The attached code will make it so that the RAND_screen function can be used
to seed OpenSSL on CE. It replaces the readscreen function provided with
the library in the crypto\rand\rand_win.c function. I have not tested it on
non-CE devices, so you may want to #ifdef it in if you will be supporting
standard Windows as well.
static void readscreen(void)
{
HDC hdc, hdcScr;
int nWidth, nHeight;
BITMAPINFO dibInfo;
BYTE *pBGR = NULL;
HBITMAP hNewBitmap, hOldBitmap;
int nBufSize;
int nChunkSize;
int y;
// Take a snapshot of the screen
hdcScr = GetDC(NULL);
hdc = CreateCompatibleDC(hdcScr);
// Get screen resolution
nWidth = GetDeviceCaps(hdc, HORZRES);
nHeight = GetDeviceCaps(hdc, VERTRES);
// Fill in the DIB structure
dibInfo.bmiHeader.biBitCount = 24;
dibInfo.bmiHeader.biClrImportant = 0;
dibInfo.bmiHeader.biClrUsed = 0;
dibInfo.bmiHeader.biCompression = 0;
dibInfo.bmiHeader.biHeight = nHeight;
dibInfo.bmiHeader.biPlanes = 1;
dibInfo.bmiHeader.biSize = 40;
dibInfo.bmiHeader.biSizeImage = nWidth*nHeight*3;
dibInfo.bmiHeader.biWidth = nWidth;
dibInfo.bmiHeader.biXPelsPerMeter = 3780;
dibInfo.bmiHeader.biYPelsPerMeter = 3780;
dibInfo.bmiColors[0].rgbBlue = 0;
dibInfo.bmiColors[0].rgbGreen = 0;
dibInfo.bmiColors[0].rgbRed = 0;
dibInfo.bmiColors[0].rgbReserved = 0;
// Create a new device independent bitmap and retrieve
// a pointer to its bit storage -- this is the raw
// bitmap data that will be hashed
hNewBitmap = CreateDIBSection(hdc,
(const BITMAPINFO*)&dibInfo,
DIB_RGB_COLORS, (void**)&pBGR, NULL, 0);
hOldBitmap = (HBITMAP) SelectObject(hdc, hNewBitmap);
// Copy the bitmap into the new device context -- this will
// also copy the bitmap to the DIB
BitBlt(hdc, 0, 0, nWidth, nHeight, hdcScr, 0, 0, SRCCOPY);
// Determine the buffer size of the screen data
nBufSize = 3 * nWidth * nHeight;
nChunkSize = nBufSize / ( 3 * 16 );
/* Now go through the whole screen, repeatedly grabbing n lines */
for ( y = 0; y < nBufSize; y += nChunkSize )
{
unsigned char md[MD_DIGEST_LENGTH];
/* Get the hash of the bitmap */
MD(pBGR + y, nChunkSize, md);
/* Seed the random generator with the hash value */
RAND_seed(md, MD_DIGEST_LENGTH);
}
// Restore the empty bitmap to the device context -- this
// clears up any potential resource leaks
SelectObject(hdc, hOldBitmap);
// Delete the DIB
DeleteObject(hNewBitmap);
// Done with the DCs.
DeleteDC( hdc );
DeleteDC( hdcScr );
}
The code is derived from an article in Dr. Dobb's Journal (December 2002,
"Automated Testing & Windows CE"), so you should have no problems
distributing it. Unfortunately, I haven't found a better way get random
information on the CE devices.
One additional suggestion would be to use the RAND_write_file and
RAND_load_file functions each time you exit and restart your application.
This will allow your randomness to "accumulate" each time your appliction is
run.
Brant Thomsen
Sr. Software Engineer
Wavelink Corporation
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] Behalf Of Antonio Ruiz
> Martínez
> Sent: Tuesday, March 22, 2005 12:23 PM
> To: openssl-users@openssl.org
> Subject: RAND_Bytes in Windows CE (Pocket PC or smartphone)
>
>
> Hello!
>
> I'm writing you because when I call to the function to make a pkcs#7
> enveloped data, I get the following error:
> 1673169562:error:2406064:random number generator:SSLEAY_RAND_BYTES_PRNG
> not seeded:.\crypto\rand\md_rand.c:503:You need to read the OpenSSL FAQ.
>
> I read it but the problems are related to Unix System, but what about
> Windows CE?
> Could you help me to solve it, please?
> Thanks in advance,
> Regards,
> Antonio.
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