encryption

hi,

I would like to implement a secure channel over an unsecure medium.

mic(voice) => A/D conv =>digital, unsecure, unknown comm link => D/A conv =>voice analog Host A/D digital "other side"

I do not want to encrypt data at the device's digital side because it is unsecure, and I dont know how to interfere digital data I don not have access to embedded software, source code etc. (maybe just after host A/D converter and emulating Host A/D converter to device,,,maybe) and every encryption algorithm implemented here can be broken at the other side I guess.

What I want to do is ;

mic(voice) => A/D conv + cpld or fpga + D/A conv =>A/D conv => unknown comm link analog ecrypt + scramble digital data voice like encrypted signal

The Device will see voice freq signal and will transmit them through channel as if they are real voices. At this point adding some noise may help a lot. a little bit noise may fool attackers but human still can understand what is said.

questions:

what is possible weakness of this system? I am sure it can be still broken but how easy to break it? What kind of tools/approaches "they" are using ? Is cpld enough for general data encryption? (data is human voice so 8Kbps.) encrytion should be easy so the hacking also.... they: whatever you say

thanks

yusuf

Reply to
yusufilker
Loading thread data ...

I forgot to tell. Of course at the other side of the link there will be a decryption unit to convert analog encrypted voice into real voice.

Due to word wrap some text are not aligned in previous post . sorry..

yusuf

Reply to
yusufilker

Such scrambling may produce a lot of higher frequencies which after being filtered out by the equipment and the line result in data loss.

Rene

Reply to
Rene Tschaggelar

This would be the minimum required to make a "professional-grade" voice encryptor:

mic => ADC => compress => encrypt => frame =+ | modem comm link | spkr

Reply to
allanherriman

Howdy yusuf, see below...

Why do you think it is unsecure? Hopefully a professor isn't telling you that, as I believe it's how most governmental and non-governmental encryption is done.

What makes you say that "every encryption algorithm implemented here can be broken at the other side"? Why is it easy to break "here" and not somewhere else?

I'm not sure what a "voice like" encrypted signal would be, but I'm pretty sure that if someone could tell that it was voice like, it will not be secure. I'm also not sure what the purpose of all the A/D's and D/A's are, but that's a side issue that doesn't seem important to the rest of the discussion, so I'll just skip it.

I believe that adding randomness (noise) to the input signal/data that is about to be encrypted is bordering on security by obscurity, which in theory, adds little to no real protection to a determined attacker. In practice, you might be able to argue otherwise (maybe that every little bit of security helps?) - but know that modern cryptographers like to rely one thing and one thing only: the length of the key. They typically use algorithms that are known and respected industry wide. They use algorithms that have been peer reviewed many times over many years.

With absolutely no disrespect intended, if you don't know what the strengths or weaknesses are of a system you are trying to design, or what kind of attackes someone might make on it, I'm afraid that a Usenet posting or two probably isn't going to help (even if it were from an experienced cryptographer, which I'm not).

Compressing human voice down to 8 kbit/s requires a little bit of horsepower. It would not surprise me if it was beyond the capabilities of a CPLD, or if it is possible, would require an experienced coder that is very efficient in how they implement algorithms.

Have fun,

Marc

Reply to
Marc Randolph

On a sunny day (25 Jan 2006 04:20:40 -0800) it happened snipped-for-privacy@hotmail.com wrote in :

Do not forget the anti-aliasing lowpass before the ADC.

Reply to
Jan Panteltje

Transmitting encrypted voice over band-limited analog link is VERY VERY complicated task. If you want secure and reliable connection over analog link that does not reduce the quality (eg provides almost the same bandwidth as clear channel) then calculate at least one man-year development time. Probably more.

I have hacked an secured digital sound transmittion standard once a long time ago. It is amazing what has to be done to digitized voice in order to hide its nature of being voice data. Anything that is from our world eg sound, voice, captured image keeps its characteristics after large amount of distortion applied, things like bit swapping/interleaving, xor patterns do not change almost anything - methods exist to recover the original.

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

Although, I think I could get a Linux box with a sound card and a modem to send an encrypted MP3 compressed stream over POTS in a lot less than a year. Cheap too! You could use ssh and send it over the internet. Perhaps you could run Linux on the FPGA's PowerPC? Cheers, Syms.

Reply to
Symon

And the low noise preamp, and the low pass filter and power amp for the speaker, and the DSP-based acoustic echo cancellation, and the analog noise generator (for the keys) and the controlling microprocessor (if not using the DSP chip for this) and the power supply components, and ... and ... and.

Naturally, one leaves out some irrelevant details.

Regards, Allan P.S. how did you know it was a sunny day here?

Reply to
allanherriman

Obviously, if a design uses poor crypto, then it can be cracked without too much diffculty. Even "good" crypto (e.g. AES) can be misused. It's quite hard to get right in practice.

I rather like the wikipedia entry on Block Cypher modes of operation that shows a striking flaw in ECB.

formatting link

I'm guessing that CTR mode would suit the OP's application.

Regards, Allan

Reply to
allanherriman

He's obviously been following the cricket now that Holland have qualified for the world cup. It looks sunny at the SCG in the picture of Jayasuriya after he hit a century!

formatting link
Cheers, Syms.

Reply to
Symon

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.

Reply to
yusufilker

schrieb im Newsbeitrag news: snipped-for-privacy@z14g2000cwz.googlegroups.com...

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
Reply to
Antti Lukats

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

Allan

Reply to
allanherriman

On a sunny day (25 Jan 2006 05:28:15 -0800) it happened snipped-for-privacy@hotmail.com wrote in :

So tha twas not very professional, as i tshows no knowledge of signal processing.

I only know you reply to me because of the headers, you forgot to qute what and who you are replying to. Not very professional either.

As for the sunny day, try a suitable reference frame.

Reply to
Jan Panteltje

Antti Lukats yazdi:

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?

Reply to
yusufilker

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

Reply to
yusufilker

snipped-for-privacy@hotmail.com yazdi:

Device has its own speaker (and related dsp functions, power, power amp etc). LNA, analog LPF, no need to control it is freee running continuous process. How to enter encryption keys still thinking about it..

Reply to
yusufilker

schrieb im Newsbeitrag news: snipped-for-privacy@g43g2000cwa.googlegroups.com...

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
Reply to
Antti Lukats

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

Reply to
Symon

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