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Harald Welte laforge at gnumonks.orgHi all,
recently I've been mentioning A5/4 in a couple of meetings. I've found
the (already approved) change requests that introduce A5/4 by coincidence
today:
http://www.3gpp.org/ftp/tsg_sa/TSG_SA/TSGS_45/docs/SP-090635.zip
http://www.3gpp.org/ftp/tsg_sa/TSG_SA/TSGS_46/docs/SP-090821.zip
So basically A5/4 (and GEA4) use a 128bit Kc, and this mandates the use
of an USIM in USIM application mode. Old GSM SIM cards are not sufficient.
So A5/4 will be the first algorithm that uses a different Kc and will thus
not suffer from semi-active downgrading attacks (like you can do with old
phones and A5/2 to break A5/1 or A5/3, or you can do today with A5/3 if you
later use the same RAND on an A5/1 encrypted session).
Regards,
Harald
--
- Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/
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