1. An Introduction to Cryptography

2. What is cryptography? noun \krip- ˈ tä-grə-fē\ : the process of writing or reading secret messages or codes “Encryption”: to put into a format that is unreadable to unauthorized individuals “Cipher”: a method of encryption, or a code

3. Basics

4. History 1900 B.C. Egyptians encoded messages on clay tablets 100 B.C. Julius Caesar uses simple encryption to send messages in wartime 1466 A.D. Leon Battista Alberti invents polyalphabetic cipher

5. 1835 Samuel Morse develops Morse Code 1940s Allies in World War II coded on enigma machines 1970s Data Encryption Standard (DES) was developed to encrypt electronic data History

6. Substitution Cipher Substitute one value for another

7. Substitution Cipher Common example: Cryptograms in newspapers

8. Substitution Cipher Original message: “plaintext”: Encrypted message: “ciphertext”

9. Solve this Substitution Cipher XKGTJDHI

10. Solution SECURITY

11. Ciphers in Popular Culture “National Treasure” (2004)

12. Keys They are what we use to secure the messages. (And to decrypt them!) They are shared to decrypt the message.

13. Keys “Asymmetric” cryptography has two keys: –Public key: used to encrypt the message –Private key: used to decrypt the message. (This one is secret) –Mathematically matched to protect the message

14. Vigenere Square Polyalphabetic cipher Column letter: plaintext Row Letter: key Example:

15. Vigenere Square Encrypt this word:

16. Solution VDOZF

17. Ciphers in Popular Culture “A Beautiful Mind” (2001)

18. Transposition Cipher Rearranges values within a block to create ciphertext Example: –“Caesar Block Cipher” –Uses 5X5 square –Message contains <25 characters Famously created by Julius Caesar!

19. Caesar Block Cipher Plaintext: LEARN ABOUT ENCRYPTION Ciphertext: L TROEA YNABEP EONT NUCI read across fill down

20. Caesar Block Cipher Try writing and encrypting your own message! Remember: <25 characters (including spaces) read across fill down Pass it to a friend to decrypt

21. Advanced Cryptography Using the types of techniques we learned, computers can encrypt files, emails, etc. –Makes communication secure –But we still need to protect our keys and passwords!

22. Advanced Cryptography Technology Example

23. Real World Application Cryptanalysts: study information systems to find hidden aspects It’s their job to decrypt messages

24. Why does this matter to you? When you put your personal information on the internet, make it hard for thieves to steal Check your passwords: http://www.passwordmeter.com/

25. Create a strong password Start with a weak password:  Linda!Marie1207 Come up with a secret key (4-6 characters)  puppy Encrypt text using the vigenere square:  Accsy!Bugxc1207 Strong Password

26. Jeopardy! What four aspects should your password include? In what profession do people break codes? Where does Gabe work? What is an encrypted message called? What cipher replaces one letter with another? What type of cryptography uses public and private keys? Who encoded messages on clay tablets? What is an unencrypted message called? What machine was used to encrypt messages in World War II?

27. Questions