Question

Can anyone help me with the cryptology in math?

Answer 1

@myininaya

Answer 2

cryptology = @myininaya

Answer 3

Post your problems, still.

Answer 4

I need help decryption the Affine Cipher.

Answer 5

I am not sure if this is what you are looking for but if I wanted to crack any substitution encryption I would just mark down the frequency of the characters in the message then compare the frequency to a the frequency of letters in the alphabet. Is this what you mean? http://en.wikipedia.org/wiki/Letter_frequency you could use the charts on there to solve it.

Answer 6

The affine cipher is a monoalphabetic substitution cipher isn't it?

Answer 7

I believe frequency analysis is your first step. You need to find at least 2 letters that way then you have to solve a system of equations I think.

Answer 8

Did they give you any letters?

Answer 9

So for my encryption, I did E(X)=(5x+8) mod 26 for the encryption key and I made N=13. I encrypted it, making it 21 or W. I know the Decryption formula is D(Y)=21(y-8) mod 26, but I'm not sure how to find the decryption function.

Answer 10

So you want to find the decryption function for the affine cipher where e(m)=5x+8 mod 26 correct?

Answer 11

yepp

Answer 12

Alright. Fortunately, \(\gcd(5, 26)=1\) so we can actually make a decryption function. Basically, to get the decryption function, take the encryption function and solve for x. So you should get \[c\equiv5x+8 \pmod{26}\]\[c-8\equiv 5x\pmod{26}\]Now, we need to find \(5^{-1}\pmod{26}\). You can solve this using the Euclidean algorithm to find that \(5^{-1}\equiv 21 \pmod{26}\). Hence, \[5^{-1}(c-8)\equiv x \pmod{26}\]\[21(c-8)\equiv x \pmod{26}\]