Re: [Discuss-gnuradio] USRP2 + WBX for DVB-T replaying

[Marcus Müller]

> Thanks for the info
> I do need it to be real time actually
Doable.
> As for your concerns about the Emm. All I need to do is disable one not
> edit it, so it's either a re package of the steam or a jam of a specific
> header.
I understand that, but I guess you don't understand the way the multiple 
streams of data get combined in dvb-t: It's not like you tune your 
receiver to the "video channel", the "audio channel" and the "additional 
data channel"; these data streams are heavily interleaved.
You do have to deinterleave them to modify/jam only specific parts.
Then, of course, you'll need the knowledge of how an EMM actually looks
like to intercept it; and then you need to interleave it to get a 
working dvb-t transmission.
It's not like "I choose to jam frequency range x-y, therefore my card
never notices that it shouldn't decode PayTV", it needs a understanding 
of the way DVB-T transports different kinds of information, from the 
highlevel point of view of "video, audio and EMMs" down to the physical 
layer of QAM on 8096-OFDM.

I hope that helps defining the situation better.
> Can you point me to a working dvb-t project?
Uhh.. actually I'd start googling as much as you would.

Hope that helped,
Greetings,
Marcus

> Thanks again
>
>
> On Saturday, May 4, 2013, Marcus Müller wrote:
>
>     Hi Dino,
>
>     DVB-T works in the UHF / VHF frequency bands, something you can tune
>     your wbx at without problems.
>     Bandwidth is about 8MHz (if I'm not mistaken), so that's low enough.
>     Since it sounds like you'll be doing stuff offline (not in realtime),
>     processing power is not a factor for your problem, either.
>
>     DVB-T generally uses OFDM with large numbers of bins (2^11 or
>     2^13-bin fft), generous guard intervals and whatnot. A moderately
>     complex system, but someone has already implemented a dvb-t
>     modulator in GNU Radio[1], you can take a look at that, but I doubt
>     it would work with current versions of GNU Radio.
>
>     Regarding to your EMM "hint": You do have to realize that EMMs are
>     rather "high level" concepts; you need to encode them into a data
>     stream, mux them together with the video stream, encode that whole
>     thing, map it to the correct OFDM carriers and transmit that.
>     Since what we're talking about are messages meant to inform decryption
>     devices about their working state, I guess it won't be as easy as
>     replaying EMMs you captured, since it most probably carries keys for
>     specific content. Then, on the other hand, TV encryption in the 90s
>     has gained notority for being broken shortly after deployment, so
>     this is actually an interesting field of research for someone with a
>     cryptographic background (which I can't claim to have).
>
>     Happy hacking
>
>     Marcus
>
>
>     [1] PELLEGRINI, Vincenzo; BACCI, Giacomo; LUISE, Marco. Soft-dvb: A
>     fully-software gnuradio-based etsi dvb-t modulator. Proc. WSR, 2008,
>     8. Jg.
>     Am 03.05.2013 23:35, schrieb Dinos Pastos:
>
>         Hi there,
>
>         I have a USRP2 with WBX board which has been sitting around
>         doing nothing.
>         I was wondering if it is possible to use this hardware to get a live
>         DVB-T signal and replay it back.
>
>         What I want to do is to intercept entitlement management
>         messages and
>         modify/remove them on the fly.
>
>         Please let me know if there is such support with this hardware
>         or even a
>         previous project that tackles this request.
>
>         Regards
>
>         Dino
>
>
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