My holiday reading this year was The Code Book by Simon Singh . I highly recommend it to teachers of Mathematics and Digital Technologies as it brings amazing insight into the world of codes and cyphers. Tracing 2000 years of code makers and code breakers, the secret world of cryptography is unveiled. In a modern technological age where each and everyone of us send messages and information through a digital platform, we are both protected and vulnerable to the cryptographer. The ability to unlock the key of complex modern day cyphers, potentially gives the people with this knowledge unlimited power over others.

### Prime numbers and factors are what is keeping your digital information safe

I have two year 7 classes this year, and as I worked with them on factors and prime numbers this week, cryptography helped bring understanding to them of the importance of number theory in a technology driven world. Prime numbers and factors play an important role in the first public key security cypher RSA . The public security key is a combination of two very large prime numbers being multiplied together. The security of this cypher lays in the fact that to find factors of numbers it quite a complex task. Using current technology the computer algorithm used would take forever to find these two prime factors.

Just as the Turing Machine (the first computer) was a game changer in WW2 to crack the Enigma Code. The invention of a quantum computer could potentially be able to find the prime factors of the security keys and the digital security we currently take for granted would change. 2018 Australian of the Year, Professor Michelle Yvonne Simmons was recognised for her research in the field of Quantum Physics, in particular her work on quantum computers.

### For cryptographers the invention of a quantum computer would be this century’s game changer!!

So next term when the year 7 students are studying Ancient Rome in HASS, I will use this opportunity to teach them about the Caesar Code. Dominating the first Millennium this cypher was considered unbreakable until the Arab Cryptanalysts, the code breakers, combined linguistics and statistics to decipher hidden messages using the frequency analysis of letters.

So how does the Caesar Cypher work? It is called a simple mono-alphabetic substitution cypher. You decide on a number between 1 and 26 and you simply move the letters of the alphabet this many places. This number chosen is called the key as it enables the person who has the key to unlock the hidden message. For example if the chosen key is 4, then each letter of the alphabet moves four places, so a becomes e and b becomes f etc.

**The Caesar Code is perfect for use by young adolescents who may want to send secret messages to their friends**

This code, even though unbroken for 500 years is now quite simple to decipher. The frequency of the letters gives us a clue to what each letter represents. So our young codebreakers would need to create a frequency distribution table and then comparing the distribution to the one below they could discover the key.

A slightly more complex take on this is to use the Vigenere Cypher. Instead of a number key, a word is chosen as the key, for example,** cake**. Each of the letters in the message then move the position number of the letters of the word. i.e letter one moves 3 places, letter two moves 1 place, letter three moves 11 places and letter four moves 5 places.

#### ‘deciphering is, in my opinion, one of the most fascinating arts” – Charles Babbage

As communication techniques have improved over history, telegram, radio, telephone and now computers, so has the level of security required to keep information safe. No longer just the realm of military, government institutions and large business the encryption of private information is important to us all. While not every student will go off to study cryptography at university, I like to think that this introduction gives them some basic understanding of the importance of security of data.