Cruising the stacks and finding stuff
Allen
netsecurity at sound-by-design.com
Fri Apr 18 23:02:28 EDT 2008
[Moderator's note: I think Allen's math is rather seriously off here,
but I'll let other people address that --Perry]
Hi gang,
Back in the old days when there were public stacks in the San
Francisco Library I used to love to just wander and see what came
to hand. In the early days of the net there was Archie and Gopher
and they were great fun. The search engines took some of the
randomness out of that kind of stack searching so I found Peter's
reference to http://eprint.iacr.org/2008/166 very nostalgic and
spent a bit of time wandering around to find, by chance,
http://eprint.iacr.org/2008/147 where they are talking about
cracking A5/1 GSM in middling real time at about ~7 hours using
only 64 bits of the stream.
They were doing it using hardware costing less than a few grand,
I'd guess, given that the core chips are 120 Xilinx
Spartan3-XC3S1000 FPGAs at a cost of about $10/each. It isn't
hard to imagine that a three letter agency is reading A5/1 in
near to real time after a burp to kick start the decryption.
Granted A5/1 is known to be very weak, but how much weaker than
AES-128? Ten orders of magnitude? I haven't a clue and can't find
any estimate to compare AES-128 with A5/1 so I'll just use that
10 orders as a stake in the sand. Next, let's assume that the
machine, COPACOBANA, cost $10K. Assume non-linear speed
improvements with more chips so 10 times the size is only 6 times
as fast. Assuming these metrics then a machine costing ~$10M
would take ~2 minutes to start spitting out the decrypted stream.
Add Moore's Law, a bigger budget and a more efficient machine,
how long before AES-128 can be decoded in less than a day?
It does make one ponder.
May your nightmares never survive sunrise,
Allen
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