1. GCSE COMPUTER SCIENCE
Topic 3 - Data
3.10 Encryption

2. Write all parts of this definition of encryption in your book.
What is Encryption?
Encryption allows data to be kept secret and secure so no one else can make use of it.
A key is used to encrypt plain text into meaningless cipher text, the same key is used to decrypt the data back into its original form.
Only someone who knows the key can decrypt the cipher. If you don’t have the key you need to crack the code.
ACTIVITY
Write all parts of this definition of encryption in your book.

3. Why do we need Encryption?
Ever since humans have been able to write, encryption has been used to make writing secret.
The Egyptians changed hieroglyphics so that the general public could not understand them.
The Romans took it to the next level by creating codes for their writing.
ACTIVITY
Write all parts of this in your book.

4. WKH WUHDVXUH LV KLGGHQ XQGHU WKH SDOP WUHH
Activity
Decrypt this message
Message
Decrypted Message
WKH WUHDVXUH LV KLGGHQ XQGHU WKH SDOP WUHH
Hint H = E and W = T
THE TREASURE IS HIDDEN UNDER THE PALM TREE
HINT
Write out the alphabet on one line of your book, it will help!

5. Activity
Answer the following question
Question
Answer
Explain how the Caesar Cipher works
The Caesar Cipher is a method of encryption and would not be used today because it is so easy to crack. The letters of the alphabet are shifted a set number of places.
A positive shift moves the letters to the right, a negative shift moves them to the left. For example, a shift of +2 would change the letter A to a C and so on.

6. Activity You are going to create your own Caesar Cipher wheel
Follow the instructions on the hand out.
Equipment needed
2 x different colour pens, scissors and a paper fastener.

7. Use your Caesar Cipher wheel to decode and encode these messages.
Activity
Use your Caesar Cipher wheel to decode and encode these messages.
Plain text
Shift
Encrypted text
THE CAESAR CIPHER IS AN EXAMPLE OF ROMAN INGENUITY 5
YMJ HFJXFW HNUMJW NX FS JCFRUQJ TK WTRFS NSLJSZNYD
THE KEY IS HIDDEN UNDER THE FLOWERPOT 3
QEB HBV FP EFAABK RKABO QEB CILTBO MLQ