12 Jan
2018
12 Jan
'18
2:44 p.m.
On Fri, Jan 12, 2018 at 08:23:05AM +0000, Radiarisainana Sitraka wrote:
Hello,I have some question, it just for curiosity!
It's possible that a phone tell to the bts he did support only A5/0 encryption or it
just only the BTS to command the ciphering !? and it is possible to do that for the
osmocomBB !?
Whether to do Auth / Ciph is up to the MSC to decide. According to spec, phones
are required to at least support A5/1. By coincidence, there has been a patch
in that area recently:
https://gerrit.osmocom.org/#/c/5560/2/src/libmsc/gsm_04_08.c
So in principle, there are flags in Classmark 1, 2 and 3 indicating what A5s
are supported by the MS, and the MSC matches them up with its own policy.
However, any "real" MSC out there is likely to request at least A5/1
Authentication, regardless of your Classmark bits. If A5/1 is marked
unsupported, it could even reject your MS altogether. But yes, you could send
a crafted Classmark with all A5/N marked unsupported, and that should be
possible with osmocom-bb. In the unlikely event that you get through with that,
you've found an MSC bug / misconfiguration.
~N