I have this lecture slide. I am hoping someone can take me through line by line of how it works, because I cannot understand the a to the power of -1 part.
So far I have
Key(3,5). EncLetter((3,5), 7) = 3 * 7 + 5 mod 26 = 0 DecLetter((3,5),0) = ???? * (0-5) mod 26 = ???
I need to calculate an inverse or something, but I have no idea.
From the comments it appears that I am very wrong. If someone could please provide a step by step instruction with how to calculate this I would be eternally grateful.