Serializing encrypted data

• Download demo project - 47 Kb

Introduction

I've recently discovered the CArchive class. I've never used it before. I had to save my application's preferences and I thought I would try to serialize it to a file using the CArchive class. Then only problem is that I need to encrypt the data.

So I sat down and wrote a CFile derived class to encrypt data while saving it.

In the demo project I've used the Rijndael algorithm. The implementation was written by Szymon Stefanek.

Description

The most important functions of the CFile class are Read and Write. Since these are virtual functions, you can override them with your own functions.

In the class, there are 2 callback functions. The class uses both to encrypt and to decrypt the data.

typedef UINT (FileEncryptProc)(const BYTE *pBuffer,UINT dwSize,BYTE *pDestination,DWORD dwParam);

Parameters:

• pBuffer - Pointer to the data
• dwSize - Data length in bytes
• pDestination - Pointer to a destination buffer
• dwParam - User defined parameter

Return value:

New data length.

Usage

You set the callbacks using the SetEncryption function

//  These are the encryption and decryption functions

UINT Encrypt(const BYTE *pBufIn, UINT nSize, BYTE *pBufOut, 
             DWORD dwParam)
{
    return ((Rijndael*)dwParam)->padEncrypt(pBufIn, 
        nSize, pBufOut);
}

UINT Decrypt(const BYTE *pBufIn, UINT nSize, BYTE *pBufOut, 
             DWORD dwParam)
{
    return ((Rijndael*)dwParam)->padDecrypt(pBufIn, 
        nSize, pBufOut);
}

f.SetEncryption(&Encrypt, (DWORD)&rijEncrypt, &Decrypt, 
                (DWORD)&rijDecrypt); // Set the encryption callbacks

Conclusion

In the demo project, I've created two Rijndael objects. One for encryption and one for decryption. Both objects were initialized using the same key. I've also created a CFileEx object and set it's callbacks to my defined functions.

From that point, I can create a CArchive object and use it as normal with my file. As you can see in the demo, I am writing and reading various data types to and from the archive.

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