## Wednesday, 14 June 2017

### Encryption Lesson 2 - Substitution Cipher

Substitution Cipher

Objectives and Outcomes:
• be able to explain how a substitution cipher works (band 4)
• be able to apply your understanding by creating your own substitution cipher and encoding a message (band5)

Many realised that the Caesar Cipher was weak; it was too easy to break.  The Substitution Cipher was developed to overcome this weakness.

The Substitution Cipher involved moving different letters of the alphabet around and put into a random position.

Each letter of the alphabet is replaced by another.

Your tasks
1.  On a new blog post, titled the same as this one, explain how a substitution cipher works.

2.  On a Google doc, create your cipher in the same way as I have shown you, but with different randomly placed letters.

3.  Apply your cipher by encoding the phrase 'Computer science rocks'.  Write the message and the code under your cipher table.

4.  Under this, copy my cipher from my blog.

5.  Using my cipher, decode this message: X  RXSP  OEXTXCK  BPIEPT  VPBBDKPB.

6.  Share your Google doc to 'Anyone with the link' and copy/paste the link to your post, under your first piece of writing.

7.  Explain how this cipher is better than the Caesar Cipher.

8.  Explain what senders and recipients of the coded messages would need to be able to encipher and decipher the messages accurately.

9.  How could the messages be further protected against being deciphered if intercepted regularly by others?  Write your detailed answer on your post.

Publish!