[chbot] Introduction (was: Re: Last two and a bit days of the garage sale....)

[Sean Anderson]

Yeah that's a good one, and I think A5/2 (the weakened,
export-restricted crypto algorithm) is in use in NZ. It has a 2^16
work factor because of a particular arrangement of the algorithm:

"If you can get keystream from two frames 2^11 apart:
R4 will be the same for both, due to the clobbered bit (hmm...)
guess R4; then the clocking for R1, R2, R3 is known (double hmm…)
Now solve for R1, R2, R3
Keystream difference is a linear function of R1, R2, R3 difference, so
can solve using linear algebra
This reveals the key
Complexity: 216 simple dot-products  realtime!
Our code breaks A5/2 in ~ 10 milliseconds [BGW99]"

You really only need a PC to break A5/2. A5/1 is different, you need
5TB of pre-computed (with 100 FPGAs) data and one large FPGA. Too
expensive for me.
It's one reason to get a 3G phone which uses A5/3 (Kasumi) which is
not currently broken.

On Sun, Mar 23, 2008 at 4:10 AM,  <follower at rancidbacon.com> wrote:
> > I've been looking at DES encryption cracking.
>  Ah, I see...
>
>  I've read about a GSM/A5 cracking project before and found it
>  interesting: <http://wiki.thc.org/cracking_a5>
>
>
>
>  --Phil.
>
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