Create Your Own Secret Code
This is a substitution code: swap every letter of the alphabet for a different one, agree the swap with a friend ahead of time, and you can both write messages nobody else can read.
- Paper
- A pencil or pen
Build your code
- Write out the whole alphabet on a piece of paper.
- Underneath it, write a new letter for each one. For example A becomes D, B becomes E, C becomes F, and so on.
- That second row is your code alphabet. Keep it safe — it is the key.
- Write your message using the code alphabet instead of the normal one.
- Give your friend a copy of the code alphabet, and the message.
- Your friend reads the code alphabet backwards to turn the message back into ordinary letters.
An example code
Here is a simple one, where every letter shifts along by three:
Original: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Code: D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
To write "HELLO" with this code, look up each letter in the top row and write down the one underneath it. H becomes K, E becomes H, L becomes O, L becomes O, O becomes R. "HELLO" comes out as KHOOR.
Reading a message
To decode, you do the same thing the other way round: find each letter in the bottom row and write the one above it.
Let's decode KHOOR:
- K is above H
- H is above E
- O is above L
- O is above L
- R is above O
So KHOOR is HELLO again.
Try this next
- Make a harder code — shift by seven instead of three, or scramble the whole alphabet.
- Use numbers or symbols instead of letters.
- Leave a coded note somewhere for someone in your family to find.
Keep your key somewhere safe — a code is only secret while the key is.