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Re: /dev/random is probably not
From: Chris Kuethe <chris.kuethe () gmail com>
Date: Tue, 5 Jul 2005 21:07:56 -0600

On 7/4/05, Robert Foxworth <rfoxwor1 () tampabay rr com> wrote:
At the last place at which I worked, a few years ago, a "random
number" was generated, and used in a FIPS 140-1 compliant
encryption device, by capturing 128 ethernet frames in sequence
from the local in-house network, gathering the LSB from the
arrival time of each frame, and using those values to generate
an encryption key. This was part of the "activation sequence"
which had to be done, once, on each such device.

Any studies out there on the randomness of such a number?
At first glance a non-deterministic network would seem to be
able to generate a useful number for the key.

OK, here's a quick set back-o-the-perl-script set of numbers.

I sampled a million packets off one of my fairly well used internet
links in 120.932020 seconds (according to tcpdump). I also sampled
209174 packets from my lan in 12507.724721 seconds (also according to
tcpdump).

Obviously I took the microsecond timestamp and extracted the low bit
for further processing. From these samples I grabbed a few 128bit
chunks from not-specially-selected offsets...

internet:
1000000 bits counted, 499888 x 0, 500112 x 1, longest string 30 bits
long was of 0
128 bits counted, 62 x 0, 66 x 1, longest string 10 bits long was of 1
128 bits counted, 57 x 0, 71 x 1, longest string 12 bits long was of 1
128 bits counted, 63 x 0, 65 x 1, longest string 10 bits long was of 1
128 bits counted, 68 x 0, 60 x 1, longest string 8 bits long was of 1
128 bits counted, 70 x 0, 58 x 1, longest string 8 bits long was of 0
128 bits counted, 76 x 0, 52 x 1, longest string 11 bits long was of 0
128 bits counted, 69 x 0, 59 x 1, longest string 8 bits long was of 0
128 bits counted, 61 x 0, 67 x 1, longest string 8 bits long was of 1
128 bits counted, 73 x 0, 55 x 1, longest string 11 bits long was of 0
128 bits counted, 74 x 0, 54 x 1, longest string 11 bits long was of 0

lan:
209174 bits counted, 104452 x 0, 104722 x 1, longest string 20 bits
long was of 0
128 bits counted, 56 x 0, 72 x 1, longest string 8 bits long was of 1
128 bits counted, 58 x 0, 70 x 1, longest string 7 bits long was of 1
128 bits counted, 54 x 0, 74 x 1, longest string 8 bits long was of 1
128 bits counted, 64 x 0, 64 x 1, longest string 6 bits long was of 0
128 bits counted, 66 x 0, 62 x 1, longest string 8 bits long was of 1
128 bits counted, 55 x 0, 73 x 1, longest string 11 bits long was of 1
128 bits counted, 73 x 0, 55 x 1, longest string 8 bits long was of 0
128 bits counted, 63 x 0, 65 x 1, longest string 6 bits long was of 1
128 bits counted, 64 x 0, 64 x 1, longest string 8 bits long was of 1
128 bits counted, 68 x 0, 60 x 1, longest string 6 bits long was of 1

CK

-- 
GDB has a 'break' feature; why doesn't it have 'fix' too?


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