Certificate Authority, a exclusive entity in PKI frame, can sends and repeals certificate, and may organizes some confident model, for example, hierarchy model that often to use, distributed model and Web model etc.

• 认证中心CA是PKI框架中唯一能够发布和撤销证书的实体，它可以按照一定的信任模型来组织，如层次模型、分布式模型或Web模型等，在通常情况下组织成层次模型。