This subject is a much overlooked area in the survival community and sorely neglected. I hope that the following synopses of this crucial topic will inspire an invigorating awakening in this area that I feel is vital to our collective success, without which our endeavor could well be doomed.
Every country and every military around the world through the ages has employed codes, ciphers and signals as well as signets et cetera for security and authentication of messages. Sending messages via couriers, as well as during times of war and peacetime to prevent their opposition from learning their secrets and their plans. They are crucial to any groups survival and successful operations especially in matters of cover and concealment which is of utmost importance to the modern prepper/survivalist who wishes to successfully maintain operational OPSEC as well as communications security (COMSEC.)
Most apropos to the survivalist is the aspect of camp security or camp entry codes in the ares of individuals securely moving in and out of camp as well as moving securely between friendly camps as well as sending and receiving light or radio signals to members of ones own camp such as in the area of LP/OPs (listening post-observation post) and in communicating with other friendly camps to coordinate movements and plans as well as advise other of enemy actions including METT-C. and size activity location unit/uniform time and equipment (SALUTE) reports. Not to mention something as basic as your challenge and passwords.
Sadly, few have planned, employed or even consider training in the area of signal security by broadcasting encoded Morse messages which is imperative to any group's survival in hostile territory, especially given this governments stated goals as well as those it consorts with! These transmissions must be made carefully and remote from camp and kept very short...preferably in burst format which the receiver can then electronically slows down to decode. This is only limited by your means and available equipment. You then establish an radio telephone operator (RTO) who would manage all frequencies, call signs master CEOIs, et cetera. Each member of the group should have a specialty, much like a Military Occupational Specialty (MOS) while all members training in and being proficient in basic skills while having a working knowledge of all other in the event that person is lost.)
These signals not only encompass light and radio but human-- for instance a messenger who carries a memorized message encoded or sends them via light or hand signals or in the form of hand gestures to form near and far signals, again for the purposes of camp entry codes. Or he or she may be carrying hidden messages. Thee can include embedded distress signals therein in the event one is captured or compromised so that those within the camp can know that there has been a compromise. These signals/signs should be relatively simple while unique to that group but have alternate but subtle variations in the event one is being forced to do harm.
More sadly, we now live in a formerly free constitutional republic. The reality is we now live in a soviet style clandestine environment where we can only speak openly and freely to our most trusted friends and family weather face to face or on the phone or on a computer.
There are many forms of code/cipher that have been employed by all the various governments and their militaries. For instance in the 19th and 20th Centuries there was the Pigpen cipher, Play Fair (used by the Australians), and the rail fence cipher. These are just a step up from simple substitution codes, and only a bit more secure--they can be broken fairly easily. When I taught my church's and survival groups codes I would give them a breakdown of a few as here and then tell them that of course the best code is the code you conceive and employ yourself. I am not going to disclose the exact nature of our code of which I made copies and distributed. In that I have devised a combination of the military's brevity codes (which are pretty much unbreakable unless the source is known or there is repetition) as well as substitution codes embedded with Morse code, possibly in different languages common to a group.
We had a lot of fun breaking into groups and I would give them brief messages to encode and decode using just the angle head flashlight....of course informing them that once you know a form of Morse you can send it in many ways including light, radio dits and dahs and finger and motions as well as written cipher in that way. You are already familiar with certain subversives who employ such "close signals" for instance the Masons who use a variety of hands signals and shakes to identify one another and their condition as well as the dizzying array of miscreant gangs who use hand signals to ident one another and their misguided loyalties.
One brief aside: it is noteworthy to mention that as well the military are using infrared tabs on their ACUs so that from afar in their night vision scopes they can discern friend and foe. Something to bear in mind!
So I will begin with the Morse code aspect of the encryption, every country has their own and their is a international code which is very close to ours. I have created Morse in a few different languages and keep them in sort of a S1 CEOI format, so that if one code or messenger is known to be or thought to be captured or compromised then you just break into the next set. (Such as Spanish or French whatever you are familiar with or not at all. Now, after mastering your Morse code skills in sending and receiving which is best accomplished by learning them in rhythm. You then break them down to 3 character codes. You might for example take a foreign language dictionary and start at the first word in its columns and start designating every word or field appropriate word if you prefer a 3 letter designation. This can be done in an English dictionary but if so you will not want to do so alphabetically as it could then easily be deciphered if you do not then combine the traits of shift code (of which there are several). E.g., If you want to start left to right as is done here and everywhere west of Israel...you can start at the beginning of the alphabet and skip say...three letters so that a becomes c. Or you could Start counting right to left as the original Bible does and shift that direction by a pre-designated number. You could choose this number by the day of the week, so if the code was sent on Sunday, and by the definition of the dictionary that is the 1st day of the week then it would be known to your group and allies to shift left by one. The shift could then or also be know to be shifted by a word or name. There is a near infinite series of alterations that a group could use to confound the enemy cryptologist (code breaker.)
Okay, so starting again in your dictionary of choice-preferably a concise one that would easily fit in your ALICE pack or go bag but even better in your BDUs, and of course whomever you are sending or receiving from would have to have a duplicate set to decode from. If you choose in your system, you can start at the beginning starting with aaa and let's say hypothetically that the first word in your foreign language dictionary means about so aaa is the 3 letter morse code designation for about, then the next word in your dictionary would be designated aab and the next aac etc., etc.. Now obviously your names/call signs and other words particular to your group and objectives might not be in a or that dictionary....so then you would create your own addendum where you would assign all members of your group their own 3 letter designations as well as say particular weapons or names of enemies or other actions for the purposes of brevity rather than having to scroll through the dictionary to find a particular word which is peculiar to you and your groups actions. So a 6 word message might look like this:jeb ofn pje suc jeu bhe and you may transmit them together and it be known to break them up in triads as such, jebofnpjesucjeubhe and that message might mean in your code: for enemy has captured friendly forces rally3.
Now, as you see "rally3" is not one word, in fact any 3 letter brevity code can not only represent one word but a phrase or direction such as proceed north or reinforce at 1200 hrs for example. This is why brevity codes combined in morse code configured with alpha/numeric shift is so valuable a cipher.And as you see I am only giving you a pattern in which to create your own without compromising mine! Now...once you and your group establish a platform to create your own cipher you then complete what is called a CEOI or "communications electronic operating instructions" card and make copies for your people. These cards must be laminated to be made waterproof, all team leaders and above having detailed copies while the individuals only needing condensed versions.This will serve as a baseline for you to create and employ your system in such a way that the enemy even if they capture you cannot necessarily break your code. You do this as you create your own computer passwords. This is something that is familiar to your group or established but in a regimented fashion. You should then create a system in your CEOI wher all your members names/call signs are encoded as well as a basic group of commands such as camp entry/denial codes as well as protocol for how to deal with stress signals and challenge pass words, remember it is your prerogative for these codes to move left right or vice versa! Or even up and down etc.,. In that you can employ colors or animals as authentication codes for each day of the week which may change for each week of the month...be creative!
We have covered signal security some in that those codes covered mostly some visual or radio signals now we can address some simple hand signals for CLOSE friend-or-foe or identification hand signals. Now...again...we have our established signals but for purposes of OpSec I will not give my examples. But again invite you to be creative and invent your own. As I alluded earlier as the decadent groups have their hand signals (which underlie their loyalties,) so do we. Now...it is for us to again be creative and establishing some group standards but also create alternatives in the inevitable event that one of our own is compromised and provide for that in the system! In addition to employing hand signals for signaling and identification. I notice that everyone is sorely lacking in their hand signals for moving as a unit or units in the field. This is underestimated as a prerequisite for successful movement and maneuvering bearing noise discipline in mind. Of course there are the pretty much standard hand signals for rally on me. Halt, danger I see...but what about formations such as traveling wedge formation and moving in bounds/bounding overwatch. There are standard signals for these as well that a leader should learn, master and impart to his or her group. But then what many may overlook is ammo count. When engaged or pinned down and the enemy is trying to outmaneuver your people need to be able to effectively communicate who has how much ammo. The team leader for instance using this signal could then decide who has suppressive fire abilities while another can take well aimed shots to end the action. For this I use an extended hand with fingers straight out and rotate 90 degrees twice indicating an ammo count. The response from members should or could be that of standard deaf signing numbers which all members should be savvy with anyway in indicating numbers.
Distant identification which is predicated upon environmental considerations, that is, how dense or sparse the vegetation is in your area of operations (A.O.) limiting visibility. So, if visibility of your observation post listening post (LP/OP) is a maximum of 100 yards, then that range should be considered your "long range signal." and perhaps then 50 yards would be your established "close range signal range." Now, at 100 yards small details of hand or arm motion may be confused so you want large pronounced movements that are not easily confused as your "challenge" arm signals. So you may want to employ a large circular movement mimicking the hands of a clock yet distinctive and these may again be tailored to the days of the week so that if an enemy observer is watching one day or so he may not easily determine what that long range signal is and counterfeit it to gain access to your camps mid range security threshold. So...let's say your challenge signal for Tuesday is palm out and one full circle outward or clockwise to the challengers perspective and the passwords long range signal response is the left arm beginning at the upward 12 o'clock position moving to the 180 degree downward then palm to center and across the chest. Permission is then granted to proceed to the close signal where closer observation can be made to positively ident the incoming party. When the incoming party advances to the close signal range,they are instructed to halt at which time the close hand signals are exchanged. This may be as simple as a particular hand sign as the gangs and Masons are notorious for, such as the deaf hand symbol for the 4th day of the week or the phase of the moon being between 1 and 5 or even a smaller arm signal recognized by the groups in that Area of operation which of course includes distress/"I am compromised" signals in which the camp would be alerted that an attack is imminent. They are then directed to advance to be recognized and asked the verbal challenge and password. If all signals are within code parameters and given a small degree of variance for error...up to the verbal challenge....then the incoming party may enter upon authorization of the s1 intelligence officer of the group, In other words. the person responsible for devising and maintain all codes/ciphers and challenge passwords which all teams including the foragers, hunters, water gatherers and security or LP/OP teams must be drilled on for camp security!
The foregoing dealt with daytime signals. The same would be true of night time operations except you would want to use a subdued light source such as the common angle head flashlight with filtered lenses. A red lens is optimal, blue under certain conditions but that is mostly just for map reading. Now I have devised ways of covering the lenses so that they are half and half, that is: half the lens is red and half blue and another is half purple being a combination of red and blue and the other a red hemisphere. I provided these for my group along with a camp entry code card sort of a mini CEOI. I also created these light signal cards for camp entry codes with my particular signaling devises in mind and distributed to critical members of my group. In this way when the situation goes hot and we invariably find ourselves struggling to rally to our pre-designated points etc.. We can then safely regroup at a future point without being compromised by those whose charge it is to pick up as they say in the military police field manuals distributed to the various defense force people for instance "stragglers."
I also created similar waterproof cards demonstrating various hand and arm signals for this purpose...I sewed an extra pocket into my uniform to accommodate this information and waterproofed it inside and out as well. If you do not have angle head flashlights such as the GI issue, you can fashion you own favorite flashlight using red taillight repair tape. The Mini-MagLites are good and you can buy tail cap switch kits for them that allow you to tap out Morse code from the butt of the light. In my large angle head as well as the smaller ones I use rechargeable batteries. The D size rechargeables are immensely lighter. I use the solar powered battery charger to recharge them.
One last note on the use of brevity codes and your challenge and passwords. You can even use your 3 character brevity codes to designate a challenge and another for your password. Be creative have fun and get going cause the balloon is going up!
JWR Adds: As a former Army ASA SIGINTer with some cryptological experience I must warn readers that the foregoing simple ciphers are no match for any modern military or government intelligence organization. They would be able to fairly easily and quickly decrypt your signals, given a sample of sufficient length. However, it should work fine if your opponents don't have any greater sophistication than the average outlaw biker gang. Something as simple as a traditional Play Fair or Four Square code would likely confound them.
Some advice: Never re-use brevity codes. Change your codes frequently. Keep transmissions short and use the minimum power to get your signal through. And remember that even if you use strong encryption, most radio transmissions can be quickly located via radio direction finding.