One-time pads are uncrackable ciphers. Read about them here, then follow our instructions to make your own.
You will need:
A Pack of cards
Two empty notebooks
Shuffle a pack of cards well.
Turn over the top card.
Lookup the number for the card in the table and write it in the next space in the notebook.
Put the card back in the pack and shuffle.
Repeat from step 3 until you have enough numbers for your message.
Copy the numbers exactly in to the second notebook.
Each number tells you the number of places to move on in the alphabet, wrapping round from Z back to A for the next letter you want to encrypt. Cross the number out once used and never use it again. That is why it is called a one-time pad!
The person who gets the message must use their copy of the one-time pad, moving back in the alphabet the given number.