Problem - Kevin Tafuro

if (cbOutput > cbHashData) goto done;
if (!(pbHashData = (BYTE *)LocalAlloc(LMEM_FIXED, cbHashData))) goto done;
DialogData.dEntropy = 0.0;
DialogData.cbRequested = cbOutput * 8;
DialogData.hHash = hHash;
DialogData.dwLastTime = 0;
GetCursorPos(&(DialogData.ptLastPos));
bResult = DialogBoxParam(hInstance, MAKEINTRESOURCE(SPC_MOUSE_DLGID),
hWndParent, MouseEntropyProc, (LPARAM)&DialogData);
if (bResult) {
if (!CryptGetHashParam(hHash, HP_HASHVAL, pbHashData, &cbHashData, 0))
bResult = FALSE;
else
CopyMemory(pbOutput, pbHashData, cbOutput);
}
done:
if (pbHashData) LocalFree(pbHashData);
if (hHash) CryptDestroyHash(hHash);
if (hProvider) CryptReleaseContext(hProvider, 0);
return bResult;
}
There are other ways to achieve the same result on Windows. For example, entropy
could be collected throughout your entire program by installing a message hook or
by moving the entropy collection code out of MouseEntropyProc( ) and placing it into
your program’s main message processing loop. SpcGatherMouseEntropy( ) could then
be modified to operate in global state, presenting a dialog only if there is not a sufficient
amount of entropy collected already.
Note that the dialog uses a progress bar control. While this control is a standard control
on Windows, it is part of the common controls, so you must initialize common
controls before instantiating the dialog; otherwise, DialogBoxParam( ) will fail inexplicably
(GetLastError( ) will return 0, which obviously is not very informative). The
following code demonstrates initializing common controls and calling
SpcGatherMouseEntropy( ):
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine,
int nShowCmd) {
BYTE pbEntropy[20];
INITCOMMONCONTROLSEX CommonControls;
CommonControls.dwSize = sizeof(CommonControls);
CommonControls.dwICC = ICC_PROGRESS_CLASS;
InitCommonControlsEx(&CommonControls);
SpcGatherMouseEntropy(hInstance, 0, pbEntropy, sizeof(pbEntropy));
return 0;
}
642 | Chapter 11: Random Numbers
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