system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a way to know if a piece of information (document/file) was created at certain point, but not in a future time?

Besides something like carbon dating, if I create a piece of information or document, is there any mathematical or computer science way to prove that it was made, for example, on a Monday, and not on Tuesday by someone and put in Mondays date?
gpt
In order to achieve this, you need a data structure that can't be modified after the fact (except perhaps through unreasonable amounts of brute force effort).

One approach relies on a trusted authority and this approach is mimics the concept of a notarized document. You include in the document a statement on the creation date of the document authored by a trusted authority and an electronic signature for this message. The signature depends on the message in this case: Change the message and the signature has to be changed as well.

Thanks to public-key cryptography, anyone can verify that this statement was signed by whoever holds the private keys of this authority. And unless one can break the encryption scheme, there is no method to retroactively change the contents of the statement and update the electronic signature to still be valid, except by the original signing authority.

This removed the need to trust the author of the document, but replaces it with the need to trust this third party signing authority.

Another approach is to simply announce the creation of the document publicly. Post about it on a blog, take an ad out in a newspaper, etc... Having multiple public sources that date the creation means that one should be able to verify with a reasonable degree of certainty what the creation date was. However, with time, these sources become less readily available.

Finally, one could store a statement regarding the creation of the document in a blockchain structure. Blockchains such as Bitcoin allow for small messages to be embedded in transaction. By including the hash of the document in a transaction, one could create an immutable timestamp that proves the document was created no later than the timestamp of that blockchain transaction.