Write your key word, dropping any repeated letters, then finish the alphabet with all the letters you have not used yet. That gives you a mixed-up cipher alphabet you can rebuild from memory, so there is no key to lose or steal.
The beetle that taught a nation to crack codes
Edgar Allan Poe put a scrambled alphabet at the center of his story The Gold Bug, and had his hero break it by counting how often each symbol appeared. The story was a sensation and taught a generation how code-breaking works. Fifty years later Arthur Conan Doyle borrowed the trick for The Adventure of the Dancing Men, where the symbols are little stick figures waving flags.
Print this page and you get a worksheet: how the cipher works, where it came from, and the puzzles to crack, with the machine and the menus left off.
Print this page as a worksheet Its sheet in the pack Try the challengesLonger, harder and written for grown-ups. Worth a look when this page runs out.