I have been looking into the example data provided by Osmocom as shown in the link below.

I could reproduce the first pcap output (up to the Ciphering Mode Command) for the Voice call using the gmr1_rx_live from the live branch. 

With the provided Kc, I thought I would be able to reproduce the second pcap (including the call setup). I have modified the sa_tch3.c to include the Kc code. However, I am not able to get the results as shown in the second pcap file. I noticed that in the sa_tch3.c code, there is a ciphering part (marked by "Retry with ciphering") which was disabled. This part of code didn't compile as some variables were not defined.

Probably my approach was not right. Any pointer here? Which code is needed to produce the second pcap (deciphered) file given the Kc is known?

Many thanks in advance.

Best regards,

Johann