Graph Convolutional Neural Networks (GCNs) have gained widespread popularity
in various fields like personal healthcare and financial systems, due to their
remarkable performance. Despite the growing demand for cloud-based GCN
services, privacy concerns over sensitive graph data remain significant.
Homomorphic Encryption (HE) facilitates Privacy-Preserving Machine Learning
(PPML) by allowing computations to be performed on encrypted data. However, HE
introduces substantial computational overhead, particularly for GCN operations
that require rotations and multiplications in matrix products. The sparsity of
GCNs offers significant performance potential, but their irregularity
introduces additional operations that reduce practical gains. In this paper, we
propose FicGCN, a HE-based framework specifically designed to harness the
sparse characteristics of GCNs and strike a globally optimal balance between
aggregation and combination operations. FicGCN employs a latency-aware packing
scheme, a Sparse Intra-Ciphertext Aggregation (SpIntra-CA) method to minimize
rotation overhead, and a region-based data reordering driven by local adjacency
structure. We evaluated FicGCN on several popular datasets, and the results
show that FicGCN achieved the best performance across all tested datasets, with
up to a 4.10x improvement over the latest design.