Re: Problems with A5/3 encryption

Hi Jan,

Do you have traces of the attach/authentication? It seems like for some reason your MS don't like A5/3, because they are supposed to reply with Cipher Mode Complete. So top of my head I had the thought there might be something wrong with the initial establishment of the keys.

Cheers, Domi

2018. márc. 6. dátummal, 10:58 időpontban Bruckner Jan (ETAS-SEC/ECT-Mu) Jan.Bruckner@escrypt.com írta:

Dear list,

I’m having trouble using the A5/3 encryption in my setup. A5/1 works perfectly fine [attachment a5_1.pcapng]. As soon as I switch to A5/3 and e.g. send an SMS, the last valid message I see in the Wireshark traces of the GSMTAP of osmo-bts-trx is the Ciphering Mode Command requesting A5/3. After that, several messages arrive at the bts, but it seems like it can’t make any sense of them. The MS repeatedly tries to send the SMS but never succeeds [attachment a5_3.pcapng]. Both MSs are connected to the same bts.

According to the Classmarks of all MSs, A5/1 as well as A5/3 are supported. This is my Setup:

•   USRP N210
  

•   osmo-trx
  

•   osmo-bts-trx
  

•   osmo-nitb
  

•   osmo-pcu
  

•   osmo-sgsn
  

•   osmo-ggsn
  

I’m using a Debian 9 VM and tried both the packages from osmocom-latest as well as osmocom-nightly. The MSs I’ve tested are two Nexus 6 and one Samsung Galaxy S I9000. All three with sysmocom nano USIMs.

Could the decryption at the bts be incorrect? Has anyone tested/used it recently? I’ll be happy to provide additional information if needed.

Thanks, Jan <a5_3.pcapng><a5_1.pcapng>