Affine Cypher Encryption - Decryption

Affine Cypher Encryption - Decryption

1. Affine cipher Ammar Amjad Kainat Khalid Zakriya Ali Sabir Syed Mohammad Ali Hamza Tariq Qazi Talha Hamid

2. Introduction Background

3. encoding Convert into a coded form.

4. encrypt Convert (information or data) into a cipher or code, especially to prevent unauthorized access.

5. Jean-Francois Champollion French soldier Philologist Orientalist DECIPHER of the EGYPTIAN HIEROGLYPHS

6. encryption techniqe

7. Y=( aP+k )%26

8. a=multiplier k=shift p=data

9. gcd (a,26)

10. Why 26??

11. g=6 Suppose we want to encrypt ‘g’ Checking corresponding numeric value

12. ( 7, 2) using

13. Plugging the values in formula: =(7*6+2)%26 =44%26 =18

14. as s=18 we get : ‘ g ’  ‘ s ’

15. Decryption technique

16. Y=( aP+k )%26

17. ( a , k ) KEY 

18. P=[(a^-1)(Y-k)] % 26 Here this (a^-1) is not the multiplicative inverse of a but it is the modular inverse of a.

19. a = 7 k = 2 As we had encrypted : ‘ g ’  ‘ s ’ Using :

20. ( a . a inverse) % 26 = 1 If we take : 1 <= a <= 25 ε a ^ -1 { 1,3,5,7,9,11,15,17,19,21,23,25}

21. key( a , k )=( 7,2 ) a inverse = 15 Y = 18 P = [a inverse ( Y – k) ] % 26 P = [ 15 ( 18 - 2 ) ] % 26 P = 6

22. key( a , k )=( 7,2 ) a inverse = 15 Y = 18 P = [a inverse ( Y – k) ] % 26 P = [ 15 ( 18 - 2 ) ] % 26 P = 6 Its CORRECT !

23. Algorithm & code

24. Flow-Chart PROCESS OF ENCRYPTION PROCESS OF DECRYPTION

25. START TAKE INPUT FROM USER CONVERT ALPHABETS TO NUMBERS ENCRYPT NUMBERS

26. CONVERT ENCRYPTED NUMBERS TO LETTERS CONVERT LETTERS BACK TO NUMBERS DECRYPT NUMBERS CONVERT NUMBERS TO LETTERS END

27. limitations Case of the alphabets Spaces Shift Multiplier

28. conclusion Thank-you!