Controlled Secure Quantum Dialogue Using a Pure Entangled GHZ States

We present a controlled secure quantum dialogue protocolusing a non-maximally (pure) entangled Greenberger-Horne-Zeibinger(GHZ) states at first, andthen discuss the requirements for a real quantum dialogue. We showthat the authorized two users can exchange their secret messagesafter purifying the non-maximally entangled GHZ states quantumchannel unconditionally securely and simultaneously under thecontrol of a third party.