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DES vs. DES OFB

Posted: Sat Nov 09, 2002 8:40 pm
by ASTROMODAT
Our existing UHF conventional XTS Model III portables and ASTRO Spectra mobile radios are currently running DES and are "ASTRO Ready" (analog operation). We are using RSS 6.50, and I suppose we should upgrade to the latest CPS.

We plan to FLASH upgrade to ASTRO Digital operation, and we must be APCO 25 compliant. I understand that that this will entail the Q806 and G806 FLASH upgrades, respectively (not cheap---$500 for ea XTS, and $550 for ea Spectra mobile).

I also understand that we will need to change from DES to DES-OFB, so we can run DES on ASTRO digital and be APCO/Project 25 compliant.

My question is: Must we make hardware changes? The current R3 pricebook shows a price of $749 for the XTS and $749 for Spectra DES-OFB operation. I can't tell if this means we need new encryption hardware modules, or whether we can simply (but expensively!) FLASH upgrade our existing DES hardware modules to DES-OFB. Do we need to open the radios and replace the encryption modules, or can we simply FLASH upgrade from DES to DES-OFB? We do NOT have Multikey nor OTAR options.

I assume that our T3011DX key loaders (with DES/DES XL) will NOT be able to have just a module change to DES-OFB, and we will need to go to the new KVL 3000?

Thanks, in advance, for any help on this!

Larry

Posted: Sat Nov 09, 2002 9:29 pm
by Pj
We are currently doing upgrades like you are doing, except I think we were quoted a little more from analog to IMBE.

You can use DES, DES-XL, DVP/XL etc in the ASTRO mode. It won't be APCO25 compliant, but you can use it. All the -OFB modules will do is bring your radio system into the APCO25 standard when encrypted.

You cannot FLASHupgrade the modules, but you may be able to get a trade in credit. We have DVP-XL modules, and we are sticking with them. They will work 100% in the Astro mode and in Astro encrypted mode.

Unless there is another agency that needs to transmit on your channel WITH encyption on their radio's, I wouldn't worry about it.

Again, acording to Motorola and the APCO standard, the -OFB is only required to meet the standard while transmitting encrypted.

Posted: Sun Nov 10, 2002 1:23 am
by ASTROMODAT
Thanks for the clarification and info, Pj! Makes good sense.

Larry

Re: DES vs. DES OFB

Posted: Mon Nov 11, 2002 7:30 am
by XDCLabs.COM
ASTROMODAT wrote:I assume that our T3011DX key loaders (with DES/DES XL) will NOT be able to have just a module change to DES-OFB, and we will need to go to the new KVL 3000?
Your DX KVLs will load DES-OFB keys with any changes. The same DES key can be used in CFB, XL and OFB modes. Of couse they won't interoperate, but it is the samy keying material.

Posted: Mon Nov 11, 2002 12:39 pm
by ASTROMODAT
Is it necessary that I change my encryption modules in my T3011DX keyloaders from their current DES/DES-XL to DES-OFB, so that I can load ASTRO radios with DES-OFB? If the answer is "Yes," I have never seen a DES-OFB encryption module for a T3011DX KVL.

Larry

Posted: Mon Nov 11, 2002 1:29 pm
by XDCLabs.COM
You don't have to do anything to your KVL. Both DES-XL and DES-OFB use the same DES key. XL and OFB are just different implementations of the DES algorithm and use the same type of key.

Posted: Mon Nov 11, 2002 2:32 pm
by Pj
Unless I am thinking of something else, isnt' there a DES/-XL loader and a DVP/-XL loader? I thought there were two different loaders for the two.

Posted: Mon Nov 11, 2002 6:18 pm
by ASTROMODAT
Pj, I believe you are talking about a different issue in that DES schemes use a 56 bit key, whereas DVP is a 32 bit key. So, I believe this would require a module change.

Larry