[MRCG] field day crypto

[Mark J. Blair]

On Jul 28, 2013, at 07:45 , Jason W6IEE <w6iee.73 at gmail.com> wrote:

> "Does anybody else want to play with crypto at this Ft Mac event?"
> 
> Sure, but how do we get away with it, rules and all?

There are a number of ways we can play with crypto while complying with part 97 rules.

* Don't transmit the ciphertext at all: Vintage military vehicles are often involved in our Ft Mac exercises, so sending ciphertext by courier is an option. A courier might bring a ciphertext message to a field station to be deciphered and then transmitted in cleartext, responded to in the clear, etc. Or a field station might encipher a message based on observations or received messages, and then courier it back to net control at the end of the event.

* Transmit outside of ham bands, when a legal option is available: As part of our big annual meet in San Luis Obispo last May, maritime historical station KSM transmitted ciphertext on their licensed commercial frequencies via CW and RTTY. We received and deciphered the messages at SLO, and other non-MRCG-afiliated participants also joined in on the fun. See more here:

    http://www.nf6x.net/2013/04/ksm-mrcg-joint-crypto-operation/
    http://www.nf6x.net/2013/05/2013-mrcg-event-after-action-report/

* Operate part 15 instead of part 97: I don't think we've done much if anything with this approach yet, but one option for localized events would be to transmit at low enough ERP to fall under part 15 rules. This is an option that Bart WB6HQK (SK) and I discussed for use at SLO events. He calculated that a GRC-109 with a dummy load and short piece of wire radiating element would fall under part 15 rules, and should be receivable throughout the NCO club and RV park area. This option might be especially fun once one of us implements a practical way to decode received GRA-71 code bursts!

* Don't obscure anything: If I understand part 97 correctly, the restriction isn't so much on use of crypto as it is on obscuring information. If we transmit both plain text and cipher text of the same message, then nothing is obscured. I think it should similarly be Ok to transmit, in the clear, that the following message will be enciphered with method X and key Y (possibly by providing a web page address with information about deciphering the message and/or the plaintext of the transmitter message). I believe this would comply with the letter and spirit of the law.


At the very least, I'll bring along my M-209 on the 17th so I can train up the other MRCG member who recently acquired an M-209, as well as anybody else who is interested. I may or may not come up with some scheme to incorporate M-209 use into the on-the-air/in-the-field activities for this event, but I can lead an impromptu round-table talk about crypto for anybody who's interested.


-- 
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/