Communications is a key element in our everyday lives. If you don’t believe me, try going a whole day with no cell phone, Internet, television, or any other means of communications (COMMS). So it stands to reason that having COMMS, when SHTF, is essential to gaining intelligence (COMINT), the safety and security of your family, keeping informed, and keeping at least one step ahead of anybody with bad intentions. Like any skill, it is essential to practice; that means practicing before SHTF, so that you have the necessary skills. While most of the communications methods discussed in this article are in plain language, rather than in code or encrypted, because the day-today rules do not allow the use of codes, there are some methods for disguising the meaning that can be practiced. This article will provide information on various means, methods, and devices for COMMS, as well as communications security (COMSEC), for SHTF scenarios. This article cites the various rules that apply to the different radio services. The application of the rules in normal times is strongly encouraged so that you do not draw attention to yourself from the authorities. Application of the rules when SHTF, well …
Some Basic Terms
Frequencies
First, let’s understand a little about frequencies, their uses, and their availability to the average person. The use of frequencies in the U.S. is governed by the Federal Communications Commission (FCC). Some frequencies require a license, and some are licensed by rule, meaning that the rules provide the allowable use without an individual license, such as Citizens Band (CB) and Family Radio Service (FRS). Other services, such as Amateur Radio (HAM) and General Mobile Radio Service (GMRS), require an individual to have a license. Each licensed service has specific rules for use, and radios designed for use within a specific service have to be type accepted for use in that service. A channel is a “common” name for a frequency, or pair of frequencies, pre-assigned, such as CB channel 19, which is a single frequency. Where a single frequency is used, it is called simplex. When a pair of frequencies is used, one is used for transmitting and one for receiving; this is called duplex.
Bands
Radio frequencies cover a whole spectrum. They are broken down into bands, with each band having different characteristics. Low bands, (high frequency “HF”) are also known as short wave. They tend to bounce off the atmosphere and, therefore, are good for long transmissions around the world. Because they bounce, places between the transmission point and reception point cannot hear the transmissions very well, if at all. This has obvious advantages to COMSEC, but it can be a disadvantage when attempting to communicate locally. The time of day and even time of year change the characteristics of HF bands. The low bands, 160 meters (1.8-2khz) are good at night but are almost unusable during the day. This band is similar to the long distance AM stations and is better during the winter, with transmissions possible over thousands of miles. Whereas 10 meters (28Mhz-30Mhz) is best during the day. Some bands between these (such as 17, 20, and 40 meters) are good during the day and into the evenings. Transmissions in the VHF and UHF bands are considered “line-of-sight”, as they travel in almost straight lines and, therefore, do not follow the curve of the earth. We usually refer to these as tactical COMMS. Terrain, like hills, can block transmissions in the UHF and VHF range. Tactical COMMS equipment tends to be smaller and lower in power. “Line of sight” transmissions can be easily intercepted with direction finding equipment. (“DF’d” or “DF’ing” is the art of direction finding.) For a good description of band characteristics, go to http://www.hamuniverse.com or http://www.w5yi.org/downloads/FreqChart.pdf, which shows the Amateur Radio band plan as well as which HF band is best during different times of the day.
Selecting the most appropriate band for the type of COMMS is essential. Selecting the lowest possible power to get the message through and making transmissions very short helps prevent “DF’ing”.
To convert frequency (in Mhz) to band (in meters) divide 300 by frequency (in Mhz) i.e., 300/440Mhz = 0.68meters, usually called the 70cm band in Amateur Radio. To convert the band (in meters) to frequency (in Mhz) divide 300 by the frequency i.e., 300/2 meters = 150Mhz
Continuous Tone-Coded Squelch System (CTCSS)
CTCSS is a sub-audible tone that can be added to a frequency to help reduce interference from other users of the frequency. In most cases, it is used to eliminate interference getting into a repeater system. CTCSS is also know by vendor names such as Private Line or PL tone by Motorola, Channel Guard by both Bendix King and GE, Quiet Talk by Kenwood, and Tone Guard (TG) or CallGuard (CG) by EF Johnson. Generally, in “radio speak”, the generic term “tone” is used.
There is an industry standard list of tones. In most cases the actual number of the frequency is listed, i.e., 127.3, or a two-character code utilized by Motorola, such as 3Z (for 127.3). The use of tones does not provide any security on a channel. In “bubble-pack” radios– typically FRS radios– the vendors assign a number (not the actual frequency) to a tone; these are not consistent between different manufacturers.
Digital Coded Squelch (DCS)
DCS is a digital version of CTCSS that puts a continuous stream of digital data on the transmitted signal. As with CTSCC the different vendors have their own names. Motorola calls it Digital Private Line (DPL); GE uses Digital Channel Guard (DCG); and Icom uses Digital Tone Squelch (DCS).
Repeater
A repeater is basically two radios– one on a receiving frequency and one on a transmitting frequency. The user radio transmits on the repeater’s receive, or input, frequency, and the repeater re-transmits on the output frequency. Typically a repeater is located on a hill top or a high building. A low-power radio is then “repeated” on the higher power, or at least higher antenna, of the repeater and can be heard over a considerable distance. Depending on the location and frequency, this can be as much as 50 miles.
Spread Spectrum
This is a technique where the signal is spread over a wider bandwidth. This reduces interference from jamming, which is the ability to be intercepted or the transmitter to be DF’d.
Frequency Hopping
This is where the radio signal “hops” between different frequencies in a pseudo-random pattern, known only to the radios. Again this makes the signal difficult to intercept (or DF) and is, therefore, good COMSEC. Some equipment incorporates spread spectrum frequency hopping techniques. Unfortunately, this equipment can be expensive.
Automatic Link Establishment (ALE)
ALE is a feature of some radios that enables them to automatically find the best frequency for the transmission. The radio can be programmed to scan a number of different frequencies in different HF bands. When one user wishes to communicate with another, the user selects the ID for the other radio; the radio then determines the best frequencies and “calls” the other radio. Many Federal agencies share the Customs Over the Horizon Enforcement Network (COTHEN), using radios with ALE built-in to the radio. Meanwhile, the Amateur Radio service operates ALE with both voice and data channels, using computer software interfaced with HF radios. (See hflink.com for more information.)
Licensed By Rule Services
Licensed by rule services do not require the individual user to have a FCC-issued license.
Family Radio Service (FRS)
The Family Radio Service is a “licensed by rule” service, under Title 47 Code of Federal Regulations (CRF) Part 95 subsection B. The FRS is 14 frequencies in the UHF range with a power limit of 500mW and 11.25khz spacing of the frequencies. This limits their range to about ¼ mile or possibly up to one mile, depending on terrain. A more unobstructed terrain permits greater distance. FRS radios list the channels by channel number, and all vendors follow the standard labeling of the channels. Different manufactures make their radios available in differing CTCSS capabilities, usually listing them by a number that does not correspond to the actual tone. Unfortunately, the vendors do not all use the same tones or numbering system, which can make communicating between different vendors’ radios a little difficult. FRS radios are sometimes referred to as “bubble-pack” radios, due to their packaging in stores. One of the rules for type acceptance of FRS radios is that they cannot have detachable antennas, thus they cannot be connected to an external antenna, such as one mounted up high, to increase the range. Most FRS radios run on AA or AAA batteries. The FRS channels and frequencies are:
FRS 1 462.5625
FRS 2 462.5875
FRS 3 462.6125
FRS 4 462.6375
FRS 5 462.6625
FRS 6 462.6875
FRS 7 462.7125
FRS 8 467.5625
FRS 9 467.5875
FRS 10 467.6125
FRS 11 467.6375
FRS 12 467.6625
FRS 13 467.6875
FRS 14 467.7125
Channels 1-7 are the same as GMRS channels 9-15. GMRS radios are permitted to use higher power, but an operator can only use the higher power GMRS channels if they hold a GMRS license. (See GMRS below.) In Europe, a similar service to the FRS service is called PMR 446. It should be noted that these frequencies are in the U.S. Amateur Radio service band.
Multi-Use Radio Service (MURS)
MURS is another “licensed by rule” service, which does not require an operator to have a license. The FCC rules for MURS are contained in 47 CFR Part 95 Subpart J. MURS is five VHF channels with 11.25khz spacing or 20khz spacing and 2 watts of power. Range can be up to 10 miles, in ideal conditions. Businesses may use the MURS frequencies, and these are commonly seen as a colored dot on the radio to delineate the frequency. All of the MURS frequencies are simplex only, so a repeater is not permitted. MURS channels are not assigned a channel numbering system, so generally the frequency is used to identify the MURS channel. Most commercial MURS radios use rechargeable battery packs. The MURS frequencies are:
MURS 151.8200
MURS 151.8800
MURS 151.9400
MURS 154.5700
MURS 154.6000
154.470 is also referred to as Blue Dot and 154.600 is Green Dot. These frequencies are also part of a business frequency pool.
Citizens Band (CB)
I would assume that almost everyone has heard of CB radio. If not, go watch Smokey and the Bandit or Convoy. CB radio has 40 channels in the 27Mhz range (11 meter band). Power is 4-watts AM and 12-watts for single side band (SSB). Not all CB radios are capable of SSB transmissions. SSB transmissions cannot be picked up by a scanner. Being in the 11-meter band and close to short wave, radio signals can travel considerable distances, especially overnight. Of all the radio services available to the public, CB is probably the most common, with truckers providing traffic information along the nation’s highways. It is also probably the most abused radio service, with people running illegal amplifiers, jamming, and using profanity. There are a large amount of slang terms used on CB. CB mobile radios require 12v DC, and antennas tend to be long– around 9 feet. Portable CB radios are available, but their range is limited due to the practical length of the antenna needed for good communications. The CB frequencies are:
CB Ch 01 26.96500
CB Ch 02 26.97500
CB Ch 03 26.98500
CB Ch 04 27.00500
CB Ch 05 27.01500
CB Ch 06 27.02500
CB Ch 07 27.03500
CB Ch 08 27.05500
CB Ch 09 27.06500
CB Ch 10 27.07500
CB Ch 11 27.08500
CB Ch 12 27.10500
CB Ch 13 27.11500
CB Ch 14 27.12500
CB Ch 15 27.13500
CB Ch 16 27.15500
CB Ch 17 27.16500
CB Ch 18 27.17500
CB Ch 19 27.18500
CB Ch 20 27.20500
CB Ch 21 27.21500
CB Ch 22 27.22500
CB Ch 23 27.25500
CB Ch 24 27.23500
CB Ch 25 27.24500
CB Ch 26 27.26500
CB Ch 27 27.27500
CB Ch 28 27.28500
CB Ch 29 27.29500
CB Ch 30 27.30500
CB Ch 31 27.31500
CB Ch 32 27.32500
CB Ch 33 27.33500
CB Ch 34 27.34500
CB Ch 35 27.35500
CB Ch 36 27.36500
CB Ch 37 27.37500
CB Ch 38 27.38500
CB Ch 39 27.39500
CB Ch 40 27.40500
Licensed Radio Services
In order to use frequencies in the services below, the user must have a licensed issued by the FCC within that service. A license in one service does not permit use in another service. In some cases, a license applies to all family members, while others apply to the individual only.
General Mobile Radio Service (GMRS)
GMRS is regulated by 47 CFR Part Part 95 Subpart A. GMRS is assigned 15 channels in the UHF band with 8 being assigned in pairs, for repeater use. The other seven are shared with channels 1-7 in the FRS service. A user is required to have a FCC license, usually issued upon completion of an application, and a fee is currently set at $85. The license is valid for five years, and a single license entitles the license holder and immediate family members to use GMRS frequencies. Power on the non-shared frequencies is 50-watts and limited to 5 watts on the frequencies shared with FRS. Repeaters are authorized on the GMRS paired frequencies and can increase the effective range to 20 or more miles, depending on the location of the repeater and antenna. Type approved mobile and portable radios are available for use in the GMRS service. A search of www.radioreference.com or www.mygmrs.com will usually reveal local GMRS repeaters. It is customary to contact the owner and get permission, prior to using a GMRS repeater. When programming a radio, low power should be used on any simplex channel you plan on using for tactical comms.
When accessing a repeater, it will usually be necessary to program a CTCSS tone with the transmit frequency. Sometimes a tone is transmitted by the repeater and can be used to reduce interference on the signal coming into the radio. Most modern radios have the ability to scan the frequency to detect the tone, however, it requires a transmission in order to detect the tone. Some “bubble-pack” radios are now available with both FRS and GMRS frequencies. These use AA or AAA batteries. Unfortunately, the use of FRS and GMRS channels in a single radio, tends to result in the use of the GMRS frequencies by people without a license.
When programming radios with the ability to label the memory channel, a customary naming convention uses “R” for the programming of a repeater pair of frequencies, and “S” is used to indicate simplex. Standard nomenclature is to list the programming for the user radio; therefore, the repeater inputs are the user radios transmit (TX) frequencies. GMRS frequencies are listed below showing the repeater and simplex labeling:
LABEL Rx Tx
GMRS 1 S 462.5500 462.5500
GMRS 1 R 462.5500 467.5500
GMRS 2 S 462.5750 462.5750
GMRS 2 R 462.5750 467.5750
GMRS 3 S 462.6000 462.6000
GMRS 3 R 462.6000 467.6000
GMRS 4 S 462.6250 462.6250
GMRS 4 R 462.6250 467.6250
GMRS 5 S 462.6500 462.6500
GMRS 5 R 462.6500 467.6500
GMRS 6 S 462.6750 462.6750
GMRS 6 R 462.6750 467.6750
GMRS 7 S 462.7000 462.7000
GMRS 7 R 462.7000 467.7000
GMRS 8 S 462.7250 462.7250
GMRS 8 R 462.7250 467.7250
GMRS 9 462.5625 462.5625
GMRS 10 462.5875 462.5875
GMRS 11 462.6125 462.6125
GMRS 12 462.6375 462.6375
GMRS 13 462.6625 462.6625
GMRS 14 462.6875 462.6875
GMRS 15 462.7125 462.7125
Amateur Radio Service
The Amateur Radio Service (aka “Ham” radio) is regulated by 47 CFR Part 97 rules. Individuals must possess a license issued by the FCC. The Amateur Radio Service has more frequencies, in more bands, than any other service available to the general public. There are three “levels” of Ham license, with each one giving progressively more operating privileges in more of the radio spectrum assigned to the Amateur Radio Service. The “entry” level is called Technician; the next is General, and the highest is Amateur Extra, which is commonly referred to as “Extra”. The most common frequencies used by those with a Technician license are in the UHF and VHF bands. Dual band (UHF & VHF) radios type (Part 97) approved are readily available, with some including a third band, such as 6 meters or 1.2 meters (“220” band). Note: Many people are purchasing the Baofeng UV5 series, or similar, radios, which cost as low as $35. While these radios are capable of being programmed to transmit in the VHF & UHF Amateur bands, as well as FRS, GMRS, MURS, and Marine, the radios are only labeled as Part 90 (Public Service) approved. However, having tested one of these radios, they seem to work well on the Amateur bands.
Radios type approved for use in the Amateur Radio Service allow the user to directly enter the frequencies on which the user wishes to operate. Hams can utilize many modes of voice transmission, including AM, FM, SSB, and a digital voice mode called D-STAR (Digital Smart Technologies for Amateur Radio). D-STAR, which utilize UHF & VHF frequencies, as well as the 23 centimeter (1.2GHz), cannot be received by any commercial scanners at this time. (See http://www.dstarinfo.com for more information.) In addition to voice modes, Amateur Radio utilizes many different forms of data transmissions, from morse code to fax and video. There are agreed band plans, designating what frequencies are used for certain transmissions within each band, i.e., only morse code can be operated in some parts of the HF bands, while some frequencies are reserved for digital communications and some for satellite. Hams continue to experiment and utilize a huge variety of communication modes, in addition to “basic” voice communications. Most of these other modes cannot be picked up on a scanner or other conventional equipment, unless you have the same equipment. While voice is best for tactical comms, these other modes provide the users lots of different ways to communicate, including spread spectrum, frequency hopping, and ALE, without being easily intercepted; although you should never assume communications are secure, and the use of encryption or other codes designed to disguise the message are prohibited by the FCC rules. Most portable Ham radios are equipped with NiCad or nickel-metal hydride (NiMH) batteries. Some manufacturers make “clam shell” packs available that are the same size as the NiMH packs but take AA or AAA batteries. It is strongly suggested that you determine if a clam-shell is available for any portable radio you intend to purchase, as rechargeable AA or AAA batteries are going to be easier to use and recharge with a solar panel when SHTF. Mobile radios, including those capable of HF transmissions, operate on 12v DC.
Other Radio Services
Marine Radio
Marine radio operates under 47 CFR Part 80. Recent changes no longer require boats to have a FCC license. Marine radio operates in the VHF band and with an internationally agreed plan of about 80 channels most of which are simplex. FCC rules explicitly prohibit use of a Marine radio while on land. In the U.S., the Coast Guard monitors channel 16 and other channels, and they have considerable direction-finding capabilities to locate ships in distress.
Signals Intelligence (SIGINT)
Signals intelligence is the gathering of intelligence from communications. It includes interception of the communications between individuals or groups (Communications Intelligence) or from analysis of the signal, such as direction finding, to determine who is communicating with whom, the volume (especially changes) of traffic, and the type of traffic. This can be valuable intelligence, even if the actual message is encrypted or coded. It is important to have a basic understanding of SIGINT, so that you can minimize the amount of SIGINT you may give an adversary, as well as enabling you to gather intelligence.
Communications Intelligence (COMINT)
COMINT is the interception and interpretation of the communications message, whether voice or some form of digital message, such as morse code, packet (a Ham radio method), or other digital modes. During World War 2, “code talkers” were used to pass messages in Native American languages that the Japanese could not understand. In addition to their native language, they also used code words to represent something; “tiger” might mean a specific type of boat or weapon. COMINT can also be used to monitor friendly transmission to make sure that information is not accidentally given out that might compromise operations, locations, codes, etc. Some countries, including the U.S., United Kingdom, and Australia used the code word BEADWINDOW followed by a number to indicate the type of inappropriate transmission, if bringing attention to the transmission would not cause further compromise. (Google “BEADWINDOW” for the list of the procedure codes.)
Direction Finding (DF)
Direction finding (“DF’ing”) is the ability to determine the direction that a radio signal is coming from. With a direction from two different locations, triangulation can be used to pin point the location of the transmitter. For this reason, the lowest possible power should be used when communicating, especially on VHF and UHF, or “line-of-sight” frequencies. Using HF signals that bounce off the atmosphere makes DF’ing almost impossible. Other signal methods, such as spread spectrum and frequency hopping make DF’ing impossible; however, the cost of equipment can make availability of equipment difficult. See below for techniques to provide a low probability of detection (LPI).
Low Probability of Intercept (LPI)
LPI is the utilization of techniques to reduce the chance that communications can be intercepted and the use of direction finding to locate the transmitter. These techniques can include:
- Regularly changing frequencies,
- Using split frequencies (This is transmitting on one and receiving on the other, sometimes on different bands; while this doesn’t eliminate DF’ing, it makes intercept of both sides of the communication very difficult, especially when combined with some of the other methods.),
- Making “scheduled” transmissions at irregularly-scheduled intervals,
- Assigning code words for locations, call signs, and specific actions that might be taken and changing regularly (See “code words” below),
- Regularly changing call signs (daily or for each mission),
- Using lowest power possible to pass message,
- Not transmitting from fixed-bases/camps,
- Using directional antennas (which makes it difficult to intercept, unless you are in direct line of the antenna), and
- Keeping transmissions as short as possible.
As noted, use as many of these techniques as possible to reduce the possibility of transmissions being intercepted, understood, or locations being compromised.
Communications Security (COMSEC)
COMSEC is the art of keeping communications from being intercepted in a usable form. This includes physical security of equipment, code books, and encryption keys. Only those with a strict need to know should have access to communications items. This is especially the case with techniques used to code messages, authentication methods, code words, et cetera.
Message Authentication
Message authentication is a process whereby you validate that the sender of the message is who you think they are, or they claim to be. Obviously, this is easier if you recognize the voice of the operator; however, you need a method that could be used by the sender to indicate they are sending under duress. One method is to use a challenge, with a corresponding response. It can be a word that is added at the beginning or end of a transmission. Alternatively, it can be a challenge/response, where the receiver issues a challenge from a list, and the other person has to respond with the corresponding response. No matter what the method, the code word should only be used once. A more subtle authentication uses a phrase that could possibly be part of a normal conversation or message that both parties know is an authentication. There should always be a word or phrase that is used to indicate that the sender is sending under duress but would appear to be an approved authentication.
Encryption
Modern voice encryption uses Advanced Encryption Standard (AES), approved in 2001 and now mandated for use by all Federal agencies. It replaced the Data Encryption Standard (DES) standards that had been used prior to that. Even though AES in the accepted standard, there are many local law enforcement agencies who either don’t use any encryption, or still use the DES standard, due to the costs associated with upgrading. A device called a key loader is needed to generate the encryption keys and to put them into the radios. Radio equipment with DES encryption can be found on a popular bidding site for around $400, with a corresponding key loader for about $400. AES standard radios can be found for between $800 and $1,000, with compatible key loaders around $1,000 to $2,000. Obviously, these costs are outside the budget of most of us. Without knowing the encryption key, it is almost impossible to decrypt the transmission, if AES encryption is being used. If DES encryption is used, it is possible to break it with modern computers. As with other basic COMSEC procedures, regular changing the encryption key reduces the chance that communications can be compromised. However, because of the logistics required to coordinate changing encryption keys in a fleet of radios, poor COMSEC procedures often compromise the encryption.
Code Words
As previously mentioned, code words are used to identify people, units, locations, actions, and a number of other uses. Code words should be changed regularly, such as for each mission, or daily. A master list of words should be created and then the word crossed off when used, so there is no risk that it is used again. A good way to generate words is to search lists for names, planets, ships, et cetera used in TV shows, especially science fiction shows or movies. Using lists like this reduce the possibility of using a word that might be needed in a normal message. Obviously, COMSEC needs to be strictly followed, so ensure that the list of words being used for the specific mission is not compromised.
One-Time Pad Cipher
There are a number of techniques to encode a message without the use of modern equipment, such as a computer or sophisticated encryption programs. A number of these techniques were used during World War 2 with great success. Probably one of the most widely known is a book code; however, these can be broken fairly easily with modern computers. Still, a one-time pad cypher is impossible to break IF IT IS USED CORRECTLY. One-time pad uses a plaintext of random letters or numbers. This is then paired with the text to be sent. The resulting encrypted message, with apparently random letters or numbers, is then sent. The receiver reverses the process to decrypt the message. “Pad” comes from the original use where a small note pad contained the random letters. The page of the pad is used once and then destroyed. So if the top line is the pad of random letters and the line below is the desired message:
AUIQWKDHGUWPKMBVJCUQYTROTNXNDJTHQKOQ
Convey leaves 0600 with commander on board
The sent message is (usually sent in 4 or 5 letter groups):
AUIQW KDHGU WPKMB VJCUQ YTROT NXNDJ THQK OQ
The receiver then reverses to decipher. Both parties then destroy the page with the used cypher.
One potential problem can occur if you have different parties trying to communicate. You have to make sure everyone on the net uses the same page at the same time. One way to prevent this is to have one pad for ”sent” or “outbound” messages and one for “inbound” messages. An additional technique is that the first letter group is the pad page number.
Other versions of a one-time pad cypher use numbers. With a table of characters, numbers, letters, and characters such as space and period, converted to numbers. A similar table of common words is converted to a group of three- or five-digit numbers, with a prefix of 0 added at the beginning to indicate it is a word from the table. In all cases, true randomness is required to generate the pad. Computer programs should be used with caution, as they usually use some pseudo-random calculation. Using numbers has an advantage in that code or commonly used words can be further encrypted by assigning them a number group, i.e., rendezvous can be 2345. Zero can be used as an indicator that the numbers after are a word assignment, i.e., 02345. This give a possible 9999 possible commonly used words and code words. Alpha characters are assigned digits: 1-6 are used for the most common characters, then double digits starting with 7 or 8 and characters, such as . , – + and space are assigned a two-digit character starting with 9. i.e., 99 is a space.
So, if we assigned the following code words a number group as below:
Convoy – 0548
Commander – 0590
Leaves – 0691
0600 – 0858
And the following letter/number assignments (from “The Complete Guide to Secure Communications with the One Time Pad Cypher,” by Dirk Rumenants)
CODE-0 B-70 P-80 FIG-90
A-1 C-71 Q-81 (.)-91
E-2 D-72 R-82 (:)-92
I-3 F-73 S-83 (‘)-93
N-4 G-74 U-84 ( )-94
O-5 H-75 V-85 (+)-95
T-6 J-76 W-86 (-)-96
K-77 X-87 (=)-97
L-78 Y-88 REQ-98
M-79 Z-89 SPC-99
(You should make your own letter-number table, or tables, up for your code. If you make several and assign each a number, you can make the first two digits of your one-time pad # the letter-number conversion table, then the next three digits are the one-time pad number. You have now exponentially increased your encryption complexity. To add additional OPSEC, you should transmit the letter-number table and the one-time pads by different means.)
Then our message:
“Convey leaves 0600 with commander on board” becomes:
69154 (one time pad #) 0(code)0548(convoy) 0(code)0691(leaves) 0(code)0858(0600) 0(code)0590(commander) 5(O) 4(N) 99(space) 70(B) 5(O) 1(A) 82(R) 72(D) 91(.)
So written out in blocks of 5 numbers this becomes:
69154 00548 00691 00858 00590 54997 05182 7291
Note in this example we have assigned a code number for times. If we had not done this, then each digit is sent as: 90(figure) 0000 (the digit is sent 3 times) 90666 90000 90000. This adds 3×5 characters to the message being sent.
If our one time pad #69154 is:
54789 15765 12354 35748 45879 37617 63579 59746 26346 16873 16845
Our encrypted message becomes:
Original Message: 69154 00548 00691 00858 00590 54997 05182 7291
Message Out: 69154 54789 15765 12354 35748 45879 37617 6357
Note the pad number is not encrypted. Otherwise the receiver would not know which pad to use to decrypt the message. For a more detailed explanation of one-time pad cypher, search the Internet for an article “The Complete Guide to Secure Communications with the One Time Pad Cypher,” by Dirk Rumenants.
As with all coded messages, code words, and one time pad cypher’s the “code book” has to be shared with all parties to start with. Ideally, this should be done face to face, because any transmission method to send it presents a COMSEC risk that it could be compromised. You should have a “send” pad and a “receive” pad, so there is no chance of sending using a pad that has already been used. This works especially well when you have multiple groups you need to send messages to.
Transmitting numbers by voice is one way to transmit over the air. However, using digital methods can add another layer of security. Morse code is a very good way to transmit messages, as the equipment is fairly simple. In addition, the number of people who can “read” morse code is relatively small. However, in morse code, numbers are five characters. Another technique is to assign shorter morse characters to each digit, i.e., 0 in morse is —– (5 dashes, or ‘dah’s’); by assigning a . (dit) we have shortened the time to send but also added another level of encryption as in “normal” morse code a ‘dit’ is E. So our morse code for numbers could look something like (brackets indicate normal morse character):
0 -? (T)
1 . (E)
2 . – (A)
3 – . (N)
4 . . (I)
5 – – (M)
6 . – – (W)
7 . . – (U)
8 . – . (R)
9 – -? . (G)
So if we take our message from earlier:
69154 54789 15765 12354 35748 45879 37617 6357
when sent in morse code becomes:
WGEMI MIURG EMUWM EANMI NMUIR IMRUG NUWEU WNMU
Without knowing the one-time pad code, the word code table and the morse code conversation this message would be impossible to understand.
Regardless of the methods used to pass coded messages, the radio operators must follow good COMSEC procedures. The only way a one-time pad cypher can be broken is if the pad is not destroyed after a single use or the original pad is compromised, such as not stored securely or passed to the other operators by a secure method.
As with all skills, you should practice communications skills regularly. Regular participation in scheduled traffic nets done by Amateur Radio operators gives you the skills to copy a message as it is passed and how to pass a message so that others can copy it.
Additional sources of information:
Amateur Redoubt Radio Operators Network