可证明的优化公平交换及其拓展研究

The fair exchange issue, namely how to exchange digital items in a fair way, has been considered as a long standing research problem in both electronic commerce and cryptography. Optimistic fair exchange (OFE) is a kind of protocols aimed at solving this problem with the help of a semi-trusted third party. A fundamental work of OFE is to define security models capturing realistic attacks and design schemes secure in those models. The chosen-key model, proposed by Huang et al. in 2008, was considered as the most desirable model for OFE. Since 2014, the chosen-key model has been separately enhanced in three aspects. In this project, we will, for the first time, consider OFE in the enhanced chosen-key model (combining the three enhanced aspects and capturing them in a single model). We mainly focus on the following research work: (1) the general construction of OFE secure in the enhanced chosen-key model; (2) the concrete OFE constructions with high efficiency and based on weak assumptions; (3) extending the enhanced chosen-key model to the variants of OFE, investigating their securities and proposing new protocols for the variants of OFE. Our aim is to design efficient schemes for OFE and its variants that are secure in the enhanced chosen-key model with simple assumptions.

优化公平交换（OFE）是一类致力于在第三方帮助下解决电子公平交换问题的协议。OFE的一个基础工作是定义覆盖现实攻击的安全模型，然后基于所提出的安全模型设计出安全的交换协议。选择公钥模型一度被认为是最优的安全模型。近来的研究对该模型从三个不同的方面分别进行了加强。在该项目中，我们第一次在加强的选择公钥模型（三方面均加强后综合统一的模型）下研究OFE。我们主要致力于以下的研究：（1）提出在加强的选择公钥模型下安全的OFE协议的一般性构造方法；（2）构造出具体的，基于较弱的数学困难问题假设的，效率高的OFE协议；（3）把加强的选择公钥模型拓展到OFE的变种及其他应用中，评估已有协议的安全性，并为OFE的变种及其他应用构造新的协议。我们的目标为OFE及其变种与其他应用构造在选择公钥模型下安全的，基于较弱数学困难问题假设的，效率高的协议。