posted on Mar, 28 2010 @ 12:42 AM
In October of last year a friend and I were talking over lunch about this very issue, and we tried to figure out a way to solve the problem. We came
up with some pretty good ideas.
I didn't think any more about it until January when I'm over at his place and he hands me this little black plastic rectangular device roughly
1.5”x0.5”x0.25”. A 3.5 mm male audio connector on a short cable was coming out at one end of the device, and at the other end a female 3.5 mm
audio connector jack was mounted. On the big top surface a flush sliding switch, and on the side a USB port with a tiny micro USB stick in it. I
asked him what he handed me and he tells me it's the device we'd talked about in October. He made one for himself and one for me.
Core to the ideas we'd discussed was building a little audio scrambler that would attach inline to use with any standard headset. We'd wanted to do
everything in software, since that would be so much easier and cleaner (and anyone could install it). Hacking the audio drivers would have been
difficult and possibly ineffective, since we couldn't be sure eavesdropping couldn't happen at the hardware level. So the best solution we could
come up with was a little hardware based scrambler.
And he built it! I know almost nothing about hardware so I'd given up the idea, but my friend had been an EE in a previous career and apparently
remembered enough to pull this off. This little device he made had a programmable chip rigged to a ADC, DAC, USB port, all powered by a few button
cell batteries. I was really impressed when he told me what the USB memory stick was for. Not only did the key encryption code reside on the chip,
but it also stored data for the one time pad (OTP) he used to further secure the encryption layer.
Here's how a call worked... The audio was encrypted on the way out (microphone) and decrypted on the way in (headphones) as long as the top switch
was in the on position. If we called each other and had our scramblers attached we could just make a regular call over the cell phone network and
anyone listening in would just hear something like modem noise; his scrambler would descramble my audio and his mine. If we wanted to call a regular
person on their cell phone or landline we have to use a SIP client (software similar to Skype) on our iPhones. This SIP client is configured to route
the calls through a little software SIP gateway he placed on a server he runs overseas. He modified an existing open source SIP server to scramble
and descramble the audio in the same way that our hardware scramblers do. His SIP gateway scrambles/descrambles the audio then routes the call
through a regular thirdparty SIP network, and on to whoever I want to call. And for security he can switch SIP accounts (phone numbers) whenever he
likes.
It's quite an impressive system, but the call quality is rough! It does what he set out for it to do, but it's not the sort of thing you'd want to
use unless you were trying to communicate something sensitive. With the encryption, the latency of the foreign server, the latency of the rerouting
through the remote gateway, the latency of the thirdparty SIP network, and the layers of audio compression, the resulting audio has a painful lag and
sounds very compressed. Ah well, those aren't his fault!
To make his phone more secure he physically disabled the built in microphone on his own iPhone. I'm not as paranoid, so I left mine alone for
now.
John