1. The Evolution of Secret Writing 郭謹瑋 b9202053 黃聖德 b9202074 葉人豪 b9202078 謝東頤 b9202095

2. 流程 Introduction ＆ earliest history ： barrydog Steganography ＆ cryptography ： VOYAGE Transposition ： abchoas Substitution ： bush

3. Speaking of code … movie ： Mercury Rising 、 Infernal affairs （ MORSE code ） novel ： Sherlock Holmes cartoon ： Conan The communication during war or between lovers etc…. Maybe now you would like to know: the evolution of secret writing

4. The earliest history According to the father of history ： Herodotus The conflicts between Greece and Persia The art of secret writing saved Greece from being conquered by Xerxes, king of kings, leader of Persians. This is what happened during the time of Xerxes, the Xerxes who ruled over 127 provinces stretching from India to Cush （ Esther 1:1,From Bible ）

5. The earliest history Demaratus (Who wanted to notify Sparta and Athen Xerxes intended to invade Greece ) ： 1.scraping the wax off a pair of wooden folding tablets 2.writing on the wood 3.covering the message over with wax again.

6. Another example ： Histaiaeus He wanted to encourage Aristagoras of Miletus to revolt against the Persian king. Way of secret writing ： 1.shave the head of a messenger 2.The message on his scalp

7. One day, if you are a “CIA Agent”

8. First: Hide your message steganography it means that use many ways to make your enemy can not find your message It is derived from Greek words steganos, meaning ”covered,” and graphein, meaning ”to write.”

9. For example 1.The chinese wrote messages on fine silk, which was scrunched into a tiny ball and covered in wax. Then the messenger would swallow the ball of the wax Writing in the invisible ink for example: milk, organic fruit because they all are rich in carbon and therefore char easisy.

10. But …… If the message is still found by your enemy, they will know everything…… So we need to find other way to hide not only the existence of the message but its meaning

11. Second: hide the meaning Cryptography It means use many kind of ways to make the meaning of your message hidden. It is derived from the Greek word kryptos, meaning “hidden”

12. How to The message is scrambled according to a particular protocol which is agreed beforehand between the sender and the intended recipient Thus the recipient can reverse the scrambling protocol and make the message comprehensible

13. What Is Transposition ? Rearranged letters (Anagram) Ex. “Now” & “Eat” Security v.s Difficult Random Transposition “Tea” v.s “I saw my doctor this morning. ” → There are 23! distinct arrangements. Now → Won, Onw, Wno ； Eat→Tea

14. Unscrambling System(1) Rail fence ： THY SECRET IS THY PRISONER; IF THOU LET IT GO, THOU ART A PRISONER TO IT ↓ T Y E R T S H P I O E T O L T T O H U R A R S N R O T H S C E I T Y R S N R F H U E I G T O A T P I O E T I ↓ TYERTSHPIOEITOLTTOHURARSNRQTHSCEITYRSNRFHUEIGTOATPIOETI

15. Unscrambling System(2)

16. Cryptography--Substitution Caesar Code In transposition each letter retains its identity but changes its position, whereas in substitution each letter changes its identity but retains its position.

17. When we substitute on character for another to conceal the original, we are using a substitution cipher. The oldest is one used by Julius Caesar, who added 3 to each of his letter numbers to conceal the real message. For example ： Using the Caesar cipher, from "Hello", we get: "khoor"

18. Caesar ’ s Cipher with a Keyword Because it is difficult to remember an incoherent string of 26 letters, cipher alphabets are often based on a single word that is easy to memorize. The simplest method is to write out the keyword, omitting any repeated letters, then to follow it with the remaining letters of the alphabet in order. Here is a Substitution Cipher with zebra lips as the keyword.

19. To sum up ……