To decide which mechanisms we should use to protect ourselves, we need to take a first step and decide which services or functions we need. There are six main functions used to protect the distributed application from the risks I have described.

Two further services do exist the guaranteed delivery service we described earlier in the chapter on MSMQ and the error reporting services we looked at in an earlier chapter on Communication services. I will add a small note on these to show how they are relevant to the security area.

Authentication This mechanism ensures that the process or user requesting access to a system is the process/user it claims to be. Authentication is thus a test of "proof of identity," a particularly difficult service to implement in distributed applications especially if they also operate across the Internet. The principals in a transaction must be able to prove who they are, whether they are outside or inside the organization. Ideally, authorization should be bilateral the client should know who the server is and the server must know the client.

Theoretically, the user should be authenticated each time a new message is sent from that same user, but in practice once the process has been authenticated, most authentication services issue the user or process with a code or "ticket," that can be used for the duration of processing. The ticket is "attached" to the messages within the conversation so that authentication...