The use of a warrant and the use of encryption should be completely orthogonal. It has nothing to do with "privilege" of electronic information. It's simply about the format in which information is stored.
Except that using encryption can directly affect the ability to execute the warrant, similarly to how you would use a shredder on physical documents.
The files are in a state which is extremely difficult to work with, for the express purpose of preventing their access even with a warrant. Is that obstruction of justice? It would be with a shredder or a safe wired to burn papers if forced open.
