[guardian-dev] The sound of an encrypted audio stream

[Travis Biehn]

Seriously cool Lee, I always wondered about this myself :) Thanks for
taking the time to post this.


On Tue, Jul 23, 2013 at 5:36 PM, Lee Azzarello <lee at guardianproject.info>wrote:

> I recorded the sound with a microphone. It was coming out of my
> Android device running a debug build of Linphone. I can describe the
> process to reproduce it.
>
> But now...for the TWIST!
>
> There was no human speech happening when I made this recording. No
> vowels, no consonants, no phrases. The only sound in the room was a
> fan...producing noise (though from the angle of my desk, unlikely
> white noise).
>
> There's a chance the sound was not what I thought. Perhaps it was a
> codec error, though it didn't sound like a looping buffer. I kept it
> on for over a minute. Wireshark has a bunch of VoIP protocol
> analyzers, including a utility that will try and recover an audio file
> from captured RTP packets. That'll be an interesting comparison.
>
> -lee
>
> On Tue, Jul 23, 2013 at 5:20 PM, Hans-Christoph Steiner
> <hans at guardianproject.info> wrote:
> >
> > I could also see adaptive audio filters that fill in the vowel sounds
> based on
> > the same kind of algorithm as auto-complete typing.  It could use the
> timing
> > and spectrum of the audio events as one source of information for
> filling in
> > the rest.  A decent DSP math person spending a few months on that problem
> > could make some noticeable improvements.  That bar is not very high.
> >
> > Lee, where is that sound file from?  Its pretty awesome.
> >
> > .hc
> >
> > On 07/23/2013 04:57 PM, Josh Steiner wrote:
> >> Whoa, that is way too recognizably human for comfort.  i could totally
> see
> >> with some training being able to understand that.
> >>
> >> -j
> >>
> >>
> >> On Tue, Jul 23, 2013 at 1:47 PM, Lee Azzarello <
> lee at guardianproject.info>wrote:
> >>
> >>> Hello all,
> >>>
> >>> There have been some conversations recently on IRC and on the web
> >>> about VBR audio codecs and plaintext recovery.
> >>>
> >>> It's an interesting conversation and one which will change a lot in
> >>> our times. While I was testing some video call clients, I saw a bug
> >>> between a custom build of Linphone on Android and a nightly of Jitsi
> >>> on OS X where Linphone tried to play back the encrypted audio through
> >>> the speaker without first decrypting it.
> >>>
> >>> This is what a SRTP audio stream sounds like to a wiretap. The codec
> >>> is speex at 16 kHZ, I believe it is VBR but I'm not certain.
> >>>
> >>> http://ge.tt/9FG7Tem/v/0?c
> >>>
> >>> -lee
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> >>
> >>
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> > --
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