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

[Lee Azzarello]

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
>>> _______________________________________________
>>> Guardian-dev mailing list
>>>
>>> Post: Guardian-dev at lists.mayfirst.org
>>> List info: https://lists.mayfirst.org/mailman/listinfo/guardian-dev
>>>
>>> To Unsubscribe
>>>         Send email to:  Guardian-dev-unsubscribe at lists.mayfirst.org
>>>         Or visit:
>>> https://lists.mayfirst.org/mailman/options/guardian-dev/josh%40vitriolix.com
>>>
>>> You are subscribed as: josh at vitriolix.com
>>>
>>
>>
>>
>> _______________________________________________
>> Guardian-dev mailing list
>>
>> Post: Guardian-dev at lists.mayfirst.org
>> List info: https://lists.mayfirst.org/mailman/listinfo/guardian-dev
>>
>> To Unsubscribe
>>         Send email to:  Guardian-dev-unsubscribe at lists.mayfirst.org
>>         Or visit: https://lists.mayfirst.org/mailman/options/guardian-dev/hans%40guardianproject.info
>>
>> You are subscribed as: hans at guardianproject.info
>>
>
> --
> PGP fingerprint: 5E61 C878 0F86 295C E17D  8677 9F0F E587 374B BE81
> _______________________________________________
> Guardian-dev mailing list
>
> Post: Guardian-dev at lists.mayfirst.org
> List info: https://lists.mayfirst.org/mailman/listinfo/guardian-dev
>
> To Unsubscribe
>         Send email to:  Guardian-dev-unsubscribe at lists.mayfirst.org
>         Or visit: https://lists.mayfirst.org/mailman/options/guardian-dev/lee%40guardianproject.info
>
> You are subscribed as: lee at guardianproject.info