I took a cryptanalysis class in university and I learned Caesar Cipher. But I cannot understand why frequency gives me the "key".
In a meterial, the following sentences are explained:
When Eve tabulates the frequency of letters in this ciphertext, she gets: I=14, V=13, S=12, and so on. The most common character is I with 14 occurrences. This means key = 4.
What I cannot understand is the last sentence, "This means key = 4". Most frequency alphabet is "E" which has 12.7 frequency and the number of "E" is 4 I know. But how can I compute it from the frequency? I want to totally understand this mechanism.