On “controlled quantum teleportation and secure direct communication”

Abstract

Based on the controlled quantum teleportation protocol, a controlled quantum secure direct communication scheme (CQSDC) protocol, which transmits a one-bit message via the Greenberger-Horne-Zeilinger entangled state, is presented by Gao et al. in [Chinese Phys. Vol. 14 (2005), No. 5, p. 893]. However, through this article we want to enlighten of the fact that, due to a flaw in the control function, receiver can reveal the whole secret message without help from the controller.