Secure multiparty quantum key agreement against collusive attacks

Quantum key agreement enables remote participants to fairly establish a secure shared key based on their private inputs. In the circular-type multiparty quantum key agreement mode, two or more malicious participants can collude together to steal private inputs of honest participants or to generate the final key alone. In this work, we focus on a powerful collusive attack strategy in which two or more malicious participants in particular positions, can learn sensitive information or generate the final key alone without revealing their malicious behaviour. Many of the current circular-type multiparty quantum key agreement protocols are not secure against this collusive attack strategy. As an example, we analyze the security of a recently proposed multiparty key agreement protocol to show the vulnerability of existing circular-type multiparty quantum key agreement protocols against this collusive attack. Moreover, we design a general secure multiparty key agreement model that would remove this vulnerability from such circular-type key agreement protocols and describe the necessary steps to implement this model. The proposed model is general and does not depend on the specific physical implementation of the quantum key agreement.

Novel multi-party quantum key agreement protocols under collective noise

Based on the logic Bell states, we present two novel multi-party quantum key agreement (QKA) protocols under collective noise. The proposed protocols make full use of four-qubit logic Bell states as quantum resources and perform the novel encoding operation to generate the shared key. The security analysis shows that these two protocols can resist against both participant and outsider attacks. Furthermore, compared with the other existing multi-party QKA protocols over collective noise, our protocols have higher qubit efficiency. Finally, we perform the simulation of the relationship between efficiency and security, which is completely consistent with the conclusion of the security analysis of the protocols.