File Stream Encryption (using a Context Menu)

• Download source files - 250 Kb

This article makes use of the Crypto++ library, available here. To run compile the demo code, you will need to download the Windows version of the Crypto++ library and source files.

I suggest you read the Readme.txt file (found in the zip file) which contains a very good explanation on Debugging this DLL, along with source notes.

• Overview
• Obtaining the Crypto++ Library
• Implementation Notes
• Acknowledgements
• Other articles using Crypto++ v3.2

Overview

This was put together because I wanted to implement the file stream encryption (Crypto++ Library v3.2) from a Context Menu.

From a File (Context Menu)

From a Folder (Context Menu)

Implementation Notes

Because I was en/decrypting files, I needed to preserve the attributes of the file(s)... and check if the file was created ok (this was necessary because if the file was not created (e.g.: Wrong PassPhrase), I didn't want to try and set the attributes back to what the original file was).

void CFileProcess::SetAttributes(CString csFilename, BYTE btAttrib) 
{
    char* pFileName = csFilename.GetBuffer(csFilename.GetLength() + 1);
    CFileStatus status;

    // This is a MUST
    status.m_mtime = 0;

    // Set the file attribute member
    status.m_attribute = btAttrib;

    // Set the file attribute
    CFile::SetStatus( pFileName, status );
}

BYTE CFileProcess::GetAttributes(CString csFilename) 
{
    char* pFileName = csFilename.GetBuffer(csFilename.GetLength() + 1);
    CFileStatus status;

    // Get the file attribute
    CFile::GetStatus( pFileName, status );

    // return the file attribute
    return status.m_attribute;
}

BOOL CFileProcess::DoesFileExist(CString csFilename) 
{

    char* pFileName = csFilename.GetBuffer(csFilename.GetLength() + 1);
    CFileStatus status;

    // Return the existance of the file
    return (CFile::GetStatus( pFileName, status ));

}

I also didn't want the user to encrypt files in the Windows directory, so I look into the registry (via Robert Pittenger's CRegistry class) and find the SystemRoot entry and check it against the input file path.

I also created a function to recursive through the directories and en/decrypt the files...

void CFileProcess::FindDirFiles(CString csDirPath)
{

    WIN32_FIND_DATA wfd;
    HANDLE hFind;
    CString csText = _T("");

    // Check if the last char is a back-slash
    // (If not, put it there)
    if (csDirPath.Right(1) != "\\")
        csDirPath += _T("\\");

    // set the variable and add an astrix for 
    // the beginning of the directory search.
    csText = csDirPath + _T("*");

    // Iterate through dirs
    hFind = FindFirstFile(csText, &wfd);
    if (hFind != INVALID_HANDLE_VALUE) {
        do {

            // Check if "." or "..", if not...
            // Check if its a directory.
            if ((strcmp(wfd.cFileName,_T("."))) && 
                (strcmp(wfd.cFileName,_T(".."))) && 
                (wfd.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)) {

                CString csDirIn = _T("");

                // Set to the directory found.
                csDirIn = csDirPath + wfd.cFileName;

                // Recursively search
                FindDirFiles(csDirIn);
            }
        } while (FindNextFile(hFind, &wfd));

        // This is a MUST
        FindClose(hFind);
    }

    // Iterate through files
    //
    // set the variable and add an astrix-dot-astrix "*.*"
    // for the beginning of the file search.
    csText = csDirPath + _T("*.*");
    hFind = FindFirstFile(csText, &wfd);
    if (hFind != INVALID_HANDLE_VALUE) {
        do {

            // If NOT a directory...
            if ((wfd.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) == 0) {

                CString csIn = _T("");
                CString csOut = _T("");

                // Set to the file found.
                csIn = csDirPath + wfd.cFileName;

                // if we are decrypting...
                if (!pThreadInfo->bEncrypt) {
                    csOut = csIn.Left(csIn.GetLength() - 4);
                }
                else { // we are encrypting...just appent the extention
                    csOut = csIn + ".enf";
                }

                // Now, add the filename into the Array.
                //
                // this will be used later when we 
                // actually perform the en/decryption
                m_csFileArrayIn.Add(csIn);
                m_csFileArrayOut.Add(csOut);
            }
        } while (FindNextFile(hFind, &wfd));

        // This is a MUST
        FindClose(hFind);

    }
}

That's it!

Obtaining the Crypto++ Library

The simplest way to compile the demo application, having downloaded the Crypto++ files, is to provide the compiler with the paths needed to find the header files and the compiled library. You can set these up using the Tools | Options | Directories page from the VC IDE.

Download Crypto++ v3.2

Acknowledgements

Along with the Crypto++ library (see above), the demo was done by using a very good Explorer Context Menu Example written by Smaller Animals Software Copyright 1999, All Rights Reserved and this program may be freely distributed (see About Box and included Zip). This example has been included in the demo download (zipped).

The demo makes use of Robert Pittenger's CRegistry class and Chris Maunder's CHyperlink class (both classes have been included in the demo download).

Other Articles using Crypto++ v3.2

• CLogIt by Daniel Madden.
• Coming Soon..."MFCCryptLib" (it's the Crypto++ demo (found in the Zip) with an MFC interface).