title: Renyi Differential Privacy of The Subsampled Shuffle Model In Distributed Learning
abstract: We study privacy in a distributed learning framework, where clients collaboratively build a learning model iteratively through
  interactions with a server from whom we need privacy. Motivated by stochastic optimization and the federated learning (FL) paradigm, we focus on the case where a small fraction of data samples are randomly sub-sampled in each round to participate in the learning process, which also enables privacy amplification.  To obtain even stronger local privacy guarantees, we study this in the shuffle privacy model, where each client randomizes its response using a local differentially private (LDP) mechanism and the server only receives a random permutation (shuffle) of the clients' responses without their
  association to each client. The principal result of this paper is a privacy-optimization performance trade-off for discrete randomization mechanisms in this sub-sampled shuffle privacy model. This is enabled
  through a new theoretical technique to analyze the Renyi Differential Privacy (RDP) of the sub-sampled shuffle model.  We numerically demonstrate that, for important regimes, with composition our bound
  yields significant improvement in privacy guarantee over the state-of-the-art approximate Differential Privacy (DP) guarantee (with strong composition) for sub-sampled shuffled models. We also demonstrate numerically significant improvement in privacy-learning performance operating point using real data sets. Despite these advances, an open question is to bridge the gap between lower and upper privacy bounds in our RDP analysis.
authors: Antonious M. Girgis Deepesh Data Suhas Diggavi
hIndex: Suhas Diggavi 43