Write the alphabet forwards, then write it again underneath backwards. Every letter swaps for the one below it. There is no key and nothing to remember: A pairs with Z, B with Y, and so on to the middle.
Because the pairing works both ways, encoding and decoding are the same job. That is also its weakness: anyone who has seen it once can read it forever.
A cipher hidden inside a holy book
Hebrew scribes swapped the first letter of the alphabet for the last, the second for the second last, and so on. It appears in the book of Jeremiah, where the word Sheshach stands for Babel — Babylon. Nobody knows whether it was meant as a secret, a scribal game, or a way of naming a dangerous place without writing it down. It is the oldest cipher on this site, and the only one with no key 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.