2. Reliable client-side scanning of images is impossible (you cannot download illegal content to client devices for exact matches, so it will be only signatures and collisions are possible), so there will be false positives that will be reported, which will inevitably result in violation of privacy, possibly persecution etc.
2. You mean "Reliable classification of client-side scanned images is impossible", although you dont actually define reliable. This is besides the point, Im not talking about the actually feasibility of this on a political level, Im asserting a specific technical point that client-side scanning is 100% possible for e2e apps
The only acceptable scanning process here is the one that produces only true positives, no collateral damage. This is what I call reliable.
well then reliability is impossible, you must accept errors
Nobody should accept errors. Client-side scanning simply must not happen. It’s mathematically dumb idea.
I don't understand why someone would go through the trouble of using WhatApp to pass around separately-encrypted files instead of using anything else, though.
2. It's also "technically possible" to do the scanning server-side, on the encrypted stream, and flag anything that by chance matches a known hash.
All you need to do to avoid it would be to encrypt outside the app, something most people would not bother to do, but criminals would be motivated to do.