How to prove a file was not tampered?

So for one of my programming assignments, I used the turnin command as opposed to a class-specific binary that I was supposed to use. I didn't realize this until I found out that my assignment wasn't graded. To make matters worse, the assignment I turned in had been overwritten by my newer assignment.

So right now I have the source files that show timestamps that are clearly before the deadline. However, my instructor pointed out that I could easily manipulate the timestamps using the 'touch' command which is true. How else can I prove that the source files were not tampered with after the deadline? There has to be some way...

Solution 1:

Did you email those files to anyone by chance, if you can have a copy of them in Gmail, Yahoo Mail etc. then that is also a proof. As you can't fake the date time of an email having been sent from Gmail ( not unless you are a Google engineer! ).

But also this is a matter of trust, the question is does you lecturer think that you are petty enough to sink to such a level? I highly doubt the word of person over what they could have possibly have done (not unless it is in a serious trial).

Also there is something else to consider is this: If he is accusing you of not having them done before the deadline then he has to prove it, but if he is saying that they were not submitted before the due date that is something different altogether.