char并以字符串形式发送：

3) I also tried to cast the vector to char and send it like an string:

CryptoPP::StringSource ss( reinterpret_cast<const unsigned char*>( (vector + 4) ), 16, true,
        new CryptoPP::StreamTransformationFilter( decryptor,
            new CryptoPP::StringSink( decryptedtext ) ) );

但我再次得到同样的结果：

But again I get the same thing:

terminate called after throwing an instance of 'CryptoPP::InvalidCiphertext'
  what():  StreamTransformationFilter: invalid PKCS #7 block padding found

请帮助，我已经尝试了几天来弄清楚是什么问题。这花了我太长时间，我找不到解决方案。

Please help, I have tried for days to figure out what's wrong. This is taking me too long and I can't find the solutions.

有没有人知道可能发生什么？

Does anyone have any idea on what might be happening?

如果您需要更多详细信息，代码或任何内容，请与我们联系。

Let me know if you need further details, code or anything.

编辑：

4）我尝试的另一件事情是（构建解密器的另一种方法）：

4) One more thing that I tried was (another way to construct the decrypter):

CryptoPP::AES::Decryption aesDecryption(key, CryptoPP::AES::DEFAULT_KEYLENGTH);
CryptoPP::CBC_Mode_ExternalCipher::Decryption cbcDecryption( aesDecryption, iv );


CryptoPP::StreamTransformationFilter stfDecryptor(cbcDecryption, new CryptoPP::StringSink( decryptedtext ) );
stfDecryptor.Put( reinterpret_cast<const unsigned char*>( (vector + 4) ), 16 );
stfDecryptor.MessageEnd();

但我得到：

terminate called after throwing an instance of 'CryptoPP::InvalidCiphertext'
  what():  StreamTransformationFilter: invalid PKCS #7 block padding found

Edit2：

使用此行创建向量因为我使用一个平台进行网络编码，所以很复杂）：

The vector is created with this line (the way the vector is fulled is a quite complicated to put it here because I am using a platform for network encoding) :

uint8_t* vector;

Edit3：

加密向量。

CryptoPP::AES::Encryption aesEncryption(key, CryptoPP::AES::DEFAULT_KEYLENGTH);
        CryptoPP::CBC_Mode_ExternalCipher::Encryption cbcEncryption( aesEncryption, iv );

        CryptoPP::StreamTransformationFilter stfEncryptor(cbcEncryption, new CryptoPP::StringSink( ciphertext ) );
        stfEncryptor.Put( reinterpret_cast<const unsigned char*>( (vector + 4) ), 16 );
        stfEncryptor.MessageEnd();

然后我把密文再次放在向量中：

And after that I put the ciphertext again in the vector:

std::cout << std::endl << std::endl;
for(int i=0;i < 16; i++){
    *(vector+ i + 4) = (ciphertext[i]) ; 
}

推荐答案

问题是编码与填充和试图解密它没有。

The problem was that I was encoding with padding and trying to decrypt it without. So I add not only in the encryption but in the descryption that it should work without padding.

创建密钥和IV：

CBC_Mode< AES >::Encryption encryptor;
encryptor.SetKeyWithIV( key, CryptoPP::AES::DEFAULT_KEYLENGTH, iv );

加密：

CryptoPP::StringSource ss( vector + 4 , 16, true, 
     new CryptoPP::StreamTransformationFilter( encryptor,
          new CryptoPP::StringSink( ciphertext ),
              CryptoPP::StreamTransformationFilter::NO_PADDING
     ) // StreamTransformationFilter      
); // StringSource

解密：

CBC_Mode< AES >::Decryption decryptor;
    decryptor.SetKeyWithIV( key, CryptoPP::AES::DEFAULT_KEYLENGTH, iv );

        CryptoPP::StringSource ss( reinterpret_cast<const unsigned char*>( (vector + 4) ), 16, true,
                new CryptoPP::StreamTransformationFilter( decryptor,
                    new CryptoPP::StringSink( decryptedtext ), CryptoPP::StreamTransformationFilter::NO_PADDING) );

我这样做是因为我不想使用填充。

I did this because I don't want to work with padding anymore.

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