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# Cryptography by Epul

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### Cryptography by Epul

1. 1. @agatestudio Cryptography M Saepul Knight Agate Studio
2. 2. M. Saepul Ramdani Cryptography
3. 3. What is …  Crypto = secret  Graph = writing Or Cryptology = science of secret
4. 4. Alice Bob M Chester Alice and Bob are communicating via insecure channel (nguping)
5. 5. How  We need “machine” or “function”  To modify original message to cipher text.  And then…  We need a “secret”, we need key
6. 6. More details  Encryption  E (m, k) = c;  Decryption  D (c, k) = m; D ( E ( m, k ), k ) = m
7. 7. Alice Bob c Chester Alice and Bob are communicating via insecure channel (nguping) E (m, k1) = c D (c, k2) = m
8. 8. Example  Vigenère cipher TheVigenère cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword. It is a simple form of polyalphabetic substitution.
9. 9. Vigenère cipher Example: m = Z k = S c = R m :AGATE k : MLAML c : MRAFP
10. 10. Burial at the sea
11. 11. Periodic table
12. 12. There’s nothing to do with that chemical structure  (But we need look at the atomic numbers)  Sc-Sc-Ti-P-Li-Cl-Na-Mg-P-Be-Mg  21-21-22-15-3-17-11-12-15-4-12  U-U-V-O-C-Q-K-L-O-D-L  Remember theVigenère cipher!  And also, we have SUCHONG as key  Why SUCHONG ? Because you should never underestimate the fallibility of an egomaniac
13. 13. Next? U-U-V-O-C-Q-K-L-O-D-L S-U-C-H-O-N-G-S-U-C-H C-A-T-H-O-D-E-T-U-B-E CathodeTube NB:Actually, that wasn’t good implementation
14. 14. When we start use our implementation?  We won’t and we mustn’t  Because, we need a secure cipher which proven by the expert mathematically and statistically  Unless, we do it for fun or learning
15. 15. Perfect but impractical  The cipher called perfect when there’s no clue/information about key or message on cipher text  Why impractical ? (We will discuss it after next slide)
16. 16. One Time Pad  Use XOR operation 1 ^ 1 = 0 1 ^ 0 = 1 0 ^ 1 = 1 0 ^ 0 = 0  Quiz: z = x ^ y ^ x; z = ?  z = y (whether value x and y)  M ^ K = C
17. 17. … back to impractical  One time pad is a perfect cipher  As long:|k| >= |M|
18. 18. Closure  Next time, we’ll discuss more about keys, modern cipher, how it works, how we use it etc.  Uh… Question, anyone ?  Thank you 