Just slightly complicates it. All you need is for them to be in range of your catcher when they renegotiate a new TIMSI, which is done periodically. If your targeting a specific person that's as simple as deploying a catcher within range of their home and/or office and chances are good you will get most if not all TIMSI negotiations.
Like trying to stop MITM attacks on the internet by randomizing MAC addresses between sessions. IMSI are printed on a sticker stuck to the phone. How secret can it really be?
Like trying to stop MITM attacks on the internet by randomizing MAC addresses between sessions. IMSI are printed on a sticker stuck to the phone. How secret can it really be?
Even if TIMSI worked well, there are other techniques: https://arxiv.org/pdf/1607.05171.pdf