Client-side scanning (CSS, not to be confused with Cascading Style Sheets) involves analysing data on a mobile device or personal computer prior to the application of encryption for secure network transit or remote storage. CSS in theory provides a way to look for unlawful content while also allowing data to be protected off-device.
Apple in August proposed a CSS system by which it would analyse photos destined for iCloud backup on customers' devices to look for child sexual abuse material (CSAM), only to backtrack in the face of objections from the security community and many advocacy organizations.
The paper, "Bugs in our Pockets: The Risks of Client-Side Scanning," elaborates on the concerns raised immediately following Apple's CSAM scanning announcement with an extensive analysis of the technology.
"In this report, we argue that CSS neither guarantees efficacious crime prevention nor prevents surveillance," the paper says.
See
Client-side content scanning as an unworkable, insecure disaster for democracy#
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security #
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clientsidescanning #
apple 
Hopefully we're still listening to experts
