DES ENCRYPTION TEST

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hoser
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DES ENCRYPTION TEST

Post by hoser »

Folk,

Lookin for the answer to these questions. Any input is much appreciated!


1. With the DES-XL Tx default unselected in each Trunking System, is DES-OFB then the algorithm used when the radios have the
dual-hybrid UCM with DES-XL/DES-OFB?

2. What is the cipher strength of DES-XL vs. DES-OFB? I believe DES-XL is a 56-bit cipher.

3. Which is more secure? DES-XL or DES-OFB? Why ?

4. Is there any degradation in performance using one over the other ?

5. What are the other PROS/CONS of using DES-XL vs. DES-OFB?
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apco25
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Post by apco25 »

Same encryption method, just DES-XL is for analog and DES-OFB is for digital transmissions

Otherwise the same
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batdude
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...

Post by batdude »

Same encryption method, just DES-XL is for analog and DES-OFB is for digital transmissions


actually, that statement is NOT TRUE.

i believe that this was the "way it was" according to motorola SALES upon people switching over to ASTRO from analog.

OFB is (and was) the strongest encryption available to normal everyday Moto customers - and it shares the same key length as DES/DES-XL. This is evident by the use of a T3011DX (old style) Keyloader to load both XL and OFB keys (same loader - same key can go into either an XL or an OFB slot)

i am no expert in the math used to generate the ciphers, but the key strength is the same when comparing OFB and XL.

recovered audio quality is moot as OFB CANNOT ENCRYPT ANALOG TRAFFIC

methinks this is why moto has sold so many "dual mode" DES-XL / DES-OFB secure modules.... XL for the analog side and OFB for the digital.

makes no sense really - XL is fine for both... just realize that audio quality using des-xl in analog mode sucks.... (period) and audio quality des-xl in astro mode is.... well, astro voice.

BE VERY LEERY BUYING DES-XL ONLY SECURE BOARDS (Ebay)

most of these boards have VERY old EMC revisions and WILL NOT function in newer radios.

i could continue, but i hope the above is enuf to explain what i mean.

doug
Last edited by batdude on Mon Dec 13, 2004 1:20 pm, edited 2 times in total.
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hoser
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Post by hoser »

batdude.......

Your reply intrigues me!

Especially the statement:

" recovered audio quality is moot as OFB CANNOT ENCRYPT DIGITAL TRAFFIC "

which refers to my 1st question:

"With the DES-XL Tx default unselected in each Trunking System, is DES-OFB then the algorithm used when the radios have the dual-hybrid UCM with DES-XL/DES-OFB?"

I read this as, "If you don't specify DES-XL as the Tx Default for all trunked transmissions, the DES-OFB is used" for both analog and ASTRO systems......regardless.

Is this not how to interpret it?[/img]
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batdude
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Post by batdude »

re-read the above -


it had a typo in it...


if you uncheck DES-XL transmit default, OFB will encrypt ALL your astro channels.

if you try to transmit on an ANALOG CHANNEL with OFB (i.e. the box STILL unchecked) - the radio bonks with ILLEGAL KEY



doug
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The Pager Geek
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Post by The Pager Geek »

Let's see if I can stir the pot on this again....

DES-XL vs DES-OFB
Both will encrypt digital.
Recovered audio will be the same in digital. Think about it. All the encryption is doing is coding digital signals (the converted audio to digital from the vocoder.) It's just shuffling the digital audio bits after it's been converted. On the other end, it's reversing the shuffle and sending it to the vocoder for Digital to Analog conversion.
Here's the audio path:
Microphone (analog)
Vocoder (converts to digital Astro VIA DSP)
Encryption (Merely shuffles the above data around)

Receiving radio:
Receives scrambled Astro
Astro Gets decrytped by the encryption module
Astro gets converted to Analog and out to the speaker it goes.

It's all one's and zero's unlike analog encryption. Analog encryption WAS the A/D conversion. Based on the sample rate, freq range etc, would yield your recovered audio at the other end.

Hope that clears up Digital Encrypt for now....
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apco25
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Post by apco25 »

What I meant was OFB is meant specifically for digital use, not that DES-XL is incompatiable with digital.

You guys are right :)
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Post by ASTROMODAT »

Doug said: "DES-OFB is (and was) the strongest encryption available to normal everyday Moto customers."

AES is much more secure than DES-OFB (256 bit key versus 56 bit key). And, Motorola is pushing AES hard, as it is a $600 option, while the less secure DES-OFB option is $750. More for less, so to speak.

I think Doug's point was probably that there is much more of an installed base of the old legacy DES-OFB than the relatively new AES.

Given Motorola's pricing policy, I suspect we will see a lot more AES being ordered than the legacy DES-OFB.

larry
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Post by Pj »

The catch is that most departmetns will balck at spening a whole bunch more for a new KVL when our DX loaders work just fine.

We were offered the -OFB option with our digital upgrade. We didn't for the following reasons:

Exisitng DVP-XL infrastruce using Spectra's, Sabers, XTS3000's with DVP-XL modules

Upgrade was being done over 3 years

Expense of a new KVL

My DX loader works with out X9000 all the way up to our new XTL5000's with DVP-XL installed in them. (Take that you people who want to hear our coffee orders!)

What's the REAL need? There isn't.

Unless you are a federal agency with real secuirty concerns, there isn't a real threat for day to day law enforcement to replace something that isn't truley comprimised.
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question for PJ

Post by allplowedout »

Just wondering, based on your statement of the following:
My DX loader works with out X9000 all the way up to our new XTL5000's with DVP-XL installed in them. (Take that you people who want to hear our coffee orders!)

Does that mean that a standard t3011dx kvl will load XTL and xts 5000 radios?

I thought for some reason that you needed a kvl3000 to load anything XTS.

Correct me if I'm wrong.
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Post by RESCUE161 »

My T3011DX loads my XTS5000 just fine.
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batdude
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..

Post by batdude »

the T3011 D X loader will load anything out there with DES 56bit keys, including XL, OFB and plain DES.

AES is the "gotcha" - if you want/need AES, you must upgrade to the KVL3000+



doug
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