encrypted repositories?

Greetings,

I have a rather special usage scenario.

Assume you have a repository where you want to work on embargoed information, so that not even system administrators of the server you're pushing to can get a hold of the cleartext data.

"Server" would be a central reference repository that I can push to. "Client" would by my working computer that has a clone of the crypted repo, and an unencrypted checkout of it. Perhaps the client would also need an unencrypted copy of the repo (for performance reasons, I'm not sure about that) that gets encrypted on the fly when pushing and decrypted when fetching.

Examples of use might be press releases of upcoming products, written exams for students, whatever.

Requirements:
- "client" that is about to push must encrypt the data before pushing it  
to the server.
- all data (including file names, log messages,

Allowed restrictions:
- "server" limited to bare repositories
- initial version limited to symmetric encryption with pre-shared secret

In a later step, some key management and asymmetric crypto would be useful, but that's not crucial now. In my current scenario, those who are working on the embargoed material would trust one another.

How would one go about this from the user side? I sincerely doubt I have the resources (time!) to actually implement this in Git.

TIA