## Locally Differentially Private (Contextual) Bandits Learning

### Kai Zheng, Tianle Cai, Weiran Huang, Zhenguo Li, Liwei Wang

Published in NeurIPS, 2020

### Abstract

We study locally differentially private (LDP) bandits learning in this paper. First, we propose simple black-box reduction frameworks that can solve a large family of context-free bandits learning problems with LDP guarantee. Based on our frameworks, we can improve previous best results for private bandits learning with one-point feedback, such as private Bandits Convex Optimization, and obtain the first result for Bandits Convex Optimization (BCO) with multi-point feedback under LDP. LDP guarantee and black-box nature make our frameworks more attractive in real applications compared with previous specifically designed and relatively weaker differentially private (DP) context-free bandits algorithms. Further, we extend our $(\varepsilon, \delta)$-LDP algorithm to Generalized Linear Bandits, which enjoys a sub-linear regret $\tilde{O}(T^{3/4}/\varepsilon)$ and is conjectured to be nearly optimal. Note that given existing $\Omega(T)$ lower bound for DP contextual linear bandits (Shariff&Sheffe, 2018), our result shows a fundamental difference between LDP and DP contextual bandits learning.