Help Proofs of prior existence - Volfieldd/deux-regards GitHub Wiki
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For each imported photo, the site builds by itself a proof that you held this file on a given date, verifiable without the site.
How it is done
- Fingerprint: at import, the site computes the SHA-256 fingerprint of the original, a kind of “DNA” of the file. A single changed pixel gives a different fingerprint.
- Timestamp: this fingerprint alone, never the photo, is sent to a timestamping authority, which returns a signed token attesting the date.
- Check: the site verifies the token (signature, authority, date), then keeps it.
If it fails (network, service unavailable), the site retries by itself: a few minutes later, then every hour.
On a photo's details
| Item | Meaning |
|---|---|
| SHA-256 fingerprint | the “DNA” of the original |
| Timestamped on … UTC | the guaranteed date (universal time: +1 h in winter, +2 h in summer for Paris) |
| Authority, no. | who signed the token, and its number |
| Pending | request not yet completed: Retry now button |
Buttons:
- Original: the exact file whose fingerprint was timestamped.
- Token (.tsr): the signed token.
- Proof sheet: a readable summary, with the verification commands.
- Authority certificate: to verify the signature.
- Verify the proof: runs all the checks again.
- “Valid proof”: the original is intact, and the signature is verified up to the authority.
- “Invalid proof: the original has been modified”: the file on the server is no longer the one that was timestamped. Restore it from a backup.
- “Valid signature… but authority not verified”: the server does not have the authority's root certificate. Let the person who administers it know.
In case of dispute
Download the four files and keep them together, outside the site. Anyone can then verify the proof with OpenSSL; the commands are in the proof sheet. Add your RAW files and the neighbouring frames from the same session: the site's proof establishes the date, the RAW establishes the author.
Before deleting a photo, download its proof: it is deleted along with the photo.