1. Introduction to Cryptography and Secure Communications  What is cryptography?  Encryption  Decryption

2. Key Terminology  Plain text  Example: “Hello”  Cipher text  Example: “Ifmmp”  Encryption  Example: Replace each letter with the next letter of the alphabet  Decryption  Example: Replace each letter with the previous alphabetical letter  Key  Example: a=b, m=n

3. How would you break this code? 20-15-4-1-25 25-15-21 23-9-12-12 12-5-1-18-14 1-2-15-21-20 3-15-4-5-19

4. Cipher Text 20-15-4-1-25 25-15-21 23-9-12-12 12-5-1-18-14 1-2-15-21-20 3-15-4-5-19 ● Cipher text ● Text that has been transformed into an unreadable format. ● Code ● In cryptology, code means substituting a meaningful word or phrase with another word or phrase to change or hide meaning Copyright ETPRO 2010

5. Early Cryptology O Low literacy rates O Greek “scytale” O Translational methods O The Caesar Cipher

6. Monoalphabetic Ciphers O Specific O Consistent O Single letter to letter change O Easy to break

7. Caesar Cipher

8. Caesar Cipher –Shift of 7 ● Encrypt this message using the Caesar shifter- Shifting 7 ● ROME IS THE GREATEST EMPIRE. ● Decode this message ● YVTL DHZ UVA IBPSA PU H KHF. English Coded

9. Answers ● Correct Code =YVTL PZ AOL NYLHALZA LTWPYL. ● Decoded message = Rome was not built in a day.

10. Early Cryptology - Problems O Frequency Finger Prints

11. Using the Frequency Table Decode this Message TFNRIUJ UZV DREP KZDVJ SVWFIV KYVZI UVRKYJ; KYV MRCZREK EVMVI KRJKV FW UVRKY SLK FETV.

12. Try one on your own ● Encode a “common” message using the Caesar Cipher and any shift you choose and exchange the ciphertext with a classmate. ● The student receiving the ciphertext should decode the message and be able to tell what shift was used.

13. Modern Era Cryptography O WWII cryptography O German Lorenz Cipher machine O Rare languages used O Computer’s effect on cryptography

14. Modern Cryptography

15. Cryptography and You  How does cryptography affect your life?  What might happen if we did not have the protection it provides?  What makes codes harder to break?  How does math affect your life?