I’m trying to get a handle on WF 4 (which is awesome, BTW) and currently working on persistence.  We have a need to encrypt the workflow instance data, and it took me quite some time to figure out how that might best be done.  The biggest drawback to working with WF 4 right now is that the documentation is pretty lame.  There are very few samples, and beta 2 hasn’t been around long enough to generate the “this is how you solve that problem” blog posts we’ve all come to depend upon.  I looked at PersistenceParticipant, but couldn’t see a good way to make that do what I wanted, then a bunch more time trying to figure out what was going on in the SqlWorkflowInstanceStore, etc. 

I think I’ve got a workable solution, although I’ve yet to actually try it out.  Turns out that the SqlWorkflowInstanceStore keeps all that good data in varbinary(MAX) columns, and only messes with them via a set of stored procs that get created when you create the instance store schema.  It should be an easy thing to modify said stored procs to use native SQL 2005/2008 column level encryption, without having to change the schema at all. 

I’ll let you know if it works…