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
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