I am somewhat new to Cryptography and I'm struggling with this proof I came across in my Intro to Cryptography course. I understand the proof of security for a one-time pad:
Pr[M = m | C = c] = Pr[M = m| C = c] * Pr[M = m] / Pr[C = c] = (1/2^n) * Pr[M = m] / (1/2^n) = Pr[M = m]
I was wondering what happens if m > n? Pr[M = m|C = c] != Pr[C = c] but I want to know why and exactly what values these probabilities acquire.