COMSEC 101 – BREVMAT

I’ve been meaning to write this post for a couple of years now, and I think given current events now is the time. Today is day 27 of California’s absolutely unconstitutional COVID-19 “shelter in place” order. If we do not get this country back on track soon we are very likely to be looking at mass civil unrest.

But you are ready for that. You’ve got your rifle, plate carrier, pistol, IFAK, helmet, and you even went out and spent $1k on a Harris radio rather than a cheap baofeng. You’ve even managed to figure out how to communicate with your guys on it. And you all get yeeted by a bunch of Antifa goons on baofeng radios because they have scanners and know how to use them.

Now there are a lot of ways to mitigate that, but in my experience, old proven techniques get it done no matter what tech level you can attain. Communications Security (COMSEC) is something that very few prepper groups I’ve had contact with have actually considered, let alone have a solid plan for.

If we go down the road it looks like we’re on, I want as many good dudes as is possible to have as much of an edge as they can because it is very likely that we are all going to need it. So let’s talk about a Brevity Matrix.

Here is a sample Brevity Matrix (or BREVMAT) and I’ll walk you through what it is, how it is used, and hopefully get you thinking a little more security consciously.

Sample BREVMAT Template

This is a template for the BREVMAT I use. It’s a fantastic tool for keeping communications private, but be aware that professional intel analysts will smash this like a virgin hooker in a bar full of Marines on leave. But those Antifa guys? Not so much. Ok lets take this one block at a time.

The actual BREVMAT

This is what a filled in BREVMAT looks like. Notice that I’ve written in letters along the top and bottom where the spaces were blank. You have to fill out and disseminate a BREVMAT to your unit before you need to use it. Everyone communicating in your group should have a copy of the current BREVMAT, and the BREVMAT should be changed frequently. A lost BREVMAT should be considered complete compromise and will require a new BREVMAT be generated.

The Brevity Matrix (BREVMAT) is used to send or request relevant tactical information securely (for certain very small values of secure). The blank spaces above the matrix are used to generate secure transmission codes for this information. This BREVMAT is 6×7, so an easy solution is to use a six letter and a seven letter isogram (word that has no repeating letters). I predetermined list of these should be distributed among your unit. For this example I have used “SCALED” and “PYRAMID”. Once a code word has been used it should never be used again. Alternatively random letters can be chosen as long as they don’t repeat on the axis. When decoding, always start with the Y axis (the left side here).

In our example Bill and Ted are trying to link up:

Bill: “Ted, Bill. Charlie Romeo over.” (Hey Ted it’s Bill, where are you dude?)

Ted: “Bill, Ted. Alpha Romeo, Sierra Indigo, Charlie Mike over.” (Bill I’m at home dude, leaving now, heading south.)

Bill: “Ted, Bill. Echo Romeo, Circle K, over.” (Ted meet at the Circle K dude!)

Ted: “Bill, Ted. Lima Indigo, over.” (Bill, I’m totally on my way dude!)                                                                                                                               

While it is possible for skilled intel analysts to break BREVMATs, if codes are changed on a regular basis it is difficult. Your local OPFOR is very likely not going to be able to do it in a timeframe that matters. Most won’t have any idea what they’re even hearing.

This block is for encoding numbers. The ten letter code words (again use an isogram) will be filled in prior to OP, the numbers are counted 0-9 starting based on the date on the day of transmission. On April 6th, you would use the number row starting at 6, on the 7th, you’d switch to the row starting with 7. You write these in on the day of transmit.

Here’s how that looks for a phone number (8675309):

Bill: “Ted, Bill. I SET Bravo Hotel over.” (Ted, write this down dude! Use BLACKHORSE.)

Ted: “Bill, Ted. Copy.” (Bill, I totally have a pencil dude!)

Bill: “Ted, Bill. I SEND Alpha, Bravo, Lima, Echo, Romeo, Kilo, Charlie, over.” (Ted the number is 8675309 dude!)

Ted: “Bill, Ted. Copy over.” (Bill I totally got that dude!)

You can use any ten letters for your keywords, and any abbreviation that makes sense to you. The important thing to remember is that no keyword is ever said over the air. Never.

The idea here is to pick random words that don’t make sense in the context of what you’re talking about. I did not do a great job of that in this example. It is important not to use the phonetic alphabet for these because that leads to confusion.

This is simply a collection of words that you will use frequently in communications that you want kept private.

This should be fairly self explanatory. This is called out like so if the transmission is on the 6th of the month:

Bill: “Ted, Bill. SALUTE follows.” (I’m sending you a SPOT report dude!)

Ted: “Bill, Ted. Copy.” (Bill I’m totally ready with a pencil dude!)

Bill: Ted, Bill. Lima Yankee, Delta Delta I SET Bravo Hotel, Echo break. Setting up Jupiter, break. Squirrel, break. Alpha follows, uniform November Kilo November Oscar Whiskey November Golf Alpha November Golf, break. I SET Bravo Hotel, Hotel Echo Oscar Kilo, break. One Hammer, Four Wrenches, One Cricket. November follows. Jupiter is Charlie Mike, I am Sierra Mike to execute Mars on Jupiter from there, over.”

This is just an example of how I do it. You can totally change how you announce a SPOT report, for me this is ambiguous enough that it works.

This set is used both for sender authentication and for generating a one time pad for covering anything not in the rest of the BREVMAT. The “AUTHENTICATE” blocks are used to fill in the “I CALL” block. Notice that not all cells contain a letter. The “I CALL” block contains three pangrams (phrases that contain every letter in the English alphabet) so shorter words can be used on the Y axis (minimum of three non repeating letters), and still give you access to the entire alphabet.

The AUTHENTICATE blocks must be filled out prior to use. Here is how to authenticate traffic using these blocks:

Bill: “Ted, Bill. AUTHENTICATE BRAVO, Charlie Tango, over.” (Ted it’s me Bill, if you’re you, what letter am I thinking of?)

Ted: “Bill, Ted. I AUTHENTICATE Oscar. AUTHENTICATE ALPHA Tango Romeo, over.” (Bill, “o” it’s totally me dude! But how do I know it’s you? What letter am I thinking of?)

Bill: “Ted, Bill. I AUTHENTICATE Echo, over.” (Ted, “e” it’s totally me dude!)

Now that both parties have authenticated, take the line authentication occurred on and fill in the side and top axis on the I CALL box. The first was “DESTROY” so that goes on the Y axis, and the second authentication was “CRUMBLIEST” so that goes on the X axis. Now if these two need to say something that is not in the BREVMAT, they can do it securely:

Bill: “Ted, Bill. I CALL Delta Bravo, Delta Lima, Echo Bravo, Sierra Romeo, Delta Tango, Oscar Indigo, Tango Uniform, Delta Echo, Tango Charlie, over.”

Ted: “Bill, Ted. I CALL Sierra Sierra, Oscar Romeo, Sierra Lima, Echo Tango, break Tango Charlie, Sierra Mike, Echo Mike, Echo Uniform, Romeo Sierra, Sierra Tengo, Delta Charlie, Sierra Bravo, Romeo Uniform, Tango Charlie, over.”

If you decode that you’ll notice that there are different sets for the same letters. This makes breaking this code exponentially harder so it pays to use all ten letters. The easiest way is to pop online and grab a giant list of 10 letter isograms (are you seeing a pattern here?) and fill the AUTHENTICATE blocks with those. As with any code words, once used, those words should not be used again (at least not in the same combination). Notice in the AUTHENTICATE BRAVO block I used mostly the same words, I just misspelled them. As long as you don’t have repeating letters on the line you can also just use random letters.

There are lots of nuances that can be changed in how this is used from unit to unit so that it is even more secure. This should be part of your SOP, not the entire SOP. The biggest threat to this BREVMAT is that one of your unit is compromised or the BREVMAT is captured. Your plan must account for this. In that case you could prearrange that authenticating with for instance the letter under or over the called sequence is a distress signal and the BREVMAT should be discarded and all transmission from that source are now untrusted.

I’d like to reiterate that this WILL NOT stop intelligence professionals. This is intended to keep your communications reasonably private from casual eavesdroppers. The longer a BREVMAT is used the more likely it is to be compromised.

Stay safe out there and do everything you can to keep your privacy.

2 Responses to COMSEC 101 – BREVMAT

  1. Austin says:

    I’m a new UV-5R owner, and about to get my Technician’s license, so I’m playing with the radio.

  2. DR says:

    Would like to use this template for my group. Do you have a clean electronic file that can be edited that you could share?

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