Securing your telephone calls

At the time of the Cold War, if you wanted to have an extremely secure communication over an insecure communications channel, the only choice was to have somehow arranged an earlier secure communication over a secure channel.  The iconic image of a diplomatic courier handcuffed to a briefcase was no mere icon.  For many years at the height of the Cold War, the State Department distributed special phonograph disks to US embassies around the world containing the audio equivalent of the “one-time pads” that were used for secure encryption of character-based messages.  The briefcase containing the phonograph disk counted as the “earlier secure communication over a secure channel” that permitted a later secure communication over an insecure channel such as an international telephone call or a radio communication.  You can read about this program, called SIGSALY, in this Wikipedia article.  By now in 2019 you can have telephone calls that are nearly as secure as the SIGSALY communications, and there is no need for any “earlier secure communication over a secure channel”. And the equipment that you will use is inexpensive when compared with the prodigiously expensive SIGSALY equipment.

The first breakthough for the kind of secure communications that I am talking about was the Diffie-Hellman (“DH”) algorithm.  Using this extremely clever procedure, two parties can pass messages back and forth over a nonsecure communications channel and can arrive at a shared key that can then be employed to conduct secure communications over the nonsecure communications channel.  It means that to have a secure communication, there is no longer any need to have had some previous secure communication.

DH was published and patented in 1997 and the patent has by now expired.  The technique continues to be used to this day, securing all kinds of communications including web pages, credit card transactions, and telephone calls.

It has for some years been easy and inexpensive to use very high quality encryption (including use of DH) in the connections between your telephone PBX and your telephones.  In recent times it has begun to be easy and inexpensive as well to use such high quality encryption in the connections between your PBX and your telephone service provider.  I give an example of the latter in this blog article.

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