GnuPG - signed Telefax communication

Стефан Васильев stefan.vasilev at
Fri Jan 14 21:50:57 CET 2022

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'.


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