I have a WCF client/service app that relies on secure communication between two machines and I want to use use x509 certificates installed in the certificate store to identify t
Check out the WCF Security Guidance page on Codeplex - excellent and very useful stuff!
In particular, check out the How-To's and even more specifically the
How To – Use Certificate Authentication and Message Security in WCF calling from Windows Forms
It explains in great detail how to set up a WCF service which requires its clients to present a valid certificate, and how to check that. If you want to allow only a single client, deploy that certificate only specifically to that one single client.
Hope this helps!