Comment on "Quantum Dialogue protocol"
  In 2004, Ba An Nguyen [Phys. Lett. A 328, 6-10] has presented a Quantum Dialogue scheme for simultaneously communicating their messages. In this comment, we show that the quantum dialogue scheme is not secure against the intercept-and-resend attack and we propose a modified scheme which is secure against that attack. 
Chang-Ho Hong and Hyung-Jin Yang