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In 2019, Wen et al. proposed authenticated semi-quantum key distribution (ASQKD) for identity and message using the teleportation of W states and GHZ-like states without pre-shared keys. However, the ASQKD protocol presents a vital issue in the teleportation of W states owing to its inappropriate design. Bob recovers the teleported W states without obtaining the position of the corresponding photons and then returns the recovered photons back to Alice. Hence, the teleportation of W states in Wen et al.’s ASQKD protocol was malfunctioning. Moreover, Wen et al.’s ASQKD protocol requires quantum memory, which strongly disobeys the definition of semi-quantum proposed by Boyer et al. Therefore, in this study, we discover the flaws of Wen et al.’s ASQKD protocol and propose an authenticated semi-quantum key distribution protocol. When compared to Wen et al.’s ASQKD protocol, the proposed ASQKD protocol has the following advantages: legal semi-quantum environment (i.e., does not require quantum memory), reduced quantum hardware requirement (i.e., based only on W states), does not involve classical cryptography (i.e., the hash function), and provided 1.6 times higher qubit efficiency.

In 2021, Chang et al. proposed an authenticated semi-quantum key-distribution (ASQKD) protocol using single photons and an authenticated channel. However, an eavesdropper can launch a reflective attack to forge the receiver’s identity without being detected. In addition, Chang et al.’s ASQKD protocol assumes an authenticated classical channel between the sender and the receiver. It is considered illogical to have an authenticated channel in the ASQKD protocol. If these security issues are not addressed, the ASQKD protocol will fail to deliver the secret key. Therefore, this study proposes an efficient and secure ASQKD protocol to circumvent these problems using only single photons. Security analysis proves that the proposed ASQKD protocol can effectively avoid reflecting attacks, collective attacks, and other typical attacks. Compared with the existing ASQKD protocols, this study has the following advantages: based on a single photon, it demands less advanced quantum devices, the communication efficiency is higher than most protocols, it reduces the length of the required pre-shared keys, endures reflecting attacks, collective attacks, and there is no need for the classical channel.

In 2019, Zhou et al. proposed semi-quantum identification (also known as semi-quantum authentication, SQA), which proceeds under a measure-resend and measurement-free environment. However, Zhou et al.’s SQA protocol suffers from severe information leakages. An eavesdropper can obtain an intact authentication key without being detected under this environment. In particular, Zhou et al.’s measure-resend SQA protocol is vulnerable to double CNOT attacks, while the measurement-free SQA protocol is vulnerable to man-in-the-middle attacks. Hence, this study reveals the severe security issues of Zhou et al.’s SQA protocol and proposes an improved protocol with guaranteed security. The proposed measure-resend SQA protocol is immune to double CNOT attacks. Since the photons sent back and forth are identical, Eve cannot obtain any information by cross-comparing these photons. In the proposed measurement-free SQA protocol, the eavesdropper cannot obtain the order of the transmitted photons because it was previously a pre-shared key to decide the order of the photons. Hence, the proposed measurement-free SQA protocol can withstand man-in-the-middle attacks.