Problem - Kevin Tafuro

SpcGatherKeyboardEntropy( ) uses the CryptoAPI to hash the data collected from the
keyboard. It first acquires a context object, then creates a hash object. After the arguments
are validated, the dialog resource is loaded by calling CreateDialog( ), which
creates a modeless dialog. The dialog is created modeless so that keyboard messages
can be captured. If a modal dialog is created using DialogBox( ) or one of its siblings,
message handling for the dialog prevents us from capturing the keyboard messages.
Once the dialog is successfully created, the message-handling loop performs normal
message dispatching, calling IsDialogMessage( ) to do dialog message processing.
Keyboard messages are captured in the loop prior to calling IsDialogMessage( ), however.
That’s because IsDialogMessage( ) causes the messages to be translated and dispatched,
so handling them in the dialog’s message procedure isn’t possible.
When a key is pressed, a WM_KEYDOWN message will be received, which contains information
about which key was pressed. When a key is released, a WM_KEYUP message
will be received, which contains the same information about which key was released
as WM_KEYDOWN contains about a key press. The keyboard scan code is extracted from
the message, combined with a timestamp, and fed into the hash object. If the current
scan code is the same as the previous scan code, it is not counted as entropy but
is added into the hash anyway. As other keystrokes are collected, the progress bar is
updated, and when the requested amount of entropy has been obtained, the OK button
is enabled.
When the OK button is clicked, the dialog is destroyed, terminating the message
loop. The output from the hash function is copied into the output buffer from the
caller, and internal data is cleaned up before returning to the caller.
#include
#include
#include
#define SPC_ENTROPY_PER_SAMPLE 0.5
#define SPC_KEYBOARD_DLGID 101
#define SPC_PROGRESS_BARID 1000
#define SPC_KEYBOARD_STATIC -1
typedef struct {
BYTE bScanCode;
DWORD dwTickCount;
} SPC_KEYPRESS;
static BOOL CALLBACK KeyboardEntropyProc(HWND hwndDlg, UINT uMsg, WPARAM wParam,
LPARAM lParam) {
HWND *pHwnd;
if (uMsg != WM_COMMAND || LOWORD(wParam) != IDOK ||
HIWORD(wParam) != BN_CLICKED) return FALSE;
pHwnd = (HWND *)GetWindowLong(hwndDlg, DWL_USER);
DestroyWindow(hwndDlg);
Gathering Entropy from the Keyboard | 635
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