DIGITALSIGN — Digital signature

Signs a drawing with an integrity stamp and validates it.

• Command: DIGITALSIGN · Global name: _DIGITALSIGN
• Ribbon: Output › Export

Signs a drawing with a digital integrity signature and later checks whether the file has changed since it was signed.

Usage

1. Type FIRMADIG or click Digital signature.
2. Choose Sign or Validate.

Sign or validate the signature? [Sign/Validate] <Validate>:

3. Pick the DWG or DXF file in the file dialog box (with FILEDIA set to 0, type its path).

Drawing to sign or validate (DWG or DXF):

4. When signing, type the signer name (or press Enter for the system user).

Signer name (or Enter for the system user):

How it works

• Computes the file's SHA-256 and signs it with Ed25519, using the user's own key pair, created the first time and stored in <config>/lince/firma/ (the private key with restricted permissions, the public one in ed25519.pub).
• The stamp is saved next to the drawing, in <name>.lincefirma, with the signer, the date (UTC), the algorithm, the public key and the signature.
• Validating recomputes the SHA-256 and verifies the signature with the stamp's public key: valid, file changed, signed with a different key, or no signature.

Limitations

• It is a self-signed integrity signature: it proves the file has not changed and which key it came from, but not third-party trust. That needs a certificate (code signing), still pending by the user's decision.
• The signature is not embedded inside the DWG like AutoCAD's; it travels in the accompanying .lincefirma file.
• Sign the file already saved on disk: the signature is of the file bytes, not of the in-memory drawing.

See also

ETRANSMIT · QSAVE