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Comment by deno | Hacker News Reader

Here’s a cool example of secret sharing from the paper[1]:

> App store. A mobile application platform (e.g., Apple’s App Store or Google’s Play) can run one Prio server, and the developer of a mobile app can run the second Prio server. This allows the app developer to collect aggregate user data without having to bear the risks of holding these data in the clear.

However I would like to know why Firefox doesn’t want to just adapt RAPPOR instead. It seems like a better fit for general telemetry, and it’s already used by Chromium.

I guess you can intersect and union Prio datasets in ways you can’t with RAPPOR?

[1] https://crypto.stanford.edu/prio/paper.pdf

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Google RAPPOR technique adds noise to the report at client (user) side. The noisy reports are then collected to a central server for analysis.

Doing this guarantees differential privacy, a strong privacy protection.

However, the major disadvantage of RAPPOR is that we get a collection of very noisy data points. Therefore, we need a very big collection to learn anything useful at all!

If the number of clients/users/records is small, RAPPOR is practically useless.

Prio, on the other hand, adds NO noise to client's reports. It uses crypto magic to compute some functions (mean/sum/...) on the collection of reports by a network of servers. Only outputs of these functions are known. No reports are leaked until at least one server is honest!

However, Prio has no guarantee that the computed output doesn't leak information about client's reports (in fact, it surely leaks some information). While, RAPPOR guarantees this protection statistically!

A current research direction is to add noise to the output of Prio as such it guarantees differential privacy.

RAPPOR relies on differential privacy only, including to protect the privacy of individual inputs; by necessity this limits the utility of the output. With Prio the inputs are protected cryptographically, which means you can have higher utility outputs (i.e. you can add less noise and achieve the same level of differential privacy). Combining DP and MPC techniques like Prio is an interesting research topic at the moment and comes up in a lot of "secure aggregation" settings.

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