From The RadioReference Wiki
KY-65 is a voice encryption mechanism designed to work with HF Radio communications.
KY-65 uses the Parkhill encryption protocol, which works by dividing the 300 to 3,000 Hz voice frequency range into 9 sub bands, each 300 Hz wide. The signal in any of these 9 ranges can encrypted and/or inverted. This results in 18 points that can be changed 9 times or 18!/(18-9)! = 17.6 billion "keys". Note that the key is a fixed permutation of the sub bands and does not change with time like the more modern voice encryption systems, so no date - time input is needed.
Users of KY-65
- COTHEN Network