The security of communications is dependant upon who you want to protect it from and how much money you want to spend doing so.
Non-encrypted radio communications are vulnerable to handheld or larger scanners. Privacy codes can be easily overcame by hand held scanners. Inversion of verbal communications - same thing,...easily decrypted with a plug in SD card.
Verbal communications can be protected to a degree through the use of brevity codes. This is nothing more that anticipating what you need to verbalize on the radio and condensing that to a pre-planned brevity.
An example of a brevity code would be an element from your survival site is conducting a security patrol around the survival site. Maybe you use a brevity code like this: ALPHA = Situation normal, conducting patrol; BRAVO = in Sector One; CHARLIE = in Sector Two; DELTA = in Sector Three; ECHO = conducting short term halt; FOXTROT = have eyes on armed group; GOLF = <10; HOTEL = <20; INDIA = >20; JULIET = moving back to camp; KILO = 15 minutes from re-entering Survival Site. So with this brevity code, if the patrol sends a "DELTA, FOXROT, GOLF" it means they are in patrol sector three and are observing an armed group of less than 10 people. This keeps transmission times down and protects the information you are sending over the air.
So the bottom line on brevities is that a one or two word phrase has an elaborative meaning to condense transmission times. However, continued use of the same brevities would allow a intercepting station to piece together your code.
Another, much more secure method, abeit time consuming method of encrypting messages is through letter transpositions using a tri-graph. See the diagram below:
You need a key to encrypt your message against. A book is a good example, and in some circles this is called a “book code”. Let’s say you and your survival partners decide on a book, and a method of ensuring the other party knows which page to use to decrypt. At the beginning of each message you can say or write “ONE THREE HOTEL FIVE XRAY”. The end user knows to remove the letters to get 135 and that would be the page to start on.
You are part of a survival group that is Bugging Out tomorrow night to a Bug Out Location and you want to let the people in your group at the BOL to know to expect you. You want to send the message “WE ARE MOVING TOMORROW NIGHT, TUES NIGHT, TO YOUR LOCATION”. You add “ONE THREE HOTEL FIVE XRAY” to the message to tell the other group that this is the page they should be encrypting from.
From page 135 of the book, you writes the text from the book in groups of five letters. In this case “Out in the meadow was a blue van with all four tires flat and all windows busted,….” In groups of five letters and underneath those letters you write the message “We are moving tomorrow night xx Tues night xx to your location” (note 1: use double x to indicate a commo or repeat - or to fill up spaces; use triple x to indicate a break or period). (note 2: writing out the book code in groups of five letters just makes it easier to encrypt with tri-graph).
(from book)
OUTIN THEME ADOWW ASABL UEVAN WITHA LLFOU RTIRE SFLAT ANDAL LWIND
(message to be encrypted and sent)
WEARE MOVIN GTOMM ORROW NIGHT XXTUE SNIGH TXXTO YOURL LOCAT IONXX
From here you use the Tri-Graph to transpose the letters. From the Tri-Graph find the “O” on the top line then the “W” in the left column then see what letter intersects,.... it should be the “K”. From the “U” and the “E” you should get a “Y”, and so on.
Your final encrypted message would be: KYTZR FVZUR GQCII OJRPH HMBHG TFMBE DYNUB KQFKS QTFRE LBFAE TKVKA
You would send that via e-mail, text or voice communications,....if by voice then you would phonetically sound out each letter,… “KILO YANKEE, TANGO, ZULU, ROMEO, etc.
At the other end your encrypted message would be written underneath the same phrase, it would look like this:
(from book)
OUTIN THEME ADOWW ASABL UEVAN WITHA LLFOU RTIRE SFLAT ANDAL LWIND
(message to be de-crypted)
KYTZR FVZUR GQCII OJRPH HMBHG TFMBE DYNUB KQFKS QTFRE LBFAE TKVKA
It would be decrypted at the other end by locating the “O” on the Tri-Graph, going horizontally across to the “K” then looking across the top of the Tri-Graph to see what letter than pertained to, and in this case a “W”. The same for the next letter, which is a “U”. Locate the “U” on the left hand column of the Tri-Graph, go across to the “Y” then up to the top of the Tri-Graph and you should get a “E”, and so forth.
Messages using this manual encryption could be written on paper and passed either face to face or through a dead drop if you are in a situation where a threat has the ability to intercept and direction find your phones or radios, and the telephones are either down or monitored. If a occupation force or a nearby threat has intercept and DF capability, then talking in an obvious code would spin them up and draw attention to you.
