Bots get it wrong again. "Next step is freezing who said it" It's called key-pair, and is inherent in Nostr "when" Nostr has timestamps too. Although, I'm not sure if it's easily tampered with, or can be gamed from the get-go. Another decentralized system also had this solved long ago. It's called "electronic mail". (Now for the onslaught of unfounded disdain) "and that nobody tampered with it in between" If you have the original on your own relay, the copies can be verified against it. If we're talking about tampering during transport, then employ encryption. I used Nostr to be the notary for my PMA docs. They were published to the public (i.e. not in my DMs), and I made a backup to store locally. The only "not so secure" part of my process is that I haven't run my own relay because I'm lazy.