I found the problem statement and every reply remarkably confusing, because I am not smart. I'd like to give an answer to help fellow not-smart people.
The goal is to prove that you did something in the past -- for example, that you proved a theorem, or that you predicted that COVID would become an issue way back in 2018.
Interestingly, patio11 solved this for COVID: He published a hash of his article, calling out COVID in Japan, to Twitter, which has no edit button. Then a month or so later, he published the article itself, proving that he did in fact write that article a month prior.
It's an old solution, not his. But that's the general idea here.
I think what OP meant when speaking about sides was this:
If I show you a video today, where in the video I am holding the newspaper from 1 year ago, then (excluding any video manipulation) you can be reasonably sure that I did not record the video prior to 1 year ago because prior to that the newspaper for that day did not yet exist. So I have given reasonable proof for one direction in time; that it can’t have been further back in time than that.
But the other direction in time, and what I think they are referring to as “the other side”, is forward.
With the same video, you decide to trust that it wasn’t filmed prior, but it could have been filmed at any point in time since.
So what OP is asking for is for a way to prove that a message (text, video, or whatever else) was composed no later than some point t2 in time.
And for this the suggestions in this thread are good.
And if you combine techniques then you can to some extent prove that a message was composed between two specific points in time.
For example, by having the message reference a fact that was not known prior to point t1 in time and then having the message itself or a hash of the message notarized at point t2 in time in a medium that can be reasonably trusted.
But still it is challenging, with things like the possibility that you created and notarized separate messages for all possible outcomes for example and chose to divulge only the notarization of the outcome that actually happened after the outcome was known.
You have articulated my original question perfectly. I was having a difficult time explaining it.
Interesting that so many people have posted ideas regarding block chains and hashing, which is to be expected from a programmer's forum I suppose.
My eventual solution all be it not perfect is to record my message on a clear night with the ISS passing over. I believe this could be faked but would be quite difficult to align my geo position, the moon phase and relative position of planets, stars and space station all inside a moving video.
“In the XVII century, as at the present time, the question of scientific priority was of great importance to scientists. However, during this period, scientific journals had just begun to appear, and the generally accepted mechanism for fixing priority by publishing information about the discovery had not yet been formed. Among the methods used by scientists were anagrams, sealed envelopes placed in a safe place, correspondence with other scientists, or a private message”
Another threat vector would be takeover of your account. Attacker might then publish counterfeit hashes, or perhaps find some way to get the account disabled and hidden from public view, depending on Twitter policy toward problematic accounts at that time.
The goal is to prove that you did something in the past -- for example, that you proved a theorem, or that you predicted that COVID would become an issue way back in 2018.
Interestingly, patio11 solved this for COVID: He published a hash of his article, calling out COVID in Japan, to Twitter, which has no edit button. Then a month or so later, he published the article itself, proving that he did in fact write that article a month prior.
It's an old solution, not his. But that's the general idea here.