Polybius square

Polybius square is like a big playground where letters and numbers have their own special spots to play. It's like a giant game board where every letter and number has its own little space to live in.

Imagine you have a square with numbers 1 to 5 on the top and letters A to E on the side. In each little square, you put a combination of a letter and a number. For example, A1, B2, C3, and so on.

Now, when you want to send a secret message, you replace each letter with their corresponding number and write them down underneath each other. For example, if you wanted to send the message "HELLO", you write down the numbers 2, 5, 3, 3, and 4.

Then, to encrypt the message, you use the square to find the corresponding letter for each number. So the numbers 2, 5, 3, 3, and 4 would give you the letters BCACC.

So when someone gets your secret message, they have to use the same square to translate the letters back into numbers, and then the numbers back into letters, to read your message.