[asterisk-dev] GSM Encryption

[Benny Amorsen]

sab sab <sabin_098765 at yahoo.com> writes:

> Thank you. It's sad because you may have killed a dream. But there is
> still some hope. Can anyone tell me how did they manage to pull it off
> [1]http://www2.rohde-schwarz.com/file_1464/Top-Sec_en.pdf

"Encrypted speech is transmitted on the transparent GSM data channel."

In my reading that means it uses circuit switched data, probably just 1
timeslot so 9600bps. They also say they use a half-rate GSM codec, which
would fit in 9600bps. "Excellent voice quality" is certainly a lie for
that codec, it sounds awful.

If providers still support circuit switched data at all these days, they
almost certainly support HSCSD, so you probably have up to 57600bps to
play with (if you can afford the call charges).

Now that I think about it, all those GSM credit card terminals are
likely to be using (HS)CSD. I bet it still works with most plain GSM
providers at least.

I would still recommend GPRS. It is a lot cheaper and you get a lot more
bandwidth to play with. Latency is unreasonable, which can be a problem;
HSCSD latency is much better.


/Benny