GnuPG - signed Telefax communication

[Ángel]

On 2022-01-14 at 16:42 +0000, Стефан Васильев wrote:
> Hi all,
> 
> If people have a modern Telefax machine, have you ever
> tried out to send a GnuPG signed Fax?
> 
> I was thinking about the following:
> 
> One prepares his message in the following way:
> 
> ---begin message---
> 
> Message.
> 
> --end message---
> 
> Then saves the message, detach signs it and converts the
> detached signature as QR-code which is put then also on
> the Fax document, while the receiver then OCR scans the
> document and decodes the QR-code.


What's wrong with simply using a PGP clearsign signature?

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Dear Mr Васильев

I hereby send you this signed document with the information you
requested:

Gur nggnpx jvyy or ynhapurq ba fvkgu Whar

Yours faithfully
-----BEGIN PGP SIGNATURE-----

iIcEARYIAC8WIQQCizm6L17e6dtQkgGnASDnmmvMqAUCYeH06xEcYW5nZWxAMTZi
aXRzLm5ldAAKCRCnASDnmmvMqL6LAP9TIWvEqVFLAPbAZWqCegFvO2KEp/44ovJu
XpE9FoZqiQD/U4Xz0ePZJNThyxzJuNwVyh8C2Iz3Kw3DFpYf3vF68Aw=
=ZQiA
-----END PGP SIGNATURE-----



Of course, you need to properly OCR the signature, but you already need
to properly OCR all the text anyway. (Hint: the final checksum may
help). The font choice could be helpful in getting good OCR results as
well.