1. Topic 3: Data
Encryption

2. Encryption
Sometimes, we may want to keep our data hidden from unwanted attention
Sending secret messages to someone
Keeping private data secure
Stopping people online seeing sensitive data (like bank account details or passwords)
Turning data in its original form into something harder to understand is called encryption

3. Encryption In encryption, there are a few important terms to learn:
Plaintext: the data in its original, easily understandable form
Cipher text: the data in its encrypted, harder to understand form
Cipher: the technique used to encrypt the data (plaintext  cipher text)
There are lots of ciphers out there, each involving different steps

4. Encryption We will look at four ciphers in total
Pigpen Cipher
Caesar Cipher
Vigenere Fence
Rail Fence Cipher
They each vary in terms of complexity
Making some ciphers easier to use than others

5. Encryption: Pigpen Cipher
First up we have the Pigpen Cipher
Also known as the Freemasons Cipher
Involves writing each letter in the alphabet in a series of grids
They have to be written in the same order every time

6. Encryption: Pigpen Cipher
To encrypt some plaintext, we replace each character with the area it’s in within the given grid
To decrypt, we simple work backwards
A 
N 
S 
W 

7. ENCRYPTING THINGS IS FUN
Encrypt the following phrases using the Pigpen Cipher
HELLO WORLD
THIS IS A MESSAGE
ENCRYPTING THINGS IS FUN

8. Encryption: Caesar Cipher
Let’s move over to the Caesar Cipher
Also known as the shift cipher
Involves moving individual letters so many spaces along
Shifting them
This creates the cipher text
To decrypt, move the letters in the opposite direction
Move the same number of spaces
The shift used is called the key
Take a look at this virtual Caesar Cipher wheel!

9. Encryption: Caesar Cipher
Example
Plaintext: TIM IS THE COOLEST
Cipher Text: XMQ MW XLI GSSPIWX
What shift was used here?

10. Using the keys listed in the table below, encrypt and decrypt the following texts
Use the Caesar Cipher
Task
Key
Text
Encrypt 15
I AM GOING TO BE A SECRET 7
I WILL NEVER BE KNOWN 17
DOGS ARE CUTE I GUESS
Decrypt 6
G RKBKR OY ZNK HKYZ 4
IRGVCTXMSR MW XSXEPPC JYR 10
S KW RKFSXQ DRO WYCD PEX

11. Encryption: Vigenere Cipher
Now we’re on to the Vigenere Cipher
Similar to the Caesar Cipher
However, uses a phrase (not a key)
This phrase acts as the key for encryption
We calculate a number for every letter in the phrase
Shift individual letters in the plaintext by that amount
Loop back to start of phrase when reaching the end of it

12. Encryption: Vigenere Cipher
Example
Plaintext: WOW TIM IS COOL
Key Phrase: GCSE
Key Shifts = 6 (A  G), 2 (A  C), 18 (A  S), 4 (A  E)
Plaintext with Key Shifts:
Result: CQOXOOAWIQGP W O T I M S C L 6 2 18 4

13. ENCRYPTING THINGS IS FUN
Use this passphrase to encrypt the following plaintext: IGCSE
HELLO WORLD
THIS IS A MESSAGE
ENCRYPTING THINGS IS FUN

14. Encryption: Rail Fence Cipher
The final cipher we’ll look at is the Rail Fence Cipher
A transposition cipher like Caesar and Vigenere
Involves writing the plaintext down/up rows
The key is how many rows we use H O L E W R D

15. Encryption: Rail Fence Cipher
Here we are encrypting the plaintext HELLO WORLD
With a key of 3, we write the plaintext along three rows
Moving on to a new row each time H O L E W R D

16. Encryption: Rail Fence Cipher
To get the cipher text, we write the rows from top to bottom H O L E W R D
Result: HOLELWRDLO

17. ENCRYPTING THINGS IS FUN
Use a key of 4 (and the Rail Fence Cipher) to encrypt the following phrases:
HELLO WORLD
THIS IS A MESSAGE
ENCRYPTING THINGS IS FUN