Write the message into a grid. Above the grid write a key word, and number its letters in alphabet order. Now copy out the columns in the order those numbers give you. Change the key word each week and you have a brand new cipher.
The cipher you can carry in your head
Column ciphers travelled well because they need nothing but a pencil, a scrap of paper and a word you can remember. No machine to capture, no key sheet to be found in your pocket. Armies could change the key word every day just by passing on a single word, and a soldier who was searched was carrying no evidence at all.
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.