If you would like a classic primer on the subject I would highly recommend Alexander D’Agapeyeff’s famous 1939 work,
“Codes and Ciphers - A History of Cryptography”The term you were looking for is a polyaphabetic cypher. The best known is the Vigenère cipher.
These were state of the art through WW1. Today they can be solved in less time than it takes to set up the decode on the computer. I have done one using pencil and paper.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
If you would like a classic primer on the subject I would highly recommend Alexander D’Agapeyeff’s famous 1939 work, “Codes and Ciphers - A History of Cryptography”
The term you were looking for is a polyaphabetic cypher. The best known is the Vigenère cipher.
[alphabet grid and live links are shown in Lone Palm’s post]
These were state of the art through WW1. Today they can be solved in less time than it takes to set up the decode on the computer. I have done one using pencil and paper.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
~ ~ ~ ~ ~ ~
Thanks for the links and pointing the direction to where to learn more about Codes and Cyphers. I had always intended to do more with Cryptology, but have been distracted over the years with pursuing other stuff.
I knew those examples I used were sub-elementary, but for me they were useful to at least grasp some concepts in a dim way of what the Big Boys might be up to, and to at least grasp the possible relevance to POTUS’s tweets of what I was seeing when I pulled up the acronym.
Thank you again for the MOST helpful info, Lone Palm!