Mailing List Archive

Hi folks,

I recently downloaded gnupg-0.9.1 and compiled it on my Solaris
7 box (gcc v2.8.1). I ran "gpg --gen-key" and after entering my
pass phrase, gpg entered an infinite loop. I managed to track
this down to gather_random() in cipher/rndunix.c.

Consider the (snipped) code below:

672 static int
673 gather_random( void (*add)(const void*, size_t, int), int requester,
674 size_t length, int level )
675 {

...

703 while( length ) {

...

732 n = msg.ndata;
733 if( n > length )
734 n = length;
735 (*add)( msg.data, n, requester );
736
737 /* this is the trick how e cope with the goodness */
738 length -= (ulong)n * goodness / 100;
739 }

Now, if the remaining length is 1 (happened to me), the following
happens:

msg.ndata == 500
goodness == 86
length == 1

732 n = msg.ndata;

goodness == 86
length == 1
n == 500

733 if( n > length )
734 n = length;

goodness == 86
length == 1
n == 1

735 (*add)( msg.data, n, requester );
736
737 /* this is the trick how e cope with the goodness */
738 length -= (ulong)n * goodness / 100;

(ulong)n * goodness / 100 == 0
length == 1

739 }

Result: infinite loop.
There are two ways around this:

-----
737 {
738 /* This is the trick how we cope with the goodness. */
739 ulong subtract = (ulong)n * goodness / 100;
740 length -= subtract ? subtract : 1;
741 }
-----

Or:

-----
737 {
738 /* This is the trick how we cope with the goodness. */
739 ulong subtract = (ulong)msg.ndata * goodness / 100;
740 length -= subtract <= length ? subtract : length;
741 }
-----

The second one tends to use less iterations (with high goodness and low
length, one iteration is usually enough), while the first one typically
takes more (in my case 4 versus 1).

I chose to use the first, on the assumption that more iterations give
me more randomness, but that's more a gut feeling than anything else.
Either way it works.

Lemme know if I'm completely off (or marginally right).

Cheers,
Steven