A hospital uses an RSA-based system to send encrypted patient status updates to doctors' pagers. The system encrypts short messages like "STABLE" or "CRITICAL" using textbook RSA: 

1. Convert each letter to a number . 
2. Encrypt the number: mod n.
3. An attacker intercepts encrypted messages and notices that: 
   The message "STABLE" always encrypts to the same ciphertext:  
   . 
   The message "CRITICAL" always encrypts to the same ciphertext:  
   . 

Why is this "same message → same ciphertext" behaviour a serious security flaw in real-world systems?