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Recently, a (t, n) threshold group signature scheme is present in Qin et al. (Quantum Inf Process 19(2):71, 2020). In this paper, we point out that it is not a threshold signature scheme, namely any number of members can generate a valid signature. By introducing a secret sharing scheme, we show how to improve the original scheme to a threshold signature scheme. In the original scheme, the key for the one-time pad encryption is used more than once, which makes the verifier recover the key and fabricate any signature at his will. We show how to close this security loophole. And we also show how to add a round for checking the honesty of the arbitrator, and thus the trust put on the arbitrator can be reduced. [ABSTRACT FROM AUTHOR]

Ma et al. [Int. J. Theor. Phys. (2021): 1328–1338] proposed a multi-party quantum key distribution (MQKD) protocol using Bell states, in which multiple participants can distribute a group key efficiently. However, this study indicates that Ma et al.'s protocol has two security loopholes. First, an attacker can obtain the pre-shared key Ks using an eavesdropping attack. Second, the attacker uses an intercept-and-resend attack to steal the group key shared among the participants without being detected. An improved MQKD protocol is proposed to overcome these loopholes. [ABSTRACT FROM AUTHOR]

Recently, Jiang proposed a semi-quantum private comparison (SQPC) protocol without the use of a quantum measurement device (Quantum Inf Process 19:182, 2020). However, this paper highlights a security loophole during the transmission phase of the protocol in which a malicious participant can perform a double CNOT attack to steal partial information of the other participant's private secret without being detected. With the same assumption of the semi-quantum environment as Jiang's protocol, this paper presents an improved protocol by adopting a strategy of pre-sharing session keys to overcome the double CNOT attack. Moreover, a security analysis of the collective attack is also provided for Jiang's and the improved SQPC protocols. [ABSTRACT FROM AUTHOR]

Recently, Patro et al. proposed a multiple gray-scale image encryption scheme based on cross-coupled chaotic maps. The authors claimed the scheme could withstand known plain-text attacks and chosen-plaintext attacks. In this paper, we have thoroughly analysed the Patro et al. algorithm and reported the crucial loopholes. Patro et al. algorithm uses a row-wise and column-wise scrambling operation based on a secret sequence followed by a feed-forward XOR operation generating the cipher image. Exploiting the loopholes of feed-forward XOR operation and high correlation of pixels in standard images, a cryptanalysis algorithm is developed that deciphers the ciphered images generated by Patro et al. algorithm based on cipher-text only attack. Without using the secret keys, the proposed cryptanalysis algorithm successfully deciphers the cipher image and reveals the secret images. [ABSTRACT FROM AUTHOR]

As we know, it does not allow that a secure quantum communication protocol has the information leakage problem. Unfortunately, we find that there is the information leakage problem in the two quantum dialogue (QD) protocols which are respectively based on entanglement swapping between two logical Bell states under the collective-dephasing noise and the collective-rotation noise. To mend this loophole, they are masterly improved. It is proven that the improved QD protocols are without information leakage problem. Incidentally, they have some other obvious advantages compared to the previous ones. [ABSTRACT FROM AUTHOR]

Recently, He proposed a novel quantum private comparison protocol without a third party (G. P. He, Int. J. Quantum Inf. 15(2) (2016) 1750014). This paper points out that two security loopholes in He's protocol are existent. And a new QPC protocol which can avoid these loopholes is proposed without the help of a third party in this paper. [ABSTRACT FROM AUTHOR]

Recently, two novel quantum proxy blind signature schemes are proposed by Zeng et al. and Yang et al., respectively. Their schemes have made a great contribution to the development of quantum proxy blind signature (QPBS). However, we find that there exist some security loopholes which have been neglected by them, i.e., the receiver can forge the signature in Zeng et al.'s scheme and the unreasonable assumption about arbitrator exists in Yang et al.'s scheme, etc. In order to overcome these problems, some improved ideas are proposed. Moreover, we give the further discussions of QPBS in this paper. Finally, we summarize some reasonable assumptions in order to satisfy the security properties of QPBS. [ABSTRACT FROM AUTHOR]

Recently, Chaudhry et al and Kumari et al proposed an advanced mutual authentication protocol for Session Initiation Protocol on the basis of the protocol of Lu et al. The authors claimed that their schemes can be resistant to various attacks. Unfortunately, we observe some important flaws in their respective schemes. We point out that their schemes are prone to off-line password guessing and privileged insider attacks. To remedy their protocols's drawbacks, in this paper, we present a new improved authentication scheme keeping apart the threats encountered in the design of the schemes of Chaudhry et al and Kumari et al. Furthermore, the security analysis illustrates that our proposed scheme not only removes these drawbacks in their schemes but also can resist all known attacks and provide session key security. We give a heuristic security analysis and also provide the security analysis of the proposed scheme with the help of widespread Burrows-Abadi-Needham Logic. Finally, our scheme is compared with the previously proposed schemes on security and performance. [ABSTRACT FROM AUTHOR]

In the paper [ Mod. Phys. Lett. B 31 (2017) 1750150], Yin et al. proposed a semi-quantum secret sharing scheme by using Bell states. We find that the proposed scheme cannot finish the quantum secret sharing task. In addition, we also find that the proposed scheme has a security loophole, that is, it will not be detected that the dishonest participant, Charlie attacks on the quantum channel. [ABSTRACT FROM AUTHOR]

User identification plays an important role for access control in networks. Recently, Hsu and Chuang proposed a user identification scheme for distributed computer networks, which can also provide key agreement and user anonymity. However, Tsai pointed out the weakness of Hsu-Chuang's scheme and proposed an improved scheme. In this paper, we present two attacks to examine that some user identification schemes have a serious security loophole. Finally, we propose a new user identification scheme, which is more secure than the existing schemes. [ABSTRACT FROM AUTHOR]

In the literature He et al. (Quantum Inf Process, ) performed the cryptanalysis about the protocol of secure quantum auction with post-confirmation, and proposed the melioration algorithm in order to defeat the collusion among some malicious bidders in Zhao et al.'s protocol (Zhao et al. in Opt Commun 283:3194, ). But unfortunately, this protocol can't defeat the collusion among some malicious bidders either. In this paper, we will analyze the security of He et al.'s protocol and point out the potential loophole. Furthermore, we propose an improved protocol which can defeat the collusion among malicious bidders effectively. [ABSTRACT FROM AUTHOR]

Security of a quantum secret sharing of quantum state protocol proposed by Guo et al. [Chin. Phys. Lett. 25 (2008) 16] is reexamined. It is shown that an eavesdropper can obtain some of the transmitted secret information by monitoring the classical channel or the entire secret by intercepting the quantum states, and moreover, the eavesdropper can even maliciously replace the secret message with an arbitrary message without being detected. Finally, the deep reasons why an eavesdropper can attack this protocol are discussed and the modified protocol is presented to amend the security loopholes. [ABSTRACT FROM AUTHOR]

Recently, Du and Bao proposed a quantum secret sharing protocol based on two-particle transform of Bell states. We study the security of the proposed protocol and find that it is not secure, that is, the two dishonest agents, Bob and Zach, can collude to obtain Alice's secret messages without the help of the other agents. Finally, we give a possible improvement of the proposed protocol. [ABSTRACT FROM AUTHOR]

The controlled quantum dialogue protocol which was put forward recently (Kao and Hwang in Quantum Inf Process 16(5):139, 2017) is analyzed. It shows that a dishonest controller can successfully eavesdrop on the secret messages that the two users send by the different initial state attack or he (she) can disturb communication without being detected by the denial-of-service attack. To improve these security loopholes, a new method to check eavesdropping is given. The correctness and efficiency of this method is proven. [ABSTRACT FROM AUTHOR]