Hi Sylvain,
On Thu, Jan 07, 2010 at 02:22:58PM +0100, Sylvain Munaut wrote:
AFAIK, the phone only keeps the data from last
authentication ( Kc & key_seq
).
When you send a CIPHER MODE COMMAND, it will use the last negotiated one, no
choice there.
of course. I meant you can keep multiple of them so you can select one of
them before doing an AUTH COMMAND
Keeping multiple AuthTuple for a subscriber would be
useless since only the
last one has usable data. And it's even easier if we only keep one because
this way, to find the next "key sequence", we can just take the old stored
one and increment it ...
The idea of the AuthTuple is as follows:
* you don't know the Ki of a SIM card
* you still want to use authentication/encryption
* so you send a couple of challenges to the SIM, remember the RAND
and record the SRES + Kc that you get
now every time you want to authenticate that sim, you randomly select one of
your known AuthTuples and send the recorded RAND, compare the SRES.
--
- Harald Welte <laforge(a)gnumonks.org>
http://laforge.gnumonks.org/
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