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The laws of quantum mechanics allow for the distribution of a secret random key between two parties. Here we analyse the security of a protocol for establishing a common secret key between N parties (i.e. a conference key), using resource states with genuine N-partite entanglement. We compare this protocol to conference key distribution via bipartite entanglement, regarding the required resources, achievable secret key rates and threshold qubit error rates. Furthermore we discuss quantum networks with bottlenecks for which our multipartite entanglement-based protocol can benefit from network coding, while the bipartite protocol cannot. It is shown how this advantage leads to a higher secret key rate.

The intense research activity on Twin-Field (TF) quantum key distribution (QKD) is motivated by the fact that two users can establish a secret key by relying on single-photon interference in an untrusted node. Thanks to this feature, variants of the protocol have been proven to beat the point-to-point private capacity of a lossy quantum channel. Here we generalize the main idea of the TF-QKD protocol introduced by Curty et al to the multipartite scenario, by devising a conference key agreement (CKA) where the users simultaneously distill a secret conference key through single-photon interference. The new CKA is better suited to high-loss scenarios than previous multipartite QKD schemes and it employs for the first time a W-class state as its entanglement resource. We prove the protocol's security in the finite-key regime and under general attacks. We also compare its performance with the iterative use of bipartite QKD protocols and show that our truly multipartite scheme can be advantageous, depending on the loss and on the state preparation.

Secure communication is one of the key applications of quantum networks. In recent years, following the demands for identity protection in classical communication protocols, the need for anonymity has also emerged for quantum networks. Here, we demonstrate that quantum physics allows parties—besides communicating securely over a network—to also keep their identities secret. We implement such an anonymous quantum conference key agreement by sharing multipartite entangled states in a quantum network. We demonstrate the protocol with four parties and establish keys in subsets of the network—different combinations of two and three parties—whilst keeping the participating parties anonymous. We additionally show that the protocol is verifiable and run multiple key generation and verification routines. Our work thus addresses one of the key challenges of networked communication: keeping the identities of the communicating parties private.

Quantum conference key agreement (CKA) enables key sharing among multiple trusted users with information-theoretic security. Currently, the key rates of most quantum CKA protocols suffer from the limit of the total efficiency among quantum channels. Inspired by the coherent one-way and twin-field quantum key distribution (QKD) protocols, we propose a quantum CKA protocol of three users. Exploiting coherent states with intensity 0 and μ to encode logic bits, our protocol can break the limit. Additionally, the requirements of phase randomization and multiple intensity modulation are removed in our protocol, making its experimental demonstration simple.

Confidentiality of maintaining the Electronic Health Records of patients is a major concern to both the patient and Doctor. Sharing the data on cloud is one of the most efficient technology infrastructures with extensive potential application, but at the same time there is a threat of hacking the data. Here we implement the concept for sharing of electronic health record on cloud that permits multiple members of the group to easily share the group data. With the increase in size of healthcare data the time and space complexity increases. The main challenge here is data security. This research article emphasis on a secured method for sharing the data on cloud and generation of the key that is safe from unauthorized user. In this Research article, we implement the soft computing approach for key agreement protocol using Block based design to support several users that can adapt it-self to upsurge the number of users in the cloud which depends on the assembly of the block design. This protocol generates a common conference key for all members. On comparing our results with some prevailing techniques, we accomplish that the results of our research have a better computational complexity.

Quantum conference key agreement is an important cryptographic primitive for future quantum network. Realizing this primitive requires high-brightness and robust multiphoton entanglement sources, which is challenging in experiment and unpractical in application because of limited transmission distance caused by channel loss. Here we report a measurement-device-independent quantum conference key agreement protocol with enhanced transmission efficiency over lossy channel. With spatial multiplexing nature and adaptive operation, our protocol can break key rate bounds on quantum communication over quantum network without quantum memory. Compared with previous work, our protocol shows superiority in key rate and transmission distance within the state-of-the-art technology. Furthermore, we analyse the security of our protocol in the composable framework and evaluate its performance in the finite-size regime to show practicality. Based on our results, we anticipate that our protocol will play an important role in constructing multipartite quantum network. Realizing quantum conference key agreement is challenging in experiment and unpractical in application because of limited transmission distance caused by channel loss. The authors present here a quantum conference key agreement protocol with spatial multiplexing nature and adaptive operation, which can break limitations on quantum communication over network and thus shed some light on future global quantum network.

Abstract Quantum entanglement plays a pivotal role in many communication protocols, like secret sharing and quantum cryptography. We consider a scenario where more than two parties are involved in a protocol and share a multipartite entangled state. In particular, we considered the protocol of Controlled Quantum Key Distribution (CoQKD), introduced in the reference H. Chao, X. Peng, and G. G-Can, Chin. Phys. Lett. 20, 183 (2003), where, two parties, Alice and Bob establish a key with the cooperation of other parties. Other parties control/supervise whether Alice and Bob can establish the key, its security and key rate. We discuss the case of three parties in detail and find suitable resource states. We discuss the controlling power of the third party, Charlie. We also examine the usefulness of the new resource states for generating conference key and for cooperative teleportation. We find that recently introduced Bell inequalities can be useful to establish the security of the conference key. We also generalize the scenario to more than three parties. Graphical abstract

Multipartite entanglement enables secure group key distribution among multiple users while providing immunity against hacking attacks targeting source devices, thereby realizing source-independent quantum conference key agreement (SI-QCKA). However, previous experimental demonstrations of SI-QCKA have encountered substantial technical challenges, primarily due to the low efficiency and scalability limitations inherent in the generation and distribution of multipartite entanglement. Here, we experimentally demonstrate a scalable and efficient SI-QCKA protocol using polarization-entangled photon pairs in a three-user star network, where Greenberger-Horne-Zeilinger correlations are realized via a post-matching method. We achieve a secure group key rate of \\(2.11 10^4\\) bits/s under the single-user channel transmission of 1.64 \\(\\) \\(10^-1\\) in a symmetric channel loss network. Additionally, we conduct six sets of experiments to investigate the impact of varying channel transmission and random basis selection probabilities on secure key rates. Our work establishes an efficient pathway for SI-QCKA and demonstrates potential scalability for future large-scale multi-user quantum networks.

Quantum Conference Key Agreement (CKA) provides a secure method for multi-party communication. A recently developed interference-based prepare-and-measure quantum CKA possesses the advantages of measurement-device-independence, namely, being immune to side-channels from the detector side. Besides, it achieves good key rate performance, especially for high-loss channels, due to the use of single photon interference. Meanwhile, several fully passive QKD schemes have been proposed, which eliminate all side channels from the source modulation side. We extend the fully passive idea to an interference-based CKA, which has a high level of implementation security for many-user communication.

A τ -time key agreement system ( τ -time KAS) is an unconditionally secure key agreement where an attacker cannot obtain any information about the challenge conference key even if he eavesdrops executions of τ (maybe repetitive) conferences and corrupts a predefined number of users. Here, an eavesdropped conference may contain a corrupted user, who could be useful in learning personal secret keys of uncorrupted users. In the model of Blundo et al. (Comp J, 1999), an eavesdropped conference is required to be uncorrupted. We show that the former model is strictly stronger than the latter. The size of the protocol transcript is related to the efficiency of KAS. We show that if the protocol transcript of KAS has the same entropy as the conference key, then this scheme is no better than a certain key pre-distribution scheme (KPS). For a secure KAS, it is desired that the protocol transcript does not leak any information about a user’s personal secret key. We show that if this is true, then the underlying KAS is again no better than a certain KPS. For τ > 1, every previous τ -time KAS needs a global counter to maintain the number of conferences executed so far. We show that polynomially synthesizing d -independent KPS gives a d -time KAS without a global counter.