1. Lesson Objectives Aims You should know about: 1.3.1:
(c) Symmetric and asymmetric encryption.

2.
Just to prove a point…

3. Did you do the reading?

6. Hashing - Summary Maps data/bits to a unique string (hash)
The smallest change to source data results in large hash changes
One way function
Goal to avoid collisions, but collisions are always possible (collision = two or more inputs giving the same output)
Quick to calculate the hash
Output is always the same size for a given algorithm, smaller than input

7. Encryption
“To be honest, the spooks love PGP,” Nicholas Weaver, a researcher at the International Computer Science Institute, told the Usenix Enigma conference in San Francisco. “It's really chatty and it gives them a lot of metadata and communication records. PGP is the NSA's friend.”

8. Encryption
A two way process in which data is scrambled as to make it meaningless without a key
Only key holders should be able to encode and decode data
Encrypted messages are said to be “cypher text”

9. Encryption The government would love easy access to your information…
Encryption is a very hot topic at present – also covered later in the course in Ethics (so read the news…)
It could be argued that computing would not have developed without war and…the need for secret communications
…and breaking those communications

10. Symmetric encryption:
Data is encoded using a given method
Data is decrypted using the exact reverse of that method
Very quick to set up and easy to use
Prone to cracking/brute force

11. Asymmetric encryption
Data is encrypted using a key…
…and decrypted using a different key
This means:
Both keys would be needed to encrypt and decrypt intercepted messages
Much more difficult to crack/brute force
Usually known as Public Key Encryption

12. Recipient publishes their public key:
PKE
Recipient keeps their private key safe, this will be used to UNLOCK the data when it arrives
Recipient publishes their public key:
The sender (and anyone else) can encrypt using this (but that’s ok, right?)
But it is one way, so cannot be used to decrypt
When data arrives, the private key unlocks the data (only known to recipient)

14. Try it out – method a)
Encode a message and look at the output
Encode the SAME message twice – look at the output.

15. Now try this… Method b)
Encrypt the same message again – what do you notice?
Try the same message again – what do you notice?

16. What other popular encryption methods are there?
Questions
What kind of encryption is method a using?
What kind of encryption is method b?
What are the differences in the outputs?
One of the methods is AES encryption, make notes on:
What it is
How it works
How secure it is :
What other popular encryption methods are there?

17. Review/Success Criteria