I came across this riddle link question:
Your name's Graham.
Bob wanted to send Alice a secret msg m. However, he was concerned about the security. He encrypted his message with a keyword that both of them knew. Several weeks before this, you overheard them exchanging the keyword k = 'EZRA'. Now, Bob has asked you to deliver the letter to Alice. You want to find out what's the letter about. Decrpyt the secret message m using the ciphertext c='MEDMTBJBMAE'.
The answer to this question was
HELLO GRAHAM. How could one deduce that without knowing the answer of course.
What can we deduce from the keyword EZRA?