[ILUG] serious Debian/Ubuntu security hole found

[Timothy Murphy]

On Saturday 17 May 2008 04:14:02 pm Michael Watterson wrote:

> The two oscillators approach to HW RNG is ideally suited to IC
> fabrication with no analogue circuits. Analogue IC design are awkward,
> expensive and understood  by fewer designers and  don't lend themselves
> to FPGA or CPU as easily.  A resistor is awkward because the noise is
> small and any amplication needed prior to ADC could be unreliable. Using
> a cheap One Eur  Microchip  Inc  PIC  ADC  &  I2C or USB to host
> interface, you would use two similar zener diodes, one for the Vref and
> the other the input signal. This means any periodic noise not fully
> filtered from the supply rail would cancel out. Or read two zeners via
> ADC and correlate to remove any periodic interference or supply rail
> noise. Unlike a resistor the noise level of a Zener is very high, thus
> in practice even a simple ADC and one zener is found to give very good
> results.

As far as I can see, what you are saying is that you have a black box
which emits numbers, and you are convinced -
on what seems to me the vaguest of grounds -
that these numbers form a random sequence.

I don't see any evidence that this hypothesis has ever been tested.

Your argument boils down to the negative one
that you can't see any reason why the sequence should not be random.

Actually, most physical phenomena like this are periodic,
or nearly periodic, and while quantum fluctuations might cause
local irregularities, I would expect there to be long term patterns
of some kind.

Incidentally, I doubt if this is of any importance for cryptography,
since it doesn't seem to me to matter too much
if a seed is random, or just unpredictable.
However, the issue I have been debating is whether
a physical device is a better source of random or pseudo random numbers
than a well-designed mathematical algorithm.

To repeat my basic argument -
while quantum theory suggests methods of producing truly random sequences,
I don't believe any practical way of using this has yet been devised.
It is notoriously difficult to use quantum effects in this kind of way -
as the history, or non-history, of quantum computing shows.



-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland