Those kinds of puzzles? Hmm, it looks like you got some response at !encryption and I’m glad to see some activity there, but in general it’s intended to be more about modern, computer-based cryptography. You might like to read “The Code Book” by Simon Singh which is a general introduction to the subject, starting with old fashioned hand ciphers like the one you posted, and moving up through the modern stuff. “The Codebreakers” by David Kahn is a wonderful history-of-cryptography book, mostly about the pre-WW2 era. And the greatest crypto story ever told is the WW2 Enigma attack, which probably shortened the war by years. “Battle of Wits” by Stephen Budiansky is a good book about that. Kahn’s book came out in the 1960s when the Enigma story was still classified. There was a later edition where a brief mention was added, but it didn’t say much.