This paper presents a model of hierarchical organization of Certification Authorities which can be applied to any open system network. In order to study the feasibility of the proposed model, a pilot experiment within a university environment is being carried out. The authors of this paper have developed an application which provides the users with security services using X.509 certificates. The authors have also developed a security server to provide RSA keys and management of certificates. The hierarchical infrastructure that is being created needs a multi-level policy which implies the use of various types of documents which are managed by people with different roles. One of the objectives being followed is to formalize the treatment of the information about policy, for which some components of the extensions field of the version 3 certificate have been used and other new ones are proposed.