1. Cryptography is a form of code writing with several rules for changing the appearance of messages in order to hide their true meaning. In the old days, this was important, because it allowed kings, for example, to send secret messages to other kings! Currently, encryption is used to send and receive information over the Internet, ensuring that only those sending and receiving the information can see it. In this activity, you will learn to encode and decode your own messages.

2. Of course, to encode or decode a message, you must have a “key”, something that tells us how to do it. The Spy Decoder is the right tool to help us! First, cut out two circles, as shown in the picture.

3. With the help of an adult, make a hole in the middle of each circle.

4. Place the smaller circle on top of the larger one.

Then insert the lace in the centre of the two circles and split open its ends, so that the circles can spin despite being attached to each other.

5. Still don’t know how the Decoder works?
The outer circle represents the letters of the alphabet. The inner circle represents the code that will correspond to each letter.
Line up one of the symbols in the smaller circle with the letter “A” in the larger one. That is, we will choose one of the symbols in the smaller circle to appear underneath the letter A. Let’s line up, for example, the letter A with the circle symbol filled in black, and now each remaining letter corresponds to a different symbol. The “H” corresponds to a “-” line, the “T” corresponds a “^”, and so on.

To write the word “SECRET”, find the symbols that match each letter, then replace each letter with that symbol. The coded word would look like this:

If you align the letter “A” in the larger circle with another symbol in the smaller circle, the word “SECRET” will already be encoded in a different way. Here’s an example:

Only people who know the letters matching each symbol will actually understand your message. If you show an adult these symbols, they won’t know what they mean unless you tell them.

6. The Decoder you have created also allows you to decipher messages from other people!
Please note that if you want to write and receive secret messages from your friends and know how to decode them, your Decoders must be the same, and must be aligned in the same way. In other words, each letter must match the same symbol.
For example, if the letter ‘A’ corresponds to the black circle on your Decoder, but on your friend’s Decoder it corresponds to the star symbol, you will not be able to understand the message.
To be able to talk in code, if the letter ‘A’ corresponds to the black circle on your decoder, it must also correspond to the black circle on your friend’s decoder, and so on for the other letters. Once your Decoders are aligned in the same way, all you have to do is receive the coded message from your friend, look for the symbols and replace them with the letters! Line up the Decoder, as shown in the picture, and decipher the word:

If you found the word “COOKIE”, congratulations! You have successfully deciphered the secret message!

7. Have fun writing secret messages with your friends!

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