Are there any good ways to convert public keys to QR codes for easier transfer on paper or other printable media?
I have unsatisfying answers: First, if you control the receiver-side software, it’s easy. An ascii-armored “bare” GPG public key with normal metadata is comfortably under 1KB, and that will fit as a plain-text alphanumeric QR code, even with high error correction, on any of the version 30+ QR formats, and you can print that on a business card. The problems is that no “normal” software on your recipient’s side is going to do anything smart with that card.
The vCard standard allows you to specify both an e-mail address and encryption keys, so this ought to be a solution, but it doesn’t seem like a real success: see Distributing PGP Keys and Fingerprints . I can confirm that my (iOS) business card scanner app doesn’t actually and use keys provided that way.
There’s a formalized a URI scheme openpgp4fpr for GPG key fingerprints, meaning that would be a great starting place for implementing the right functionality, but, again, it doesn’t seem like anybody’s picked up the ball on that.
There’s a project here that seems relevant, but it hasn’t been touched in five years, so YMMV: GitHub - juga0/opgpcard: Create a VCard, a QR code and/or a printable business cards including OpenPGP key and fingerprint.