そうそう!! OpenPGPの電子署名のサイズは署名対象のサイズとは無関係っぽい(鍵とかハッシュとかのアルゴリズムには依存しそう)のでQRコードにできるかもわね
ちっちゃいデータの場合
$ echo Hello, World! | gpg --detach-sign --armor
-----BEGIN PGP SIGNATURE-----
iQGzBAABCgAdFiEE9glg2AsiQ4LKjYMctWwgMW1ugnkFAmEYe5wACgkQtWwgMW1u
gnl1kQv/SzlrYmJd7XVMm9w2o655IqNINqUNesjRYEbuBZIH9/RHqmWuZA6hziqM
YugXxcwgcmt1gMJ7pQaD9yh0jhvyQY0pi10iW5LZHW47fYH44h+opWAatF9e9UPL
R6xlne7oyEOT4ujQfV96205QdBJJB0Wa4xbrE9cnspoI77fhSVvMFmg75yQpfKai
8dAQP2MVTmjwiMx8JcoQDkmZCz8NFKL7pQOUCJgMHoKTdcISyX34Du4BeSq6I4QB
YJ+IvsBUePxljQoZTISI+TT7in1QzzGZFz6+F+HN0hIkmrB6MJYnkmLtE6DjjmnQ
GvqJFvUAO0OO5tSxdNUbCuH2UeWBlajdHaJA18bEtNfgI20k641xJ1ll+EUcxF7m
7v1Td010c2FkRLW2AiA61RmCp8xh2g3WzfIUYgymuUHovhy5vgO5VptFFamdQgpS
CzrFHQ0e9p6IF9Al/tscFB+q6ZAq8Osjskjjv05WoF5lrQ8F3Tfae8GFTpik//Jt
jPC4yKPx
=RJIp
-----END PGP SIGNATURE-----
おっきいデータの場合
$ ls -l ./public/sounds/boop.ogg
-rw-rw-r-- 1 zunda zunda 5247 May 18 10:42 ./public/sounds/boop.ogg
$ cat ./public/sounds/boop.ogg | gpg --detach-sign --armor
-----BEGIN PGP SIGNATURE-----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=XiL/
-----END PGP SIGNATURE-----
