Re: [Openbts-discuss] "Back door in GSM"?

[Alexander C. <ale...@gm...>]

On Sun, Jan 31, 2010 at 00:32, Richard Stallman <rm...@gn...> wrote:
> Some of them could be corrected if your phone uses free software.
> For instance, you could do some sort of encryption end-to-end
> and the carrier would not have to know.

You may not be able to just encode your usual voice channel,
because network equipment expect it to be unencrypted and have
a specific format. If I understand GSM network structure correctly,
your stream may go through transcoder if called party is far enough
from you (so that it belongs to a different Base Station Controller).
If transcoder can't decode your voice data it will drop it. I think it
may work if you don't have a transcoder on your way, but that will
work on a network configuration and other factors you can't control.
I can also easily envision a system which detects encrypted
voice streams - every voice stream which has random data in it
instead of correct voice frames is likely an encrypted stream.

Other way to setup encrypted call is essentially to use GPRS/3G
and VoIP over it. But that's a different story which is not about
"fixing GSM".

But the biggest problem which you simply can't solve is that you
can't alter a way signalling is done, e.g. you can't encrypt it (or
network won't understand you). This can't be fixed without major
changes in the standard and equipment. Yet it may be a goal
for 5G, right?

> What is an "IMSI"?

International Mobile Subscriber Identity - a number which uniquely
identify every GSM subscriber in the world. It's not the same as your
phone number (which is usually unique too) and is used by network
operators internally without exposing it to public.

http://en.wikipedia.org/wiki/International_Mobile_Subscriber_Identity

-- 
Regards,
Alexander Chemeris.