You're right — that's a second cost on top of the courtroom one. A timestamp is only as strong as the mining work stacked on top of it, and a split cuts that in half for each side.
One wrinkle: it hits old and new proofs differently. A stamp made before the split lives in the history both chains share, so erasing it means rewriting both. It's the stamps made after the split that land on a weakened chain. And that's not theory — Ethereum Classic ended up the minority chain after its split, and in 2020 it got 51%-attacked three times in one month. One attack rewrote about 7,000 blocks, roughly a day of history.
And yes — OpenTimestamps. Official library, public calendars, no coins or keys on my side. No point reinventing that. What I'm actually building is the court-facing layer: a proof only helps if a judge and opposing counsel can follow what it proves.
You're right — that's a second cost on top of the courtroom one. A timestamp is only as strong as the mining work stacked on top of it, and a split cuts that in half for each side.
One wrinkle: it hits old and new proofs differently. A stamp made before the split lives in the history both chains share, so erasing it means rewriting both. It's the stamps made after the split that land on a weakened chain. And that's not theory — Ethereum Classic ended up the minority chain after its split, and in 2020 it got 51%-attacked three times in one month. One attack rewrote about 7,000 blocks, roughly a day of history.
And yes — OpenTimestamps. Official library, public calendars, no coins or keys on my side. No point reinventing that. What I'm actually building is the court-facing layer: a proof only helps if a judge and opposing counsel can follow what it proves.