I have seen this twice in the past week. A customer requirement is to migrate their Oracle database to a new server and they want encryption implemented.The steps defined in the request is Migrate then Encrypt. This is backwards. You should setup your encryption then migrate your data into the new server. Why is this? Well if you move your data and then put it into encrypted tablespaces you are going to be chasing ghost data.
Here is a two minute tech tip I did for Oracle Technology Network explaining the problem.