Printing your secret keys or revocation certificates on paper is a good idea to achieve long-term storage. This can be done by printing the ASCII version or by using paperkey.
Recovery is another problem and can be difficult when using raw text files. The use of QR codes is particularly effective in dealing with this issue.
The tools has been developed and tested on debian 9 only. Some packages are needed:
% apt install coreutils gawk gnupg imagemagick paperkey qrencode zbar-tools
The gpg2qr tool generate a ready to print document using QR codes. It can
handle both secret keys and revocation certificates.
% gpg2qr -i secret.(asc|gpg) -o secret.(pdf|png|...)
The qr2gpg tool read documents generated by gpg2qr and reconstruct the
secret data. It is also able to handle both secret keys and revocation
certificates. Note that, when using secret keys, the associated public key
have to be given.
% qr2gpg -i secret.(pdf|png|...) -o secret.gpg [ -p public.(asc|gpg) ]
Both tools are able to read and write from standard input / output and can be used in piped commands.
% gpg --export-secret-key <key id> | gpg2qr | lpr
% scanimage | qr2gpg [ -p public.(asc|gpg) ] | gpg --import
The gpg2qr tool suites has been inspired by the @stueja comment on the
gpg2qrcodes.sh Gist posted by @joostrijneveld.
The gpg2qr tool suites are released under the MIT License.