Cloud services generally already do this, for example, here is Google's report:

https://transparencyreport.google.com/child-sexual-abuse-mat...

Yeh I was talking in hyperbole, but the possible attack vectors this system enables are so powerful I felt it warranted. Under this system you are able to artificially ddos organizations that verify if CP is sent by sending legitimate, low-res porn whose hash has been modified. You can trigger legitimate investigations by sending CSAM through WhatsApp or through social engineering. You can also fuck with Apple by sending obvious spam.

* With regard to the legislative branch, they can even mandate changes to this system they aren't allowed to disclose. Once this system is in place, what is stopping governments from forcing other sets of hashes for matching.

And this is just one step away from Apple and Microsoft building this scanning into the OS itself (into the kernel/filesystem code, why not?!). This is beyond insane. Stallman was right. Our devices aren't ours anymore.

Now, to be fair, there would be a secondary private hash algorithm running on Apple's servers to minimize the impact of hash collisions, but what's important is that once a file matches a hash locally, the file isn't yours anymore -- it will be uploaded unencrypted to Apple's servers and examined. How easy would it be to shift focus from CSAM into piracy to "protect intellectual property"? Or some other matter?

Jup. As others have pointed out, if Apple were willing to lie about the extent of this system and its inception date, why should we suddenly trust that they won't extend its functionality. They themselves explicitly state that the program will be extended, so if this is the starting point I don't think I will be around for the ride.

It's a shame as I really love some of their privacy-minded features (e.g. precision of access to the phone's sensors and/or media).

> Even worse, how long will it take until other cloud storage services such as Dropbox, Amazon S3, Google Drive et al implement the same features? Or worse, required by law to do so

They already do this. Google and Facebook have even issued reports detailing their various success rates…