Re: The Blum-Blum-Shub generator and a guessable seed



On Sat, 08 Apr 2006 12:02:00 +0200, Kristian Gjøsteen wrote:

Steven Jones <sjones@xxxxxxxxxx> wrote:
You should reread what I wrote. One of the steps described is
unpredictable. Can you find out which one? Try and think out of the box.

This will be much simpler if you (correctly) assume that I am stupid and
try to be explicit.

The unpredictability comes in with the instants at which the counter is
read. In my example, the first read operation is assumed to take place at
an unpredictable time, whereas the second one happens at an unpredictable
instant between 0 and 5 seconds after the first read. Given the rate at
which the counter is updated (10^9 times per second) and the fact the we
extract 16 bits in each read operation, any of the 65536 possible values
of those 16 bits is equally likely.

The entropy is not in the counter, but in how it is accessed.




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