I think that once we were all students we sent secret messages in class or notices to classmates to let them know that secret message. But we have always had the uncertainty that this message or that note would fall into other hands ... they would discover our secret !!!

Without realizing it, we were looking for or imagining how to encrypt that message, that is, we were getting a bit closer to cryptography. Well, what better way than it is, to be able to explain to our students a little math doing a cryptography activity.

To do this classroom activity I have proposed it as a gamification, what better than to create an adventure of spies in the Second World War, in which the encryption and deciphering of codes became another front of the struggle.

First of all we are going to explain that it is cryptography; word that comes from krypto (hidden) and graphos (writing), is the discipline that is responsible for the encryption and decryption of messages, ie masking messages through an algorithm that must also allow return the message to its original state.

Cryptography, historically, has been linked to military campaigns and the secrets of governments, in fact, it is said that the first cryptographic technique was used in the fifth century BC in ancient Greece and even, later, by Julius Caesar in his military campaigns

We must know that all encryption consists of two parts:

**Encrypted message****Secret password**

What is the secret key for?

The secret key to encrypt and decrypt the message, therefore if our encrypted message falls into "enemy" hands, if it does not have the secret key it will be very difficult to decipher it.

Once we have more or less clear that it is cryptography and the possible mathematics behind it, we have to download it to be able to take it to a class activity with 6º Primary students.

For this we will focus on two encryption methods, simple and easy to use by our students.

One of them is the **CESAR method** Or encryption of displacement, and **what does it consist of?**

For it consists in moving the letter that we want to encrypt as many places to the right of our alphabet as the secret code indicates.

**For example.**

Julio César proposed the previous cryptosystem for the key k = 3. In this way, we substitute each letter of the message for which it is three positions further in the alphabet, as shown in the table. From the last letter, the "Z", we will start with the "A"

If we want to encrypt the word ** HELLO** in 3 code, the result will be

**hi ==>**** krñd**

We can even make complete sentences, such as:

** ****A sunny day ==>**** zr inf xtpjfit (Key 5)**

**The red car ==>**** ms kwkom zwqw (Key 8)**

** **The second method that we are going to explain and that we can take to our classroom, is the method of the scythe.

What is a scythe?

The Scythian (Greek:*skytálē*) is formed by a round cane on which was wound a long and narrow parchment ribbon in which a message was written (once the ribbon was wound on the stick) so that, when unwinding the ribbon, the letters appeared in different order and meaningless. To decipher the message, it was necessary for the receiver to have a stick of the same diameter, so that he could read the original text by rolling it over the stick.

In this type of cipher the text is not modified, but the order in which the symbols of the alphabet appear is mixed.

This type of cryptography can be worked in the classroom as a plastic work creating with our students our own scythe and encrypt messages. I leave a video where he explains how to make one, https://www.youtube.com/watch?v=RwCBAnxg2DI

But to continue with our digital activity, we are going to turn this scythe into something that we can do in a mathematical way. For that we use as secret key, the rows.

An example to understand it

We encrypt the text «**I like ice cream**»With the secret key 4

The encrypted text would read: «**MSLAETHDGAEOUEL** » To explain its operation, we will do it with the decryption transformation, in which the secret key should be known, which in this case is 4, that is, 4 rows.

Therefore we separated into groups of four starting from the beginning.

**MSLA EthD GAEO UEL**

We place in our table (escítala) in 4 rows

M |
E |
G |
U |

S |
T |
A |
E |

L |
H |
E |
L |

A |
D |
O |

If now we read it following the rows, we get "**I like ice cream**" We already have our message!

An adventure of spies in the Second World War

Once we have explained the concepts in the classroom, we can do this in a session, by means of small exercises to encrypt some messages among our students, especially so that they can get the idea.

Now that we have everything ready, we prepare the next session, the gamification by means of a classroom activity.

I have prepared the game board with Deck.toys where we prepared a spy story based on World War II. The objective of our mission is to recover the Enigma machine that is in London, passing through different cities where we will have to solve encrypted messages and mathematical exercises ... **THRILLING!!!**

The working method can be done in groups of 3 or 4 students with a device (computer or tablet). The exercise is totally autonomous, therefore each group will work at their own pace and the activity will end when one of the teams shows us the photo of the famous «Enigma machine» hidden in London.

Little by little they will be guided by the "allies" to pass through the different cities, where before entering or receiving the following message they will have to pass a test, such as solving square roots ...

Choose your corresponding result

Or for example to know what alphabet the Germans use and decipher a message to enter Belgium.

But since I do not want to give you more clues about this adventure, I'll leave you **«The path of the Enigma»** so you can play freely and use it in your classroom.

### deck.toys/mathsprimary

Any doubt or improvement that comes to mind do not hesitate to tell me to continue improving the adventure. If you need help on the management of this fantastic tool called Deck.toys, I am preparing a manual to upload it and help you.

In search of enigma !!!