可信计算组织TCG［1］提出了一系列技术规范，但该组织没有考虑密钥的分级问题。文献［2］解决了密钥的分级问题，但同一级别用户通信时使用同一个密钥，一个级别的任一用户同另一个低级别的任一用户通信也用级别低用户（所在类）的密钥，在某些情况下，这是我们不希望的。本文给出两种方法，用这两种方法，某一级别的用户能主动与同级别的用户或级别低的用户进行保密通信，且用的密钥是不同的，而不能主动与级别高的用户进行保密通信。

TCG（trusted computing group） develops a series of technical specifications［1］，but it does not deal with the problem of hierarchical key assignment. This problem has been solved in reference ［2］.But in ［2］,the users of the same level use the same key and any user of the higher level uses the key of the user(of the lower level) in secure communications,which is undesirable in some cases. In this paper，we give two methods，by which the users can securely communicate with the users of the same level or the users of the lower level using different keys,and can not securely communicate with the users of the higher level.