Actually, It looks like it’s a public protocol:
https://datatracker.ietf.org/doc/draft-ietf-ppm-dap/

This paper describes it in more details. It’s using zero knowledge proofs to reject invalid vectors without seeing them:
https://arxiv.org/abs/2307.15017

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tech

Do you trust Apple's differential privacy?

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Differential privacy is pretty old and as far as I know nobody really broke it, so if they didn’t put any backdoors in it, this looks legit.

They should open source all the code. And maybe use this to fix the damn keyboard:-)