I was looking through Google's encryption flow and noticed that they split each file into chunks and then encrypt each chunk individually with AES-GCM with its own key.
Since AES-GCM starts to get vulnerable around $2^{48}$ messages (though, some people suggest $2^{36}$), how can they keep things secure if they have millions of users uploading files constantly?
I'm new to cryptography, so excuse my ignorance. Does the $2^{48}$ limit only actually matter on a per user basis or is it in general? I wanted to do try something similar using AES-CBC with a SecureRandom IV and HMAC for per chunk encryption since you don't have to worry about the collision. However, seeing their encryption flow, I wanted to learn more about what is the proper way of going about things.