I am trying to achieve the following:
Encrypted files are stored on users filesystem. The user uses my client to authenticate against a server. Once he is authenticated successfully he gets a token to decrypt the files.
things i want to ensure: the user should not be able to cache the token for later use. like a one time token, so that he is no longer able to decrypt the files in some time in the future.
the client and server do only exist in my head, so anything that is possible can be applied to it.
so, i am looking for algorithms/protocols to achieve my requirement. Any ideas on that?