Use OpenPGP keys & standard?
Building cryptocam-cli is nontrivial (cryptocam-companion-cli#6) and resource hungry.
Gnupg is widely available and seems to provide everything needed. A little shell script calling gnupg and qrencode could make it real easy.
Also, use of OpenPGP would in principle make it possible to get the public key(s) from a public key server or encrypt to multiple recipients.