Tzonelih Hwang

Jun Gu, Tzonelih Hwang

Recently, Tsai et al. (Laser Phys. Lett. 17, 075202, 2020) proposed a lightweight authenticated semi-quantum key distribution protocol for a quantum participant to share a secret key with a classical participant. However, this study points out that an attacker can use a modification attack to make both participants share a wrong key without being detected. To avoid this problem, an improvement is proposed here.

Jun Gu, Tzonelih Hwang

Recently, Li et al. (Int J Theor Phys: DOI: 10.1007/s10773-020-04588-w, 2020) proposed a multiparty quantum key agreement protocol via non-maximally entangled cluster states. They claimed that the proposed protocol can help all the involved participants have equal influence on the final shared key. However, this study points out a loophole that makes Li et al.'s protocol suffer from a collusion attack, i.e. several dishonest participants can conspire to manipulate the final shared key without being detected by others. To avoid this loophole, an improvement is proposed here.

Jun Gu, Tzonelih Hwang

Recently, a mutual semi-quantum key agreement protocol using Bell states is proposed by Yan et al. (Mod. Phys. Lett. A, 34, 1950294, 2019). The proposed protocol tries to help a quantum participant share a key with a classical participant who just has limited quantum capacities. Yan et al. claimed that both the participants have the same influence on the final shared key. However, this study points out that the classical participant can manipulate the final shared key by himself/herself without being detected. To solve this problem, an improved method is proposed here.

Chun-Hao Chang, Yu-Chin Lu, Tzonelih Hwang

Yu et al. and Li et al. have proposed the measure-resend protocols of authenticated semi-quantum key distribution (ASQKD). A new measure-resend ASQKD protocol is proposed in this paper, which requires a lower burden of quantum resource, needs fewer bits of the pre-shared key, and even provides better qubit efficiency than their protocols. The security proof shows the robustness of the proposed protocol under the collective attack.

Yu-Chin Lu, Chia-Wei Tsai, Tzonelih Hwang

We calculate the key sharing rate of Lu et al.'s Quantum Key Recycling (QKR) protocol. The key sharing rate is another version of the key rate, but it can be calculated for both the Quantum Key Distribution (QKD) protocols and the QKR protocols. We define the key sharing rate in this study and compare the key sharing rate of the QKR protocol to the rate of the QKD protocols. We found Lu et al.'s QKR protocol can be used to share keys more efficiently than BB84 in some situations. We also compare the six-state version of Lu et al.'s QKR protocol to the six-state QKD protocol. The results of this study show the potential advantages of using pre-shared keys to replace the public discussion in quantum protocols.

Yu-Chin Lu, Chia-Wei Tsai, Tzonelih Hwang

We propose a new Quantum Key Recycling (QKR) protocol, which can tolerate the noise in the quantum channel. Our QKR protocol recycles the used keys according to the error rate. The key recycling rate of the pre-shared keys in our QKR protocol is optimized depending on the real error rate in the quantum channel. And our QKR protocol has higher efficiency than the exiting QKR protocol with error-tolerance. The security proof shows the security of the recycled keys is universal composable.

Shih-Min Hung, Sheng-Liang Hwang, Tzonelih Hwang et al.

This study explores a new security problem existing in various state-of-the-art quantum private comparison (QPC) protocols, where a malicious third-party (TP) announces fake comparison (or intermediate) results. In this case, the participants could eventually be led to a wrong direction and the QPC will become fraudulent. In order to resolve this problem, a new level of trustworthiness for TP is defined and a new QPC protocol is proposed, where a second TP is introduced to monitor the first one. Once a TP announces a fake comparison (or intermediate) result, participants can detect the fraud immediately. Besides, due to the introduction of the second TP, the proposed protocol allows strangers to compare their secrets privately, whereas the state-of-the-art QPCs require the involved clients to know each other before running the protocol.