# Ciphers and Modular?

How to answer a and b, I have no idea how to do this question. Please help!!!

### 1 Answer

- AlanLv 78 months agoFavorite Answer
So this gives the following encoding

0 3

1 12

2 21

3 4

4 13

5 22

6 5

7 14

8 23

9 6

10 15

11 24

12 7

13 16

14 25

15 8

16 17

17 0

18 9

19 18

20 1

21 10

22 19

23 2

24 11

25 20

26 3

C = (9p+3) -26k where k is based how big (9p+3)

D(C) = (aC + b) -26k

so you know (0,17) is point pair

17 = b-26k

so 1st let's hope this is for k = 0

then , check next point (1,20)

P = aC + 17-26k

20 = a + 17-26k

3 = a-26k

so if we are lucky again this is k = 0

so try

D(c) = 3c + 17 (mod 26 )

try it for all values and see that it works

That is, it maps all encoded values back to their original values.

otherwise, we would have to check so

of the other possible k values.

D = 3c +17 (mod 26)

so a = 3 and b =17

now for next part

GZQ is 6 , 25, 16

1st Char = 3*6 + 17 mod 26

1st Char = 35 mod 26

1st char = 9 a "J"

2nd char = 3*25 +17 mod 26

2nd char = 14 an "O"

3rd char = 16*3 +17 mod 26

3rd char = 13 at "N"

answer "JON"

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