Comment by chikere232

The nearest neighbour search is sharded, which apple's blog admits is a privacy issue, which is why they're running the DP and OHTTP parts.

If apple were to add additional clusters that match "sensitive" content and endeavour to put them in their own shards distinct from landmarks, they defeat the homomorphic encryption part while still technically doing it.

The DP part can be defeated with just statistics over time; someone with any volume of sensitive content will hit these sensitive clusters with a higher likelihood than someone generateing noise injected fake searches.

The OHTTP part can be defeated in several ways, the simplest of which is just having a clause in a non-public contract allowing apple to request logs for some purpose. They're paying them and they can make up the rules as they go.