by Holly Webb
Code or Cipher?
Most people don’t know this, but codes and ciphers aren’t the same. A code is a way of taking a message and making it much shorter and simpler. It works by thinking about what the words or letters mean – so you might send “What time is it?” in code by sending a clock emoji. The thing to remember is that for a code you need a codebook – like a dictionary that tells you what each codeword or picture means.
A cipher doesn’t care what the message means at all! It’s working just by symbols. A cipher uses an algorithm, which is like a set of secret instructions that tell you how to change the symbols in your message. It sounds complicated, but it really isn’t…
Substitution Ciphers
This kind of cipher works by keeping the letters in your original message (which is called the plaintext) in the same order, but replacing them with the coded message (which is called the ciphertext) by using an algorithm that turns the letters into different ones. Substitution is just another word for swapping one thing with something else.
Caesar Cipher
The most famous substitution cipher is supposed to have been invented by Julius Caesar! The Caesar cipher was used to send messages to his armies. He would write out his message and then change every letter to the letter that came three further on in the alphabet. So A would be D, and B would be E. The algorithm for this cipher is just “Add three”.
So Penhallow Hall would be: SHQKDOORZKDOO! But to make it harder to solve, you can put some extra spaces in to make the words look different: SHQKD OO RZKD OO.
You might think that this was a bit of an easy code for a military leader who was sending out secret orders, but many people in Julius Caesar’s time couldn’t read at all, so this code would have seemed even more confusing. Enemies intercepting a coded message might have thought it was in a completely different language.
Transposition Ciphers
Transposition ciphers work a bit differently. This time you’re keeping the same letters, but moving them around following the secret instructions in your algorithm. Transposition is a word that means moving something from one place to another.
Reverse Order Cipher
One really easy transposition cipher is the reverse order cipher. You write your message backwards. So Penhallow Hall would be: LLAH WOLLAHNEP. Or you can work the cipher slightly differently and keep the words in the same order, and just reverse the letters: WOLLAHNEP LLAH.
Book Code
Nat and Jake send their secret messages with a book code – even though their book is actually a ballad sheet.
This is a code rather than a cipher, because you’re looking for specific words.
This is a really good method, as long as all the words you need are in the book! The important thing to remember is that you must both have exactly the same book. Even if you both have a copy of Matilda by Roald Dahl, they may have been printed at different times so all the words will be in different places, and your messages won’t make sense.
To send a message, you find the word you want and write down the page it’s on, then the number of the line (from the top of the page counting down) and the order the word comes on the line (from left to right).
Can you solve this message? You’ll have to guess which book I’ve used first…
Hold the last page of this book up to a mirror to check your answer!
Copyright
STRIPES PUBLISHING
An imprint of The Little Tiger Group
1 Coda Studios, 189 Munster Road,
London SW6 6AW
First published as an ebook by Stripes Publishing in 2018.
Text copyright © Holly Webb, 2018
Illustrations copyright © Jason Cockcroft, 2018
Author photograph copyright © Nigel Bird
eISBN: 978–1–84715–988–5
The right of Holly Webb and Jason Cockcroft to be identified as the author and illustrator of this work respectively has been asserted by them in accordance with the Copyright, Designs and Patents Act, 1988.
All rights reserved.
Apart from any use permitted under UK copyright law, this publication may only be reproduced, stored, or transmitted, in any forms, or by any means, with prior permission in writing of the publishers or, in the case of reprographic production, in accordance with the terms of licences issued by the Copyright Licensing Agency.
A CIP catalogue record for this book is available from the British Library.
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