The X.509 trust model is only appropriate for the closed deployment model of PKI, in which the RPs and the subjects both have relationships the CAs. It is not appropriate for the open deployment model where the RP has no explicit relationship with the CA. The closed model is usually applied to contexts with limited scope such as a collaboration between organizations where each organization manages its own PKI including one or more CAs. All the relationships between all the entities (RPs, CAs and certificates holders) participating in the collaboration are clarified through agreed contracts between the involved organizations. Cross-certified CAs, bridge CAs are example of the closed model. However, in the open model, which applies to the Internet today, there is no explicit contractual relationship between the CA and the relying parties (RPs).The objective of this summary is to show the necessity of extending the X.509 trust model to include the role of technical and juridical expert.