1. Enigma, Cyphers and Encryption
How do computers communicate securely and secretly?

2. Caesar Cypher h e l o a b c d e f g h i j k l m n o p q r s t u v w xz h e l o
Key
a to h

3. How could we improve on this?

4. Caesar Cypher h e l o
Secret key
a to h

5. How could we improve on this?

6. Caesar Cypher – plus 1 h e l o o l r u +1
Move inside rotor once clockwise at the beginning of each move h e l o  o l  r  u  +1
Secret key
a to h
Move 1

7. How could we improve on this?

8. More rotors

9. The Prinigma machine

10. Prinigma
“ By making our own prinigma machine it was easy to understand something that was so hard to invent in the first place.”
Y6 St George’s

11. Prinigma Three rotors h e l o
“It was fun to build my own machine and the videos were interesting, especially seeing the original machines. I wish I had had more time to crack codes.” Y6 St George’s h e l o
Secret key
Reflector B
Q, E, V, A

12. How could we improve on this?

13. Prinigma Three wheels Move right rotor once each time at the start h e
Three wheels
Move right rotor once each time at the start
“It was really cool to see how the enigma machine worked and how it was used. It was fun that we could upcycle something to make our own technology.”
Y6 St George’s
Secret key
Q, E, V, A
Move 1

14. How could we improve on this?

15. Cypher and Encryption

16. Where do we see encryption?
Connections with learning

17. Common letters
Do different languages have different frequent letters? English - e t a o i n s h r d l u Polish -

18. Public and Private keys?
A tells you where there is place you can safely put your information – PUBLIC KEY B posts his code – PRIVATE KEY Only A can open box and find the PRIVATE KEY for B

19. In reality – AES (Advanced Encryption Standard) algorithm
Bob chooses two very large (distinct) prime numbers p and q;
n=pq , m= lcm {p−1 , q−1 } (lcm is the least common multiple );
Bob chooses r , where r>1 and r is coprime with m (i.e. r and m have no factors in common);
Bob then finds the unique s such that rs≡1(mod m)
Bob now tells everyone what n and r are, but does NOT say what p, q or s are.
Alice wants to send the message M (a single number) where M and n are coprime and 0<M<n.
Alice finds Mc , where Mc≡Mr(mod n) , and sends the message Mc to Bob.
Bob receives the message Mc from Alice and decodes it.
Now Bob knows p, q, m, n, r, s , and he uses these to decode the message Mc from Alice so as to find M . To do this Bob uses the theorem that (Mc)s≡M(mod n)

20. Playing with primes
What is the largest prime under 100? What is the largest prime under 1000? What is the largest prime under 10000? What is the largest prime under ? Can you write an algorithm to find these? Can you program this?

21. Playing with Factors Think of the factors of: 12 120 1200 12000 120000

22. Websites

23. Wireless connections WPA2 – Wi-Fi Protected Access 2
AES – Advanced Encryption Standard
Do your children know how to set up a secure link?

24. WhatsApp Provides encrypted communication

25. Internet of Things
How far are we going to allow the ease of use to question our privacy or state intervention?
Smart speakers?
Self driving cars?