Challenge type: Secret Codes · Difficulty: ★★★☆☆ Medium · Code: Mirror code
Beep found this note under the keyboard. The letters look all mixed up, but there’s a trick!
The secret message
ZHGILMZFG
How the code works
This is a mirror code (its real name is Atbash). The alphabet is flipped: A swaps with Z, B swaps with Y, C swaps with X, and so on. Use the two strips in the picture to swap each letter back.
Fun fact: the mirror code decodes itself. Encoding a message twice gives you the message back!
Need a hint?
The first word of the answer has 9 letters and starts with A.
For teachers and grown-ups
Skills practised: Algorithms, encoding and decoding, and logical reasoning (cryptography basics).
The big idea: A cipher is an algorithm. Knowing the method and the key lets you undo it.
Questions to ask:
- What does the key (the shift) do?
- How could you crack a shift code without knowing the key?
- Why are simple codes like this not safe for real secrets?
Take it further: Make the paper code wheel from our printables and send messages between groups.