When using a Broker in the PubSub model, the same shared symmetric key concepts as defined in 22.214.171.124 can be used to provide Confidentiality and Integrity. Furthermore, communication to the Broker can be secured according the rules defined for the Broker. These rules are not defined in the OPC Foundation specification but are defined by the Middleware. In many cases the Middleware requires the authorization of both the Publishers and the Subscribers before they can interact with the Broker. The Broker interactions can provide security mechanisms to meet Confidentiality, Integrity and application or user Authentication as security objectives. If the published message is not secured using the shared symmetric key concepts, the message content is visible to the Broker which creates some risk of man-in-the-middle attacks. The use of the shared symmetric keys eliminates this risk.