从C＃调用时从CFB模式截断的输出 [英] Truncated output from CFB mode when calling from C#

问题描述

我有一个很讨厌的问题，我无法解决2天。我有一个 encrypt（）方法，使用C ++编写的Crypto ++库。该方法实现如下：

  string CRijndaelHelper :: Encrypt（string text）
 {
 CFB_Mode< ; AES> ::加密e; 
 e.SetKeyWithIV（_key，sizeof（_key），_iv）; 
 
 string cipher，encoded; 
 
 // CFB模式不能使用填充。指定
 //一个方案将导致一个异常
 StringSource ss（text，true，
 new StreamTransformationFilter（e，
 new StringSink（cipher）
） 
 
 return cipher; 
}; 
 

当我在本地环境中调用这个方法时，它完美地工作，加密整个26Kb xml字符串，问题。

最后，我不得不在C＃代码中实现加密，为此我在native dll中编写了下面的包装代码，以供以后使用PInvoke：

  externC
 API_EXPORT char * _cdecl encrypt（char * contents）
 {
 string cont（contents）; 
 CRijndaelHelper rij; 
 string transformedText = rij.Encrypt（cont）; 
 return marshalReturn（transformedText）; 
} 
  

PInvoke部分如下：

  [DllImport（EncryptDecrypt.dll，CharSet = CharSet.Auto，CallingConvention = CallingConvention.Cdecl）] 
 [return：MarshalAs（UnmanagedType.LPStr ）] 
 public static extern string encrypt（[MarshalAs（UnmanagedType.LPStr）] string contents）; 
  

并且一切看起来工作完美，除了我在 transformedText 变量只有第一个540字节加密，这是所有。

请指教。

解决方案

...返回一个从本地代码调用时正确加密的字符串

问题不是C ++ encrypt ，它使用 std :: string 。问题是将它回归到托管代码作为 char * 。

更改 CRijndaelHelper :: Encrypt 到以下内容以删除嵌入的 NULL ，它将以1/255的概率自由地散布：

  #include< cryptopp / base64.h> 
使用CryptoPP :: Base64Encoder; 
 ... 
 
 string CRijndaelHelper :: Encrypt（string text）
 {
 CFB_Mode< AES> :: Encryption e; 
 e.SetKeyWithIV（_key，sizeof（_key），_iv）; 
 
 string cipher，encoded; 
 
 // CFB模式不能使用填充。指定
 //方案将导致异常
 StringSource ss（text，true，
 new StreamTransformationFilter（e，
 new Base64Encoder（
 new StringSink 
）））; 
 
 return cipher; 
}; 
  

使用 Base64 编码， a char * 将不截断遇到的第一个 NULL 字节的加密结果。 / p>

然后，对于解密：

  StringSource ss（cipher，true， 
 new Base64Decoder（
 new StreamTransformationFilter（d，
 new StringSink（text）
）））; 
  

I have pretty annoying issue which I'm unable to solve for 2 days. I have an encrypt() method which makes use of Crypto++ library written in C++. The method is implemented as follows:

string CRijndaelHelper::Encrypt(string text)
{
    CFB_Mode< AES >::Encryption e;
    e.SetKeyWithIV(_key, sizeof(_key), _iv);

    string cipher, encoded;

    // CFB mode must not use padding. Specifying
    //  a scheme will result in an exception
    StringSource ss(text, true,
        new StreamTransformationFilter(e,
            new StringSink(cipher)
        ));     

    return cipher;
};

When I call this method within the native environment it works perfectly, encrypting the whole 26Kb xml string without any problem.

Eventually I've had to implement the encryption in C# code, for that purpose I wrote the following wrapper code in native dll for later use with PInvoke:

extern "C"
API_EXPORT char* _cdecl encrypt(char* contents)
{   
    string cont(contents);
    CRijndaelHelper rij;
    string transformedText = rij.Encrypt(cont);     
    return marshalReturn(transformedText);  
}

While the PInvoke part looks as follows:

[DllImport("EncryptDecrypt.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.Cdecl)]
[return: MarshalAs(UnmanagedType.LPStr)]
public static extern string encrypt([MarshalAs(UnmanagedType.LPStr)] string contents);

And everything looks working perfect except that I get in transformedText variable only first 540 bytes encrypted and that's all.

Please advise.

解决方案

... returns a string which is correctly encrypted when invoked from native code

The problem is not you C++ encrypt, which uses a std::string. The problem is with marshalling it back to managed code as a char*.

Change CRijndaelHelper::Encrypt to the following to remove the embedded NULL that will be sprinkled liberally with a probability of 1/255:

#include <cryptopp/base64.h>
using CryptoPP::Base64Encoder;
...

string CRijndaelHelper::Encrypt(string text)
{
    CFB_Mode< AES >::Encryption e;
    e.SetKeyWithIV(_key, sizeof(_key), _iv);

    string cipher, encoded;

    // CFB mode must not use padding. Specifying
    //  a scheme will result in an exception
    StringSource ss(text, true,
        new StreamTransformationFilter(e,
            new Base64Encoder(
                new StringSink(cipher)
        )));     

    return cipher;
};

With the Base64 encoding, the marshaling as a char* will not truncate the encryption results on the first NULL byte encountered.

Then, for decryption:

StringSource ss(cipher, true,
    new Base64Decoder(
        new StreamTransformationFilter(d,
            new StringSink(text)
    )));   

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