A theoretical scheme for controlled and secure direct communication is
proposed. The communication is based on GHZ state and controlled quantum
teleportation. After insuring the security of the quantum channel (a set of
qubits in the GHZ state), Alice encodes the secret message directly on a
sequence of particle states and transmits them to Bob supervised by Charlie
using controlled quantum teleportation. Bob can read out the encoded messages
directly by the measurement on his qubits. In this scheme, the controlled
quantum teleportation transmits Alice's message without revealing any
information to a potential eavesdropper. Because there is not a transmission of
the qubit carrying the secret messages between Alice and Bob in the public
channel, it is completely secure for controlled and direct secret communication
if perfect quantum channel is used. The feature of this scheme is that the
communication between two sides depends on the agreement of the third side.Comment: 4 pages, no figur