中文摘要：

文中通过对具有无阈下信道密码系统定义的研究，指出阻止闽下信道使用的唯一方式是修改密码系统使其具有无阈下性，而且一个参与密码系统运行的主动看守是不可或缺的。在分析了Burmester—Desmedt定义缺点的基础上，基于概论图灵机模型给出了一个新的定义，最后简要讨论了具有无阈下信道密码系统的实现代价。

英文摘要：

The research on the definition of subliminal-free cryptosystems shows that the only way to prevent the use of subliminal channels is to modify the eryptosystems and to make them subliminal-free, and an active warden involved in the running of cryptosystems is indispensable. In this paper, the weakness of Burmester-Desmedt＇ s definition is analyzed, and then a new definition of subliminal-free cryptosystems based on a probabilistic Turing machine model is given. Finally, the cost of designing a complete subliminal- free cryptosystem is discussed.