You have intercepted a long sequence of numbers and noticed that the
most frequently occurring numbers were 13 and 7, in this order. You
know that the ciphertext was obtained with an affine enciphering
transformation with modulus 35, on single letter message blocks of
the ordinary English alphabet A - Z and the letter b for “space”. Find
the deciphering transformation.
I have done so far:
Deciphering transformation of the form: g(y) = cx + d mod 35
Space will be the most frequently occuring, with e the second most frequently occuring.
So b or 26 ---> 13
e or 4 ----> 7
26 = g(13) = 13c + d
4 = g(7) = 7c + d
So 6c = 22 mod 35
But I have no idea where to go from here?!
Could anyone please explain?
Thanks in advance!