Creating security codes for transmitting information via radio requires close knowledge of regulations governing the use of radio and tools such as the International Radio Operators Phonetic Alphabet and Morse code. Many radio security codes are substitution ciphers.
Radio transmissions are secured using codes based on industry regulations and standards such as the International Radio Operators Phonetic Alphabet that starts with Alpha, Bravo, Charlie, Delta and Echo to spell words. In certain situations, operators may have to use Morse code to secure a transmission. In addition, groups of operators compose lists of code words with an agreement on what they means. For instance, “House Tango” can signal that an operator is getting into a car. Because radio transmissions can be heard by people outside the radio group, good code words don’t call undue attention to themselves. They also don’t reveal identities or locations of operators.
Before radio operators can begin secure transmissions, they must have a secure way to identify themselves on air. This is done using an authentication table, a matrix of signs and countersigns. To construct one, first make a table with nine columns, and number each 1 through 9. Then add rows as necessary, and letter them starting with A. Then fill in the blank cells with random values. When one operator transmits a sign such as Alpha Two, for instance, only the correct recipient should know the correct countersign.