1. Networks
Encryption

2. Objective
To identify some of the data which should be kept secure from others.
To learn some of the ways in which data is kept secure.
To learn how unauthorised people can break ciphers and read encrypted data.
To learn about classical encryption techniques.

3. As a class, can we think of information which is secure to us?
Security
As a class, can we think of information which is secure to us?
Is there any information which you wouldn’t like other people to get their hands on?
(Discuss and make a list on the next slide) You may want to use post-its to begin with.

4. Security

5. Encryption
In order to stop people from getting our information we encrypt the information.
Data is changed so that people can no longer understand out messages. They need to have a secret key.
Have you ever tried to send a secret message to your friends or family?
You are about to decrypt a message! Use the worksheet online to find out what it says!

6. Decrypt this message

7. Terminology / Glossary
Plaintext: The original message to be encrypted
Cipher text: - The encrypted message
Encryption: - Convert the plain text into cipher
Encryption Algorithm: - The way of working out the plain text.

8. ATTACK!!!
Brute Force:
Sometimes when people are trying to get your information, they’ll try every possible key!
This is why our passwords need to be secure. They will try every possible word in the dictionary before trying every possible key combination.
An example of the brute-force attack is shown on the next slide.

9. ATTACK!!!

10. How they do it!
Our language has a footprint. It detects how many times we use letters and these are the areas they focus on. This is why we should make our passwords secure!

11. Ceaser Shift Cipher Ceaser Shift Cipher: -
Your teacher is going to show you this clip of the Ceaser Shift :
It was the earliest known substitution cipher invited by Julius Caeser.
Each letter is replaced by the letter three positions further on in the alphabet.

12. Ceaser Shift Cipher

13. Activity: -
Use the activity sheet to answer a series of questions about what you’ve learnt.
Create your own message in plain text
Create a key
Create your Cipher Text
Create a poster which includes your Cipher text and a blank space for people to solve your message.
Try to crack each others messages.

14. Extension:
Investigate the Enigma code and produce a presentation about how it was cracked.
Who helped crack it?
What was it?
Where can you find the computer today?