What technique can protect a secret from a fully trusted user?

Question

I am programming a system using C#. My program generates a small message (a hash digest for a file) that I want to store on the hard disk - but I don\'t want the user to be

Answer 1

In one of the comments to another answer, you wrote:

It's an attempt to make a certain log file tamper proof.

If that's really the case, then perhaps you should take a different approach and move the log file to a place where the user is not fully trusted (ie: some other system).

Otherwise, you cannot guarantee the security of the file (as others have mentioned).