GnuPG - signed Telefax communication

Stuart Longland stuartl at
Fri Jan 14 23:02:54 CET 2022

On Fri, 14 Jan 2022 20:50:57 +0000
Стефан Васильев <stefan.vasilev at> wrote:

> Stuart Longland wrote:
> > 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.  
> Thanks for sharing your experience, much appreciated!
> > 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.  
> Would you like to explain a bit such schemes? I am aware, for example,
> that GnuPG on a mini offline laptop can beat *all* smartphone crypto
> messenger, when it comes to endpoint security, when used with a dumb
> phone with a USB port and while sending GnuPG MMS messages. All
> users need for that is a software from GitHub, which can convert GnuPG
> messages to .png images and back. Simply search there for 'imgify'. is one such scheme, intended for
making a private key back-up.  It could probably be adapted to store
arbitrary data.

There may be others, I just can't put my finger on them now.
Stuart Longland (aka Redhatter, VK4MSL)

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

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