"Billions of people worldwide use private messaging platforms like Signal, WhatsApp, and iMessage to communicate securely. This is possible thanks to end-to-end encryption (E2EE), which ensures that only the sender and the intended recipient(s) can view the contents of a message, with no access possible for any third party, not even the service provider itself. Despite the widespread adoption of E2EE apps, including by government officials, and the role of encryption in safeguarding human rights, encryption, which can be lifesaving, is under attack around the world. These attacks most often come in the form of client-side scanning (CSS), which is already being pushed in the EU, UK, U.S., and Australia.
CSS involves scanning the photos, videos, and messages on an individual’s device against a database of known objectionable material, before the content is then sent onwards via an encrypted messaging platform. Before an individual uploads a file to an encrypted messaging window, it would be converted into a digital fingerprint, or “hash,” and compared against a database of digital fingerprints of prohibited material. Such a database could be housed on a person’s device, or at the server level.
Proponents of CSS argue that it is a privacy-respecting method of checking content in the interests of online safety, but as we explain in this FAQ piece, CSS undermines the privacy and security enabled by E2EE platforms. It is at odds with the principles of necessity and proportionality, and its implementation would erode the trustworthiness of E2EE channels; the most crucial tool we have for communicating securely and privately in a digital ecosystem dominated by trigger-happy surveillance."
https://www.accessnow.org/why-client-side-scanning-is-lose-lose-proposition/
