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Re: encryption
thanks for your replies, I have to give more details

It is not analog channel . It is digital and it is not easy to access
to software/hardware , may be only to hardware that  mic-A/D conv
part.)
The device encrypts data BUT i do not trust encrypted data. becouse it
is already listened (like internet = do you trust in your IE :)
If I encrypt data in the device's microprocessor it can be recognized
or at least overwritten by an software upgrade remotely etc...

So I will add external circuit if i can.those A/D and D/A s required
for this.

Crosstalk can be a problem but how much i can not guess. i will insert
a small circuit  between mic and host A/D conv.
I am aware multiple A/Ds will generate too much noise but it is
acceptable.


voice like signal = same freq with original voice, same data dept, but
just scrambled / I will feed encrypted voice like signal into device's
A/D. I will remove the original mic/ sorry for bad english.


no need for compression,  bandwidth is ok.  voice is  8kbps\ scrambled
voice is also 8kbps \ device can send both of them without caring.


Re: encryption
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this is exactly the most complicated case. if you want the encrypted voice
to be transmitted over the same analog channel, (eg feed it into AD) then
it is VERY VERY complicated to get it done right.

in other words you can forget doing it.

--
Antti Lukats
http://www.xilant.com



Re: encryption

Antti Lukats yazdi:
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Hi Antti,

everything is naturally analog.

But I did not say the channel is analog. It is digital channel.

I use very small part of the device = just want to insert my circuit
between microphone and A/D conv.

my circuit = A/D+fpga+D/A    it seems very simple to me.

(ok I pass LNA, LPF, etc but still simple)

transmitting and receiving done by the device. every kind of noise
reduction, crosstalk issues already handled by the device.
OR do not I understand what you mean?


Re: encryption
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receiving voice converted from analog domain, encrypting in digital domain
and converting into analog domain to be transmitted over an analog channel
of the same bandwidth is not trivial at least. It is not something I would
call 'simple'. Our mileage may vary, but I doubt there are anyone who would
say 'simple' about transmitting encrypted voice over low bandwith analog
media. If you think its simple go ahead and do it. Why wasting timing
talking about something that is simple? My advice still is that it is of
such complexity that you should forget it. If you do it wrong then it will
be either not secure or not reliable. Doing it possible isnt so complex, but
being secure, reliable without quality loss or analog bandwidth increase is
REALLY complex task.

--
Antti Lukats
http://www.xilant.com








Re: encryption

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Antti,
Why can't you use this scheme? Rx voice -> digitise -> MP3 compression ->
encrypt -> a plain old 56 kbps dial-up modem ?
Cheers, Syms.



Re: encryption
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you can - but doing that with an PLD isnt something I call simple ;)


--
Antti Lukats
http://www.xilant.com



Re: encryption

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OK, I understand! And I agree. :-)
Cheers, Syms.



Re: encryption
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Don't confuse 8kHz sampling rate with 8kb/s data rate.  They are very
different concepts!

Allan


Re: encryption
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Rigth . it is just a typo .. 8x8 = 64kbps at least. thanks


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