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.
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
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. 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. 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. … back to impractical
One time pad is a perfect cipher
As long:|k| >= |M|
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