Related to "How to know whether a textfile has been edited or tampered with?", I wonder if it's possible to detect file tampering on the local system?
Typical threat model: the old "Hack" computer game. I want to write out saved game state and later, when the user continues their saved game, I want to confirm they haven't edited the saved game file.
We can assume that the user has access to both the saved game file and the game executable.
Can this be done entirely on the local system, without resorting to storing hashes or signatures on a secure remote system?
I fear that the answer is "it's not possible", since any hash seed or signature key I apply to the saved game can be extracted from the executable.