Kavli Affiliate: Xiang Zhang
| First 5 Authors: Xiang Zhang, Zhou Li, Kai Wan, Hua Sun, Mingyue Ji
| Summary:
Secure aggregation is motivated by federated learning (FL) where a cloud
server aims to compute an averaged model (i.e., weights of deep neural
networks) of the locally-trained models of numerous clients, while adhering to
data security requirements. Hierarchical secure aggregation (HSA) extends this
concept to a three-layer network, where clustered users communicate with the
server through an intermediate layer of relays. In HSA, beyond conventional
server security, relay security is also enforced to ensure that the relays
remain oblivious to the users’ inputs (an abstraction of the local models in
FL). Existing study on HSA assumes that each user is associated with only one
relay, limiting opportunities for coding across inter-cluster users to achieve
efficient communication and key generation. In this paper, we consider HSA with
a cyclic association pattern where each user is connected to $B$ consecutive
relays in a wrap-around manner. We propose an efficient aggregation scheme
which includes a message design for the inputs inspired by gradient coding-a
well-known technique for efficient communication in distributed computing-along
with a highly nontrivial security key design. We also derive novel converse
bounds on the minimum achievable communication and key rates using
information-theoretic arguments.
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