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.

翻译：量子密钥协商使得远程参与者能够基于各自私有输入公平地建立安全的共享密钥。在循环型多方量子密钥协商模式中，两个或更多恶意参与者可以合谋窃取诚实参与者的私有输入，或独立生成最终密钥。本文聚焦于一种强大的合谋攻击策略，其中处于特定位置的两个或更多恶意参与者能够在不暴露其恶意行为的情况下获取敏感信息或独立生成最终密钥。当前许多循环型多方量子密钥协商协议无法抵御此类合谋攻击策略。我们以近期提出的一个多方密钥协商协议为例进行安全性分析，揭示了现有循环型多方量子密钥协商协议对此类合谋攻击的脆弱性。此外，我们设计了一个通用的安全多方密钥协商模型，能够消除此类循环型密钥协商协议中的这一漏洞，并描述了实现该模型的必要步骤。所提出的模型具有通用性，不依赖于量子密钥协商的具体物理实现方式。