时间相关密码协议逻辑及其形式化语义

在密码协议中,主体的认知与信仰状态是随时间推移而不断变化的.为了在协议分析中体现这种动态性,提出一种时间相关密码协议逻辑.该逻辑基于谓词模态逻辑,通过在谓词及模态词中引入时间参数以体现时间因素,使得逻辑可表达各个主体在协议不同时间点的行为、知识及信仰.给出该逻辑的形式化语义,在避免逻辑语言二义性的同时保证了逻辑的可靠性.该语义基于Kripke结构,将可能世界建立在主体局部世界与时间局部世界的基础上,使得任一可能世界能够反映协议的一个可能的全过程.该逻辑为密码协议,特别是时间相关密码协议提供了灵活的分析方法,增强了基于逻辑方法的协议分析能力.In cryptographic protocols, the agent's epistemic and doxastic states are changeable over time. To model these dynamics, a time-dependent cryptographic protocol logic is proposed. Our logic is based on the predicate modal logic and the time factor can be expressed in it by invoking a time variable as a parameter of predicates and modal operators. This makes it possible to model every agent's actions, knowledges and beliefs at different time points. We also give the formal semantics of our logic to avoid the ambiguity of its language and make the logic sound. The semantics is based on the kripke structure and the possible world in it is built both on the local world of agent and the specific world of time. This makes every possible world can give a global view of each point of the protocol. Our logic provides a flexible method for analyzing the cryptographic protocols, especially the time-dependent cryptographic protocols, and increases the power of the logical method for analyzing protocols. © ISCAS

一种基于恶意主体的通用公平交换协议

在公平交换协议中,无可信第三方的协议不能实现较充分的公平性,离线可信第三方协议在恶意主体的情况下仍需第三方的介入,且效率大大降低。另外,现有的公平交换协议大多针对特定项的交换,通用性不强。针对以上不足,采用低负荷在线第三方的方法,提出了一种基于恶意主体的通用公平交换协议,并给出了可能影响协议公平性的各种属性分析。分析结果表明,该协议降低了对环境的要求,增强了交换的通用性,克服了一些现有交换协议公平性隐患,同时保持了较高的效率。In fair exchange protocols, a protocol without trusted third party (TTP) cannot support fairness fully, and an off-line TTP protocol also needs TTP and suffers low efficiency when the agents of the protocol are malicious. Moreover, most of the current fair exchange protocols aim at exchanging specific items and thus lose their universality. With the method of lowload on-line TTP to tackle the above deficiency, a generic fair exchange protocol based on malicious agents was proposed, and properties affecting the fairness were analyzed. The analysis result shows that the protocol requires less on environments, provides universality on fair exchange, avoids most fairness problems in the current protocols, and keeps high efficiency