1. Cryptography
CS Principles
January 19, 2017

2. Needs for Privacy
What are some specific needs for privacy when using the internet?

3. Information Security for…
Defending against external/internal hackers
Defending against industrial espionage
Securing E-commerce
Securing bank accounts/electronic transfers
Securing intellectual property
Avoiding liability
Pervasiveness of /networks
Online storage of sensitive information
Insecure technologies (e.g. wireless)
Trend towards paperless society
Weak legal protection of privacy

4. Sharing secrets activity
Find out the average GPA of THE PEOPLE in your group without anyone telling their GPA

5. History 50 B.C. Julius Caesar uses cryptographic technique
400 A.D. Kama Sutra in India mentions
cryptographic techniques
1250 British monk Roger Bacon
describes simple ciphers
1466 Leon Alberti develops a cipher
disk
1861 Union forces use a cipher during Civil War

6. History 1914 World War I – British, French, and
German forces use encryption
technology
1917 William Friedman, Father of U.S.
encryption efforts starts a school
for teaching cryptanalysis in
Illinois
1917 AT&T employee Gilbert Vernam
invents polyalphabetic cipher
1919 Germans develop the Engima machine
for encryption

7. History 1937 Japanese design the Purple machine for encryption
1942 Navajo windtalkers help with secure
communication during World War II
1948 Claude Shannon develops statistical
methods for encryption/decryption
1976 IBM develops DES
1976 Diffie – Hellman develop public key /
private key cryptography
1977 Rivest – Shamir – Adleman develop the
RSA algorithm for public key / private key

8. 50 B.C. Julius Caesar uses cryptographic technique
Make your cipher wheel

9. Practice encoding and decoding
HELP (ROT 6) -> NKRV Encoding
NKRV -> HELP Decoding
Decide on a encoding (ROTx) and encode a 2 word message. Exchange messages with someone at a different table and decode.

10. Substitution Cipher HAPPY wednesday What does this mean?
LETTC AIHRIWHEC
Is this easier?
JCRRA YGFPGUFCA
HAPPY wednesday

11. Caesar Cipher
A substitution cipher where each plaintext letters is replaced by some letter a fixed number spaces down in the alphabet

12. ROT13 Network data encryption / decryption using ROT13 algorithm
Rotates characters by 13 places
‘A’  ‘N’, ‘M’  ‘Z’, ‘a’  ‘n’, ‘m’  ‘z’
Encryption Example:
‘Hello World’ encrypts to ‘Uryyb Jbeyq’
Decryption Example:
‘Uryyb Jbeyq’ decrypts to ‘Hello World’

13. Implementing ROT13 Consider the following four cases
IF (ch >= ‘A’) && (ch <= ‘M’)
Rotate “Right” ch by 13 characters
IF (ch >= ‘N’) && (ch <= ‘Z’)
Rotate “Left” ch by 13 characters
IF (ch >= ‘a’) && (ch <= ‘m’)
IF (ch >= ‘n’) && (ch <= ‘z’)

14. 1919 Germans develop the Engima machine for encryption
Enigma video
Enigma simulator

15. Alice 3 Assignment Implement a caesar cipher in alice 3
Have a character say something in code and then decode it later in the animation
Make it interactive allowing the user to input text and encode/decode the text
Anything else

16. Interactivity in alice 3
Create events in “Edit Code” mode