Security settings management using the SecuredApplication|OPC UA Standard|Forum|OPC Foundation

The text was not clear and has been updated for 1.05

https://apps.opcfoundation.org…..hp?id=4666

Applications shall never communicate with another application that they do not trust. An Application decides if another application is trusted by checking whether the Application Instance Certificate for the other application is trusted. A Certificate is only trusted if its chain can be validated. Applications shall rely on lists of Certificates provided by the Administrator to determine trust. There are two separate lists: a list of trusted Certificates and a list of issuer Certificates (i.e. CAs). The list of trusted Certificates may contain a Certificate issued to another Application or it may be a Certificate belonging to a CA. The list of issuer Certificates contains CA Certificates needed for chain validation that are not in the list of trusted Certificates.

When building a chain each Certificate in the chain shall be validated back to a CA with a self-signed Certificate (a.k.a. a root CA). If any validation error occurs then the trust check fails. Some validation errors are non-critical which means they can be suppressed by a user of an Application with the appropriate privileges. Suppressed validation errors are always reported via auditing (i.e. an appropriate Audit event is raised).

Determining trust requires access to all Certificates in the chain. These Certificates may be stored locally or they may be provided with the application Certificate. Processing fails with Bad_SecurityChecksFailed if an element in the chain cannot be found. A Certificate is trusted if the Certificate or at least one of the Certificates in the chain are in the list of trusted Certificates for the Application and the chain is valid.