A banking app uses Diffie-Hellman key exchange to let customers securely transfer money. Here’s how it works:

1. Customer and Bank publicly agree on: 
   Prime and base . 
2. Customer picks a private secret (e.g., ), computes mod p mod 23 , and sends A to the Bank. 
3. Bank picks a private secret (e.g., ), computes mod p mod 23 , and sends B to the Customer. 
4. Both compute a shared secret key to encrypt the transaction: 
   Customer: mod p mod 23
   Bank: mod p mod 23 \)= 18 

An attacker intercepts the public messages and impersonates the Bank to trick the Customer into sending money to the attacker’s account. 

Why can an attacker impersonate the Bank without knowing any private secrets?