[asterisk-dev] GSM Encryption

[James Sharp]

On 10/28/2012 4:33 PM, sab sab wrote:
> 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
> http://www2.rohde-schwarz.com/file_1464/Top-Sec_en.pdf

I suspect it works just like any other telephony encryption system.

You place a regular call from your crypto capable handset to a crypto 
capable destination.  You speak for a bit and then "go secure".

When you kick the system into secure mode, the mic and speaker are 
disconnected from the phone's audio path and the phone sets up a low 
bitrate modem call between the crypto chip in the phone and the crypto 
chip in the destination unit.  The mic and speaker are connected to the 
crypto chip and the audio is encrypted and then sent over that low rate 
modem call, at the expense of significant audio quality.