I believe that channel 3 carried the timer signal, while channel one was for voice - usually used for maintenance and some times clear reading of one time 5 day pad code, while the 4th channel was high level encrypted data and voice.
All of that on a single carrier wave - which was complex to break out, however some guy who was a ham in civi life hand-wound copper coils which split the channels into discrete recordable signals.
With the Internet, there are other ways to hide data - like in images. But, that is found in military-like orgs not civi business and personal transactions.
Some guys like to prattle on about this or that distro, but that is all it amounts to - prattle. Each civi scheme is either already broken prior to public release or has built-in backdoors.
Only big mils have the will and money to make and brake secure crypto which only lasts for a while before come other mil breaks it. NSA does not spend major efforts and money on low priority crypto schemes. All traffic is graded according to particular classes - with business ranked just lower than mil air, with civi personal at the bottom.