If only we had some way of signing messages

> Students having records of what their score was doesn't prove to the professor / university what score they received

It's better than nothing. (And good training for the real world.)

Also, most universities (and many schools now) issue academic e-mail addresses to students. In those cases, the email is definitive proof.

Emails from Canvas saying a grade is available do not currently include the actual grade in the email, so that would have to be implemented first. And it's probably not implemented quite intentionally because of FERPA.

DKIM signature could be used to verify that Canvas' server sent the email with the given content

As opposed to a screenshot of a website? Presumably the professor has a spreadsheet of all assignment grades that is submitted to the school?

Presumably the system will be back up eventually, so there's not much benefit to lying here, since at best you'll raise your grade in a few classes for a couple months, while taking on a pretty big risk of getting caught.

You forget things can be signed, with the key owned by the school. It can be done.