# Multi-Stage Quantum Secure Direct Communication Using Secure Shared Authentication Key
## 5 Example of the Proposed Protocol
### Security Check Procedure
The channel loss will lead to photon loss, which results in the secret information loss due to the information been encoded into individual photons. In addition, an eavesdropper could hide her presence in the channel noise and take the advantages to gain a certainamount of information [6]. Thus, a quantum error correction is necessary during transmission via a noisy channel. ## 8 Conclusions

This work implements a secure mutual authentication to ensure the legitimacy of users without any involvement of the third party. Unlike the most well-known QSDC protocols that rely on a slight classical communication to share the pre-shared authentication key at the onset of communication, the proposed protocol fully utilizes the quantum channel to share the secret angle and authentication key at the initial stage of authentication. Firstly, the proposed scheme is enhanced with ITT implementation by allowing the sender to detect any disturbance by the third party. When quantum particles pass through optical polarization devices at the sender's site, and an eavesdropper is present in the communication to read the photon, the response by the receiver might induce additional time. Secondly, Pauli-X quantum gate operation is employed where the received qubit is flipped according to the numerical secret rotation angle to increase the difficulty for [PERSON] to steal the information. The proposed protocol can be concluded that public communication or public states are not used to transmit a secret message or verify the parties. The security of the proposed scheme is discussed in the context of eavesdropping attacks during initial authentication and transmission of messages. Security analysis of initial authentication and transmission of messages has shown that the eavesdropper is unable to reveal any information about the authentication key or the transmitted message. That is because [PERSON] only knows the secret angle of polarization and authentication key, and this is successfully shared with [PERSON] through the quantum channel without being exposed to [PERSON]. The authentication is also prepared before the message is exchanged, and bit-by-bit checks are performed during quantum communication. The security analysis demonstrates that the suggested quantum authentication scheme is secure against most of the well-known attacks. There is no chance [PERSON] could impersonate either [PERSON] or [PERSON]. In the proposed protocol, we only considered two parties involved in the communication. Recently, the authors of [35] proposed an effective way to share the authentication key among three parties using a single photon in polarization and spatial-mode degree of freedom. Following their work, we will study the authentication parts of three-party on multi-stage using unitary transformation of QSDC in the future. The problem of photon loss in the real implementation of the QSDC protocol has been studied in our work [14]. Therefore, the implementation of practical QSDC in a realistic environment of high information loss and noise using the proposed protocol should be focused on in our future research. Investigation, N.Z.H. ; Methodology, N.Z.H. ; Supervision, Z.A.Z., Z.M.H. and I.A. ; Validation, Z.A.Z., Z.M.H. and I.A. ; Writing--original draft, N.Z.H. ; Writing--review & editing, Z.A.Z., Z.M.H. and I.A. All authors have read and agreed to the published version of the manuscript. This research is sponsored by University Putra Malaysia. The authors declare no conflict of interest. ## References

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