Question on Uplink 'sequence count' handling in MME
laforge at gnumonks.org
Sat Jul 13 13:18:47 UTC 2019
Hi Sukchan and list,
I'm currently reading the MME code and I'm having some trouble understanding
the handling of the uplink counter for NAS security.
I only see mme_ue->ul_count.i32 ever being set to '0' when a new security
context is used. But I don't see it ever being incremented? I only see
ul_count.sqn incremented, but then the nas_mac_calculate() always gets
ul_count.i32 passed as input.
So I'm somehow not understanding how the MAC can ever verify on any uplink
message beyond/after the first one which establishes a new security context.
What am I missing? Thanks for your insight!
- Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
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