Honest-But-Curious

An honest-but-curious party follows the protocol but tries to learn extra information from messages, metadata, or outputs.

Practical Example

A federated learning coordinator aggregates updates correctly but inspects individual updates for signals about a hospital's patient population.

Good Fit

This model is useful for early designs, mutually governed collaborations, and systems where protocol deviation is unlikely.

Limits

It does not cover malformed inputs, poisoning, selective aborts, query abuse, or compromised participants.

PET Implications

MPC, PSI, HE, secure aggregation, and clean rooms often start here. Add stronger controls when incentives are not aligned.