GeoGebra Classroom

# Cryptography and Coordinates

Your school prohibits using cellphones during school hours, but you and your friends found a way to communicate using encrypted messages, so that just those who have the key can understand the content of the message. Here is your key! It's a grid, containing all the letters of the alphabet. Each letter has its own coordinates, and only who has the same exact grid can decode the message.

## The Signature

Every message must be signed, in order to understand who is the sender. My signature is . What is yours?

## Separating Words

An encrypted message must be understandable though! We will separate words by enclosing each one of them in braces. Write an encrypted message to a classmate.

## Securing Data

Securing data is the core principle on which cryptography methods are based. If we used as key just the x-coordinates of the points that you see in the grid, would this method be as safe as the original one? And what if we used only y-coordinates? If you had to choose between x-coordinates or y-coordinates only to encrypt your message, which of the two methods would be the most efficient and safe? Explain your choice in detail.

## Create Your Own Decryption Grid

Drag the points in the app below to create your own decryption grid. Points must respect the following conditions: - each point must have unique coordinates - the x-coordinate of the vowels is -1 - the x-coordinate of D is -6 - the x-coordinate of H and K is -5 - points W, X, Y and Z belong to the y-axis - points L, M, N, R, S and T belong to the x-axis - the y-coordinate of B, F, J, P and V is 3 - points C, G, and Q have their x-coordinate equal to their y-coordinate