Re: [Discuss-gnuradio] Digital voice encryption block

[Marcus Müller]

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Also, if using encryption over a wireless link, you'll need some way
to ensure that damaged data gets resent, or to ensure a damaged block
does not affect the decryptability of following data.

So I think your flowgraphs should read

Mic/Soundcard -> low pass -> source coding (at least some uLaw or so)
- -> encryption -> frame building & channel coding -> symbol
mapping/modulation -> pulse shaping -> tx system

rx system -> freq/time/clock sync (might include deframing) -> channel
decoding (equalizing might happen somewhere here) -> decryption ->
source decode -> soundcard

As Sean pointed out, this does not necessarily translate nicely into a
GNU Radio sample flow graph and you might be better of with a
combination of sample flows and message passing.

With encryption, you really really need the channel code, since a
single flipped bit will render your transmission unusable.

Also, I don't really understand: GRC creates python *flow graphs* out
of graphical representations. It can generate hier blocks, which are
just flow sub-graphs internally, but it can not generate blocks that
have a work function.

If you're already at ease with designing oot modules, then using a
python library to encode a block of data seems to be rather trivial,
and I don't see how that should be possible or easier from withing GRC ;)

Greetings,
Marcus


On 17.04.2014 16:37, Ralph A. Schmid, dk5ras wrote:
> Question 3: AES is indeed a common system for voice encryption,
> widely used for example in US police / public safety radios (APCO25
> standard). Older systems used often DES, but not with a neat linear
> predictive voice codec, but just a CVSD digitizer, DES box and FSK
> radio link (Motorola SECURENET). Then there are lots of proprietary
> / closed source encryption systems, some really weak with 32 bit
> keys, more aimed against the casual listener / scanner kid, but not
> providing real security against an advanced eavesdropping attack.
> 
> 
> 
> Ralph.
> 
> 
> 
> From: address@hidden 
> [mailto:address@hidden On
> Behalf Of Tigor Christian Sent: Thursday, April 17, 2014 3:50 PM 
> To: address@hidden Subject: [Discuss-gnuradio] Digital
> voice encryption block
> 
> 
> 
> Hi all,
> 
> 
> 
> I want to simulate a voice transmission system in GNURadio
> Companion (GRC) before I build a real one. My system configuration
> is as follows.
> 
> 
> 
> TX:
> 
> mic --> encoder --> encryption --> modulator --> RF
> 
> 
> 
> Rx:
> 
> speaker <-- decoder <-- decryption <-- demodulator <-- RF
> 
> I have succeed in simulating the above configuration in Ubuntu
> 12.04 LTS machine but without encryption/decryption blocks.
> 
> I want to encrypt my digital voice using AES (128/192/256, either
> one) algorithm, but so far, I couldn't find suitable blocks for my
> purpose.
> 
> I know that GNURadio will synthesize a python code when you compile
> your blocks configuration in GRC. On the other hand, every python
> dev installation in Ubuntu will also install PyCrypto lib in your
> machine, this library has a ready-to-use function of AES algorithm.
> Furthermore, I also know the concept of Out-of-Tree Module (OoTM)
> of GNURadio.
> 
> My questions are:
> 
> 1. My first thought is to get data stream of certain block and do
> encryption process with PyCrypto (not in the OoTM, but directly in
> synthesized python code) then put them back to the next block.
> Would it be possible and how to achieve this?
> 
> 2. Do GNURadio has a ready-to-use GRC blocks or OoTM of digital
> encryption algorithm (not scrambler)? and how do I get it (a
> tutorial would be fine)? So far, I can not found the block either
> in GRC or https://www.cgran.org <https://www.cgran.org/>
> 
> 3. Last question may be off topic a bit. Is it common to use AES
> algorithm to encrypt voice data, or is there any common encryption
> method (preferably could be implemented in GRC)?
> 
> Thank you for your time and willingness to answer these questions
> 
> Regards tc
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> _______________________________________________ Discuss-gnuradio
> mailing list address@hidden 
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> 
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