Symmetric key encrypt the image, upload the encrypted image with the symmetric key encrypted by your friends' pubkeys. When you add a friend just append new pu

Symmetric key encrypt the image, upload the encrypted image with the symmetric key encrypted by your friends' pubkeys. When you add a friend just append new pubkey encrypted symmetric key for each asset. Friend removal is even more expensive and requires the client side to reencrypt everything :( I'm sure there are better cryptographic constructs out there with multi key encryption that can alleviate some of the insertion and removal costs. You could do it with decent trade-offs for the content provider as well. You could obfuscate everyone else's face but yours and allow them to get access to that image and then just encrypt the map for your friends. Of course then it's all about just creating enough mock accounts to recover the full images throughout the graph. Or just take custody of a user's keys in exchange for features. Still though, it's marginally more expensive to build a mass surveillance app!