GnuPG - signed Telefax communication

Stuart Longland stuartl at
Fri Jan 14 21:33:43 CET 2022

On Fri, 14 Jan 2022 17:54:56 +0000
Стефан Васильев via Gnupg-users <gnupg-users at> wrote:

> > If QR is an option, why not encode the entire message in QR?  
> I thought about that too, but in case the document would be several
> pages long and would not fit into a QR-code. Ok, one can split the
> large document and insert then several QR-codes into one Fax page.

I've experimented with using QR codes with OpenPGP on-and-off… mostly
as a mechanism for sharing the public keys: the idea being that you
could have business cards printed up with the back side containing a QR
code of your public key (not a fingerprint, the actual key).

In my experience, it is very hard to get the big and complex QR codes
to scan reliably.  Some of the QR codes used for COVID-19 contact
tracing and vaccination status _really_ push the limits -- with those
largish codes often failing to scan.

ECC keys could be made small enough to have a snowflake's chance in
hell of working.  4096-bit RSA was a no-go.

There are schemes for encoding an image for printing onto a piece of
paper and later scanning it back in to recover the original data.  QR
code is obviously a more recent option, but was not the first.  These
may be worth pursuing.
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...'s backed up on a tape somewhere.

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