On Sun, Dec 17, 2000 at 10:50:57PM +0100, Karel Kulhavy wrote:
> I noticed peculiarities in the behaviour of the delta-delta-3 system for
> entropy estimation in the random.c code./ When I hold right alt or control, I
> get about 8 bits of entropy per repeat fro the /dev/random which is
> overestimated. I think the real entropy is 0 bits because it is absolutely
> deterministic when the interrupt comes. Am I right or is there any hidden
not absolutely, but we should ignore repeated keys that generate more than
one scancode.
tytso, here's the patch to do it again:
--- linux/drivers/char/random.c Sun Jul 30 18:01:23 2000
+++ linux-prumpf/drivers/char/random.c Thu Sep 28 17:07:03 2000
@@ -763,10 +763,15 @@
void add_keyboard_randomness(unsigned char scancode)
{
- static unsigned char last_scancode = 0;
- /* ignore autorepeat (multiple key down w/o key up) */
- if (scancode != last_scancode) {
- last_scancode = scancode;
+ static unsigned char last_scancode[2] = { 0, 0 };
+
+ /* ignore autorepeat (multiple key down w/o key up).
+ * add_keyboard_randomness is called twice for certain AT keyboard
+ * keys, so we keep a longer history. */
+ if (scancode != last_scancode[0] &&
+ scancode != last_scancode[1]) {
+ last_scancode[0] = last_scancode[1];
+ last_scancode[1] = scancode;
add_timer_randomness(&keyboard_timer_state, scancode);
}
}
If we want to rely solely on the add_timer_randomness checks, we should
remove the autorepeat check completely.
Philipp Rumpf
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