[A51] Airprobe Decode Problems

Nicklas Boecking Nicklas_boe at web.de
Wed Oct 31 20:35:55 CET 2012


Hello List,

I work with GSM for my studies. I operate an OpenBSC Network, which can
communicate A51 encrypted with my Mobile Phones.  Goal is to find out the KC
and decrypt the call, so i can hear my own call.

 

I have got some problems with the last step. I have got the KC of my call
and can decode it with Airprobe like : "./go.sh capture.cfile 112 2t
a1s2d4f5g6h7j8k0"

In Wireshark I see all the encrypted information like all System Information
Typ 5+ 6 Messages. Airprobe leaves me a call.speech.gsm file which should
include the decrypted call.

When I convert this file into an audio  file with toast : "toast -d
speech.au.gsm" I only get some weird noises.

 

I think the KC is correct because I can display it in my Base Station
Controller and I can see the encrypted information in wireshark.

 

Are there any known problems for decrypting calls operated by OpenBSC?

Or any ideas what can cause this problem?

 

In the appendage is the Speech.au.gsm file + the output files from Airprobe.

 

Best Regards,

Nicklas

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