What I want:
A single “Sign with Proton” action that works everywhere—when I’m composing in Mail, uploading to Drive, or sharing a file from any third‑party app (camera, scanner, office suite). It should use the exact private key I already have for signing Proton Mail messages, just like the Guardian Project’s ProofMode signs photos and videos.

Why it matters:
One key, all files – One cryptographic identity protects my emails, documents, spreadsheets, PDFs, photos, and videos.
Traditional document signing – The same PGP/ECC signature that lawyers and businesses trust for contracts can now be applied to any file without leaving Proton.
AI‑fake / deep‑fake defense – A valid signature (timestamp, device fingerprint, optional GPS) proves the file is exactly what I created. Any AI‑generated alteration breaks the signature, instantly flagging the content as tampered.

Security & UX details

Local signing only – Private key stays in the Secure Enclave/Keystore; only a hash of the file is signed.
Optional metadata – GPS, device ID, and a notarisation token are added only after explicit consent.
Revocation handling – Verification automatically checks Proton’s key directory for revoked keys.
Supported formats – Detached PGP signatures for any binary; embedded signatures for PDFs, Office docs, and common image/video containers (JPEG, PNG, MP4).
Batch signing – Multi‑select in Drive or the share sheet allows signing many files at once.
Benefits

Consolidates traditional document signing and modern media proof into one trusted workflow.
Gives a reliable, cryptographic way to detect AI‑generated fakes or post‑creation edits across all file types.
Strengthens Proton’s position as a unified, privacy‑first productivity suite.
Bottom line
Add a universal “Sign with Proton” feature that works in mail, Drive, and any third‑party app, leveraging the same key used for Proton Mail and inspired by Guardian Project’s ProofMode. This gives me one secure, privacy‑preserving method to certify any file and to spot AI‑generated tampering.