Teleportation attack on the QSDC protocol with a random basis and order

The quantum secure direct communication (QSDC) protocol with arandom basis and order is analysed and an effective attack, i.e.teleportation attack, is presented. An eavesdropper can obtain halfof the transmitted secret bits with the help of this special attack.It is shown that quantum teleportation can be employed to weaken therole of the order-rearrangement encryption at least in a certaincircumstance. Meanwhile, a possible improvement on this protocol isproposed, which makes it secure against this kind of attack.