# Encryption

## Starter

Write as many single words that come to mind when you hear the word “encryption”.

## Learning Intentions

• Understand and be able to explain the terms ‘encryption’ and ‘decryption’

• Understand the purpose, advantages and disadvantages of encryption

## Success Criteria

• I can explain the term encryption
• I can explain the need for encryption

## What is encryption?

“the process of converting information or data into a code, especially to prevent unauthorized access.”

## What is encryption?

“the process of converting information or data into a code, especially to prevent unauthorized access.”

## Converting from one value to another

• Conversion is an important part of computer science.

• Any computer program is written in text and converted (properly known as compiled) into something else.

## Converting from one value to another

• Encryption involves conversion where an input value goes in and is processed into an output value.
• Encryption involves transforming a human readable piece of data into something that is unreadable.
• For example using an encryption method:

testword => ty/c3NIfUnz6jrZAU9jDeg==

## Alphabet cipher

• Alphabetic ciphers are so simple that they barely protect a message at all.
• All you do is replace each letter with a number.

London Bridge

becomes

1215140415014 021809040705

Note that two numbers have been used for all letters, for example B would be 02 not 2.

## Caesar Cipher

• In around 50 BC, the Roman dictator Julius Caesar developed his own encryption method for communication with his front line commanders.
• This became known as the Caesar Cipher and was one of the earliest types of encryption.
• Although it is relatively simple, it was incredibly successful for Caesar.

## Caesar Cipher

• It works by shifting each character in the alphabet along. Caesar used a shift of three so A became D and B became E and F became I.
• By shifting the characters back the way the message could be decrypted and read.
• Spaces remain the same!
• If we shift each character in the alphabet along 4 we get:

A B C D
E F G H

## Caesar Cipher

Complete the Caesar cipher part of the worksheet using a shift of four.

## Caesar Cipher

• Now encrypt the following using a shift of 7:
1. Today it is going to rain

2. Meet me under the clock tower

3. Go to Paris

avkhf pa pz nvpun av yhpu

tlla tl bukly aol jsvjr avdly

nv av whypz

## Book cipher

• Book ciphers require a copy of a book that both parties have access to.

• To encrypt, you simply look for words you want in your message, then write the page number and the word number on the page.

• The book that is used to decrypt must be the exact same edition as the book used to encrypt as in most cases other editions will have slight alterations to them that could change the message.

• Decrypting these can be quite slow but it's a very secure algorithm.

## Spelling (mistake) cipher

• Spelling ciphers require a good understanding of spelling syntax in a language (such as English).

• You simply write the letter which has been added or omitted or switched around.

• Whenever there is a switched spelling mistake you take the first letter of the switched word.

Congratuatoins on your pronotion. I hope it ddoes pay well enugh. I am gettig a bbeautiful renovated Garden right now. It will nclude the new fountain I madde back a while aggo and I'm extrmly happy about this!

## Spelling (mistake) cipher

• Spelling ciphers require a good understanding of spelling syntax in a language (such as English).

• You simply write the letter which has been added or omitted or switched around.

• Whenever there is a switched spelling mistake you take the first letter of the switched word.

Congratuatoins on your pronotion. I hope it ddoes pay well enugh. I am gettig a

bbeautiful renovated garrden right now. It will nclude the new fountain I madde

back a while aggo and I'm extrmly happy about this!

London Bridge

L

N

O

D

O

N

B

R

I

D

G

E

## Encryption is about being able to share safely

• During World War II encryption and decryption were very big parts of everyday battles to ensure that the enemy did not manage to get hold of vital information.

• The Germans invented a machine called an Enigma machine that was used to encipher and decipher messages.

## Encryption is about being able to share safely

• During World War II encryption and decryption were very big parts of everyday battles to ensure that the enemy did not manage to get hold of vital information.

• The Germans invented a machine called an Enigma machine that was used to encipher and decipher messages.

• It is said that the war was shorted by several years thanks to Alan Turing's breaking of Enigma.

## The world wide web

• Have you ever noticed the little padlock at the top of the browser?

• Most of the world’s websites are now encrypted using public and private key encryption. We are not going to go into too much detail about this, however.
• In a nutshell, all that public key and private key encryption means is that all the data transmitted between the user’s web browser and the web server is encrypted.

• Browser cookies are small pieces of data that websites send and receive to and from the computer that has requested the website. They contain small amounts of data such as preferences or settings.

• Cookies can be used to track a computer system by adding a small piece of data that uniquely identifies the computer system (not the user). These cookies are known as tracking cookies.

• These tracking cookies can then figure out things about the user such as the pages they visit on the website (although there are other ways for them to do this, so disabling cookies does not prevent the user being tracked), their interests and the computer system being used.

Your job is to encrypt a message that is up to 15 characters long using a Caesar cipher. Use a shift that you think is suitable.

Pass your message on to the next person but make sure to tell them the first letter of your message.

Now using the first letter, figure out the shift and then the message.

Presentation Overview
Encryption
© 2020 - 2024 J Balfour
19:38 | 23-05-2024
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