[Dev-C++] Crypto

[Rick D. <ric...@oc...>]

I'm trying to encrypt a file and to be honest I don't have a clue how to do
it. SO I copied and pasted the example from the MSDN encryption example but
it keeps failing on this if statement:

// Get a handle to key exchange key.
if(!CryptGetUserKey(hProv, AT_KEYEXCHANGE, &hXchgKey)) {
    printf("Error %x during CryptGetUserKey!\n", GetLastError());
    goto done;
}

The error translates to key doesn't exist. OK but how do I create it? Or is
the example in the MSDN flawed somehow?


I've pasted my slightly modified code below. Any assitance would be
appreciated.

#include <windows.h>
#include <wincrypt.h>
#include <stdio.h>
#include "resource.h"

extern void OutputErrorMessage();
extern void OutputDistinctErrorMessage(char *msg);

#define BLOCK_SIZE 160
#define BUFFER_SIZE (BLOCK_SIZE+16) // Give buffer 16 bytes of extra
                                    // room for padding, and so forth.

BOOL SaveEncryptedTextFileFromEdit(HWND hEdit, LPCTSTR pszFileName)
{
	HANDLE hFile;
	BOOL bSuccess = FALSE;
    FILE *hDest = NULL;
    int eof = 0;

    HCRYPTPROV hProv = 0;
    HCRYPTKEY hKey = 0;
    HCRYPTKEY hXchgKey = 0;


    BYTE pbBuffer[BUFFER_SIZE];
    DWORD dwCount;

    BYTE *pbKeyBlob = NULL;
    DWORD dwBlobLen;

    DWORD dwTextLength;

	hFile = CreateFile(pszFileName, GENERIC_WRITE, 0, NULL,
		CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
	if(hDest != INVALID_HANDLE_VALUE)
	{

        // Get a handle to the default provider.
        if(!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0)) {
            OutputErrorMessage();
            goto done;
        }


        // Create a random block cipher session key.
        if(!CryptGenKey(hProv, CALG_RC2, CRYPT_EXPORTABLE, &hKey)) {
            OutputErrorMessage();
            goto done;
        }

        // Get a handle to key exchange key.
        if(!CryptGetUserKey(hProv, AT_KEYEXCHANGE, &hXchgKey)) {
            OutputErrorMessage();
            goto done;
        }

        // Determine the size of the key blob and allocate memory.
        if(!CryptExportKey(hKey, hXchgKey, SIMPLEBLOB, 0, NULL, &dwBlobLen))
{
            OutputErrorMessage();
            goto done;
        }
        if((pbKeyBlob = (BYTE *) malloc(dwBlobLen)) == NULL) {
            OutputErrorMessage();
            goto done;
        }

        // Export the key into a simple key blob.
        if(!CryptExportKey(hKey, hXchgKey, SIMPLEBLOB, 0, pbKeyBlob,
                &dwBlobLen)) {
            OutputErrorMessage();
            free(pbKeyBlob);
            goto done;
        }

        // Write the size of the key blob to the destination file.
        fwrite(&dwBlobLen, sizeof(DWORD), 1, hDest);
        if(ferror(hDest)) {
            OutputErrorMessage();
            free(pbKeyBlob);
            goto done;
        }

        // Write the key blob to the destination file.
        fwrite(pbKeyBlob, 1, dwBlobLen, hDest);
        if(ferror(hDest)) {
            OutputErrorMessage();
            free(pbKeyBlob);
            goto done;
        }

        // Free memory.
        free(pbKeyBlob);


		dwTextLength = GetWindowTextLength(hEdit);
		// No need to bother if there's no text.
		if(dwTextLength > 0)
		{
			char * pszText;
			DWORD dwBufferSize = dwTextLength + 1;

			pszText = (char *) GlobalAlloc(GPTR, dwBufferSize);

			if(pszText != NULL)
			{
				if(GetWindowText(hEdit, pszText, dwBufferSize))
				{
					DWORD dwWritten;
					// Encrypt the data.
                    if(!CryptEncrypt(hKey, 0, eof, 0, pbBuffer, (DWORD *)
pszText,

dwBufferSize))
                    {
                        char *nmsg = "Error during CryptEncrypt!\n";
                        OutputDistinctErrorMessage(nmsg);
                        goto done;
                    }

                    // Write the data to the destination file.
                    fwrite(pbBuffer, 1, dwCount, hDest);
                    if(ferror(hDest)) {
                        printf("Error writing data!\n");
                        goto done;
                    }

					if(WriteFile(hFile, pszText, dwTextLength, &dwWritten, NULL))
						bSuccess = TRUE;
				}
				GlobalFree(pszText);
			}
		}
		CloseHandle(hFile);
	}

    done:

        // Destroy the session key.
        if(hKey != 0) CryptDestroyKey(hKey);

        // Destroy the key exchange key.
        if(hXchgKey != 0) CryptDestroyKey(hXchgKey);

        // Release the provider handle.
        if(hProv != 0) CryptReleaseContext(hProv, 0);

        // Close the source file.
        //if(hSource != NULL) fclose(hSource);

        // Close destination file.
        if(hDest != NULL) fclose(hDest);


	return bSuccess;
}