Every letter moves along
The Caesar cipher shifts the alphabet by a fixed number. With shift 3, A becomes D, B becomes E – and Z becomes C, because the alphabet starts again. Julius Caesar is said to have protected his military mail this way. The shift is the key; whoever knows it turns everything back.
The cipher wheel to cut out
Instead of a table, this page prints a cipher wheel: two circles with the alphabet, the small one on top of the large one. A paper fastener goes through the middle, and the inner disc turns. Outside is the plain text, inside the cipher text. The printout already shows the wheel in the chosen position – for a different shift, simply keep turning.
- Cut out both circles along the dashed line.
- Place the small disc centred on the large one.
- Push a paper fastener through the cross in the middle and bend it over at the back.
- Turn the inner disc until the key letter inside sits under the A outside.
Shift 1 to 25
The slider sets the shift; the preview immediately shows the new cipher text. Umlauts become AE, OE, UE and SS first so the 26-letter alphabet is enough. If you would rather print a table than the wheel, untick “cipher wheel”.
Why Caesar can be cracked
There are only 25 possible shifts. A patient child tries them all – which is exactly what the decoder does with the slider in seconds. A good moment to explain why real encryption needs much longer keys today.