[asterisk-biz] Encrypted calls between mobile gsm and isdn (asterisk)

[Alex Balashov]

I'm pretty sure if you quantise it (modem-style) and turn it into data 
you can apply as strong crypto as you want, and then convert it back to 
analog.

The main issue would be the bandwidth available and quality, me thinks. 
  The 3.1 KHz PCM acoustic bearer spectrum of the PSTN is a well-known 
problem that limits modems to speeds like... < 56k.  And that's with one 
side of the loop being digital;  less if it's analog end-to-end.  Not 
exactly voice-grade.

On 02/25/2010 08:46 AM, Trixter aka Bret McDanel wrote:

> On Thu, 2010-02-25 at 08:25 -0500, Alex Balashov wrote:
>> Although, acoustic coupling-based encryption would be kind of nifty...
>> surely exists in the government sector.
>
>
> how I have done that is to encrypt via a data call which means that you
> can decode that data bit for bit on the pstn so it works that way.  This
> works even if the call goes over the pstn since the pstn call is also a
> data call the same as gsm to gsm.  Further, it is not limited to gsm (I
> havent implemented it on a phone that is something else) since you only
> need a data call to implement it on other phone technologies.
>
> I have used two ciphers though so if one is broken you are still
> somewhat safe.  aes256 and blowfish both as a stream cipher.  To crack
> it requires that you break both ciphers.  There is also a hash available
> so that you can ensure that there is no MITM game going on, although
> that is less than useful if you are calling an IVR.  I started to
> implement tls to verify the other end, but got bored and distracted and
> never finished that part of it.  For the IVR side you need to have
> certificates issued (which can be self issued if you want to be the CA)
> which replaces the hashing system mentioned above.
>
> At one point I was looking for someone to sponsor this, no one came
> forward so I kinda set it aside for now.
>
>


-- 
Alex Balashov - Principal
Evariste Systems LLC

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