[Asterisk-Users] INBAND DTMF G729 ASTERISK

[Andrew Kohlsmith]

On Friday 24 June 2005 13:10, denis at isolve.com.br wrote:
> Ok, point me on HOW may I get DTMF inband with ethereal.

You capture the data stream, then pull the audio frames out and reassemble to 
a nice slinear audio file (say wav?) -- put that through code cobbled 
together with asterisk's dsp.c or spandsp or even some already-available 
audio software and you can get data like this:

Detected tone 5
Detected tone 8
Detected tone 9
Detected tone 3
...

Hell there was a slashdot article not too far back that gave the exact 
scenario.  

Honestly it is *not* difficult, there are tools out there that do it now and 
can be put together for free. 

Yes, it's a LITTLE more difficult than just running strings over a packet 
trace, but it's not much more difficult and besides... when did script 
kiddies ever build their own tools?  They wait for someone like me to write 
it and then just download it.

> Andrew, I'm just looking for the most quality/security solution to use
> Asterisk with G729, ok?! I think this is good for all of us.

I agree.  However:

1. Inband DTMF with any compressed voice codec is flakey.
2. Inband DTMF is only slightly harder to "see" than out of band DTMF.
3. If you want voice quality you'll be using ulaw anyway.

I know what you're trying to accomplish but I'm telling you that you're 
chasing ghosts here...  all you'll end up doing is giving yourself a false 
sense of security and when someone drains your bank account you'll be 
flabbergasted because you were so certain that your DTMF was unhackable since 
it was inband, and it's simply not a valid security measure.

We're all on the same team here, I'm just trying to prevent some headaches for 
you.

-A.