Quantum steganography that utilizes the quantum mechanical effect to achieve the purpose of information hiding is a popular topic of quantum information.Recently,El Allati et al.proposed a new quantum steganography using the GHZ4 state.Since all of the 8 groups of unitary transformations used in the secret message encoding rule change the GHZ4 state into 6 instead of 8 different quantum states when the global phase is not considered,we point out that a 2-bit instead of a 3-bit secret message can be encoded by one group of the given unitary transformations.To encode a 3-bit secret message by performing a group of unitary transformations on the GHZ4 state,we give another 8 groups of unitary transformations that can change the GHZ4 state into 8 different quantum states.Due to the symmetry of the GHZ4 state,all the possible 16 groups of unitary transformations change the GHZ4 state into 8 different quantum states,so the improved protocol achieves a high efficiency.
Recently,some blind quantum signature(BQS) protocols have been proposed.But the previous schemes have security and efficiency problems.Based on the entangled Greenberger-Horne-Zeilinger(GHZ) states,a new weak BQS protocol is proposed.Compared with some existing schemes,our protocol has 100% efficiency.Besides,the protocol is simple and easy to implement.The security of the protocol is guaranteed by the correlation of the GHZ particles held by each participant.In our protocol,the signatory is kept blind from the content of the message.According to the security analysis,the signatory cannot disavowal his/her signature while the signature cannot be forged by others.
In this paper,we first propose a hidden rule among the secure message,the initial tensor product of two Bell states and the final tensor product when respectively applying local unitary transformations to the first particle of the two initial Bell states,and then present a high-efficiency quantum steganography protocol under the control of the hidden rule.In the proposed quantum steganography scheme,a hidden channel is established to transfer a secret message within any quantum secure direct communication(QSDC) scheme that is based on 2-level quantum states and unitary transformations.The secret message hiding/unhiding process is linked with the QSDC process only by unitary transformations.To accurately describe the capacity of a steganography scheme,a quantitative measure,named embedding efficiency,is introduced in this paper.The performance analysis shows that the proposed steganography scheme achieves a high efficiency as well as a good imperceptibility.Moreover,it is shown that this scheme can resist all serious attacks including the intercept-resend attack,measurement-resend attack,auxiliary particle attack and even the Denial of Service attack.To improve the efficiency of the proposed scheme,the hidden rule is extended based on the tensor product of multiple Bell states.
