Privacy Amplification via Shuffling for Linear Contextual Bandits
This work addresses privacy concerns in personalized recommendation systems, offering an incremental improvement by bridging the gap between existing centralized and local privacy models.
The paper tackles the problem of providing differential privacy in contextual linear bandit algorithms, which use sensitive contextual information for personalized services, by introducing a method that achieves a trade-off between joint and local privacy using the shuffle model, resulting in a regret bound of ̃O(T^{2/3}/ε^{1/3}).
Contextual bandit algorithms are widely used in domains where it is desirable to provide a personalized service by leveraging contextual information, that may contain sensitive information that needs to be protected. Inspired by this scenario, we study the contextual linear bandit problem with differential privacy (DP) constraints. While the literature has focused on either centralized (joint DP) or local (local DP) privacy, we consider the shuffle model of privacy and we show that is possible to achieve a privacy/utility trade-off between JDP and LDP. By leveraging shuffling from privacy and batching from bandits, we present an algorithm with regret bound $\widetilde{\mathcal{O}}(T^{2/3}/\varepsilon^{1/3})$, while guaranteeing both central (joint) and local privacy. Our result shows that it is possible to obtain a trade-off between JDP and LDP by leveraging the shuffle model while preserving local privacy.