Concept 2 of 6
Letter Codes: Shift the Alphabet
Today's big idea
Find the shift between one letter pair, then apply it to the rest.
A shift moves every letter the same number of steps, wrapping Z round to A.
How it works
👀 What's going on?
Spies and secret clubs hide messages by nudging every letter one or two steps along the alphabet. The reader who knows how far you nudged can undo it in seconds. Everyone else just sees nonsense.
💡 Here's the trick
The code above turns CAT into DBU. Every arrow says the same thing: +1. That sameness is the whole secret. Find the shift once, from any single pair, and it works on every other letter.
🪄 How to do it
- 1.Pick one letter pair from the code above and count the gap between them.
- 2.That gap is the shift, and it is the same for every letter.
- 3.Move forward by the shift to code, or backward by the shift to decode.
✍️ Try it
BUN is coded as CVO. What is the shift? Now the harder one: using that same shift, what is the code for MAP?
B to C is one step, and so are U to V and N to O. The shift is +1. Coding MAP with +1 gives N, then B, then Q, which spells NBQ.
⚠️ Watch out
You might be thinking a shift can push a letter off the end of the alphabet. It cannot. There is nothing after Z, so the count loops straight back to A. Shift Y by 2 and you land on Z, then A, so Y becomes A.
🌟 Why this matters
A shifted note is the simplest real code there is, and children have used it to pass secrets for hundreds of years. The apps on a phone scramble messages the same way, only with far bigger jumps than one or two steps.
Exam tip: Always check two letter pairs before you trust a shift, because one pair can be a lucky guess.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“If CAT is coded as DBU, what is HAT?”
- 1
Find the shift
C → D is +1. A → B is +1. T → U is +1. Shift = +1.
- 2
Apply the shift to each letter of HAT
H + 1 = I. A + 1 = B. T + 1 = U.
- 3
Glue the letters together
I + B + U = IBU
- 4
Answer ✓
HAT → IBU
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Shift +1 means count 1 letter forward in the alphabet for each letter.
CIPHER · ROUND 1 OF 3
Shift rule: each letter moves +1 forward
Example: A → B, B → C, C → D
Original Word
Code the next letter: C + 1 = ?
Quick check
✅ VERIFICATION
A code shifts every letter forward by 2, and the code word is OWF. What is the real word?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Symbol Equations
Find one shape, then substitute it everywhere.