I am not sure how to get the key for the following Monoalphabetic Cipher question. This is a textbook question and I know the answer, but I juts dont know how they got the key.
Question:
Decrypt the following Cipher texts, and give the key. (Note that the correct key is the Encryption key, so if F changes to H and F is the plaintext, then the key is “C”):
(a) YRRYAIYRMLAC (b) DOBXQPZELLI
Answer: a) Text:ATTACKATONCE
Key = X
b) Text: GREATSCHOOL
Key = A
Can somone please explain to me how to determine the key?