A GDS, that also provides certificate management, supports User Access security as described in OPC 10000-12. This includes restricting all certificate management functionality to administrators. Furthermore, the list of Clients that are allowed to access management functionality may be limited.
Certificate management includes a provisioning phase and run time phase. The provisioning phase is when the GDS is providing initial certificate(s) to Clients or Servers that are just entering the system. The runtime phase is the day to day operation of system and includes providing updated CRLs, certificate renewals and updated trust lists.
The provisioning of systems is inherently not secure, but can be very useful in providing a greatly simplified deployment of a complex system. Provisioning in a GDS is not enabled by default, but requires an administrative action to enable. It is also recommended that the provisioning feature, when enabled, will only stay enabled for a limited time.
The runtime phase of GDS certificate operations can be performed in a very secure manner, since all Servers and Clients already have certificates to ensure a secure connection. For the push model of certificate management, the GDS establishes a secure channel using the highest security level available in the target Server. It does not provide updated CRLs, Certificates or TrustLists via an endpoint that has a lower security level than the security level of the updates. For example if a 4096 certificate is to be updated it cannot be updated using a 2048 channel, but a 2048 certificate can be updated using a 4096 channel. If a new higher level certificate needs to be deployed, it is handled in the same manner as the provisioning of a new server.