I have a frequency distribution of letters for the plaintext and the ciphertext.
I'm trying to determine the conditional probabilities to identify the plaintext/ciphertext pairings.
If I encrypt with Caesar cipher with the key of $3$, then $e$ will become $h$.
As I understand it, the conditional probability of $\Pr(M=e\mathbin|C=h)$ should be $1$ (or very close to it).
How do I calculate the conditional probability to prove that $\Pr(M=e\mathbin|C=h) = 1$?