Problems with A5/3 encryption

This is merely a historical archive of years 2008-2021, before the migration to mailman3.

A maintained and still updated list archive can be found at https://lists.osmocom.org/hyperkitty/list/OpenBSC@lists.osmocom.org/.

Bruckner Jan (ETAS-SEC/ECT-Mu) Jan.Bruckner at escrypt.com
Wed Apr 18 13:21:27 UTC 2018


Hi,

I migrated my setup to the new Network In The Box configuration with separated components (from latest, not nightly). I tested whether the described issue with A5/3 is resolved, but it still does not work. Though, the behavior has changed.

In the old setup a Ciphering Mode Command for A5/3 was sent, but a Ciphering Mode Complete was never received. Probably, what was happening is the following:
> The details there are that the Ciphering Mode Command is asking to start ciphering on the air, and the Ciphering Mode Complete is already sent > ciphered.
> So it might be received, but the received data may be discarded as gibberish.

In the new setup not even the Ciphering Mode Command is sent to the MS. Instead the BSC sends a Cipher Mode Reject to the MSC, if I am reading the logs correctly:

<000a> a_iface_bssap.c:629 Rx MSC DT1 BSSMAP CIPHER MODE REJECT
<000a> a_iface_bssap.c:453 BSC sends cipher mode reject (conn_id=65)
<000a> a_iface_bssap.c:457 Cause code is missing -- discarding message!
<0027> sms_queue.c:156 Sending SMS 13 failed 0 times.

The full log is attached to the issue [1].

I am setting the encryption to A5/3 in both the MSC and the BSC. A5/1 continues to work without any problems.

Thanks,
Jan


[1] https://osmocom.org/issues/3043




More information about the OpenBSC mailing list