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Class 3
Chapter 1: What's in a Name?
A cipher is a way to scramble a message so only someone with the right key can read it. The Caesar cipher shifts every letter forward by a fixed number of places.
Learning outcomes
- Encode and decode short messages with a Caesar cipher
- Recognise that a 'key' is needed to read an encrypted message
- Reason about why information needs to be kept private
Activities
- Caesar-cipher encoding game with shift keys
- Find hidden number-names inside letter grids
Worked examples
Read through these first, then try the practice below.
Example 1 — Encoding with shift = 1
Encode the word CAT with a shift of 1.
Solution: Shift each letter one place forward: C → D, A → B, T → U. The encoded word is DBU.
Example 2 — Decoding with shift = 3
Decode the word EBP using shift 3.
Solution: Shift each letter three places backward: E → B, B → Y, P → M. The decoded word is BYM (which is not a real word — try other shifts when decoding!).
Self-do practice
Question 1 of 3 · Score 0/0Encoding A with a shift of 2 gives which letter?
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