Answer
The most common letter in the ciphertext is X.
In typical English text, the most common letter is E.
The position of E in the alphabet is 4 .
The position of X in the alphabet is 23.
Calculate the shift key k :
k=(X−E)mod26=(23−4)mod26=19
Work Step by Step
X is the most common letter in the ciphertext, we say that E in the plaintext has been shifted to X in the ciphertext. Now need to calculate how much E was shifted to become X to find the value of
𝑘.
