Win32 Application CryptoAPI

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Date: Wed, 24 Nov 2004 18:35:01 -0800

Hi There,

I have been scanning the newsgroups for a solution to my problem and have
found that a few others are also experiencing the same problem but none of
the solutions provided to them seem to work for me.

I have a native Win32 application (written in C++) that needs to encrypt
some data, pass that data to a web service (written in C#) for decryption. I
just can't seem to decrypt the data correctly.

To demonstrate the problem, I have written a native Win32 (C++) application
to encrypt some data and write the encrypted data out to disk:

HCRYPTPROV hProv;
HCRYPTHASH hHash;
HCRYPTKEY hKey;
HANDLE hFile;
DWORD dwNumBytes, dwBytesWritten;
BYTE byPassword[] = {65, 66, 67, 68, 69, 70}; // equals "ABCDEF"
BYTE byData[] = {10, 20, 30, 40, 50, 60, 70, 80, 0, 0, 0, 0, 0, 0, 0,
0};
  
// Create the Cryptograhic Provider Object
if (CryptAcquireContext(&hProv, NULL, MS_DEF_PROV, PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT)) {
  // Create a hash object
  if (CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {
    // Hash in the password
    if (CryptHashData(hHash, byPassword, sizeof(byPassword), 0)) {
      // Derive a session key from the hash object.
      if (CryptDeriveKey(hProv, CALG_RC2, hHash, 0, &hKey)) {
        dwNumBytes = 8;
        if (CryptEncrypt(hKey, NULL, TRUE, 0, byData, &dwNumBytes,
sizeof(byData))) {
          // Create a file to store the encrypted data
          if ((hFile = CreateFile(_T("C:\\Encrypted.dat"), GENERIC_WRITE, 0,
NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL)) != INVALID_HANDLE_VALUE) {
            // Write the encrypted data out to file
            WriteFile(hFile, &byData, dwNumBytes, &dwBytesWritten, NULL);
            // Close the file handdle
            CloseHandle(hFile);
          }
        }
        // Destroy the session key
        CryptDestroyKey(hKey);
      }
    }
    // Destroy the hash object
    CryptDestroyHash(hHash);
  }
  // Release the cryptographic provider context
  CryptReleaseContext(hProv, 0);
}

I have also written a .NET C# application to read the data from file and try
and decrypt the data:

int iNumBytes;
FileStream fsData;
byte[] byData = new byte[16];
byte[] bySalt = {0,0,0,0,0,0,0,0};
byte[] byInitVect = {0,0,0,0,0,0,0,0};
                        
// Open the file containing the encrypted data, read inb the data and close
the file
fsData = File.Open("C:\\Encrypted.dat", FileMode.Open);
iNumBytes = fsData.Read(byData, 0, byData.Length);
fsData.Close();
                        
// Derive a session key from the password using an MD5 hash
PasswordDeriveBytes SessionKey = new PasswordDeriveBytes("ABCDEF", bySalt,
"MD5", 1);
                        
// Set up an RC2 cryptographic object
RC2CryptoServiceProvider Rc2 = new RC2CryptoServiceProvider();
Rc2.Mode = CipherMode.CBC;
Rc2.KeySize = 40;
Rc2.EffectiveKeySize = 40;
Rc2.BlockSize = 64;
Rc2.Key = SessionKey.GetBytes(5);

// Decrypt the data
ICryptoTransform decryptor = Rc2.CreateDecryptor(SessionKey.GetBytes(8),
byInitVect);
byte[] myOutputBytes = new byte[decryptor.OutputBlockSize];
iNumBytes = decryptor.TransformBlock(byData, 0, decryptor.InputBlockSize,
myOutputBytes, 0);

The problem is that the data just does not decrypt. I really don't care what
type of hashing or encryption algorithms are used so long as they are
supported on Win98/Me and NT4.0SP6/2000/XP/2003.

Any help in solving this problem would be greatly appreciated.

Thanks,

-Darren-

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