Hi there, I have a homework problem where I am supposed to decrypt a Hill 2-cipher. The word I am supposed to decrypt is
XP PX RL VH
it is ciphered using digraphs on 26 letters (ignoring cases). (a=0, b=1,...,z=25)
The encryption matrix is a 2x2 matrix E.
E=(2 1)
(3 5)
The problem says that to find the decryption key, i take the inverse of matrix E in the sense of modulo 26.
i know that the message i am supposed to get in the end is
SN AP SH OT
but i am completely lost on how to take the modular inverse of a matrix.