V-MHESA: A Verifiable Masking and Homomorphic Encryption-Combined Secure Aggregation Strategy for Privacy-Preserving Federated Learning

In federated learning, secure aggregation is essential to protect the confidentiality of local model updates, ensuring that the server can access only the aggregated result without exposing individual contributions. However, conventional secure aggregation schemes lack mechanisms that allow participating nodes to verify whether the aggregation has been performed correctly, thereby raising concerns about the integrity of the global model. To address this limitation, we propose V-MHESA (Verifiable Masking-and-Homomorphic Encryption–combined Secure Aggregation), an enhanced protocol extending our previous MHESA scheme. V-MHESA incorporates verification tokens and shared-key management to simultaneously ensure verifiability, confidentiality, and authentication. Each node generates masked updates using its own mask, the server’s secret, and a node-only shared random nonce, ensuring that only the server can compute a blinded global update while the actual global model remains accessible solely to the nodes. Verification tokens corresponding to randomly selected model parameters enable nodes to efficiently verify the correctness of the aggregated model with minimal communication overhead. Moreover, the protocol achieves inherent authentication of the server and legitimate nodes and remains robust under node dropout scenarios. The confidentiality of local updates and the unforgeability of verification tokens are analyzed under the honest-but-curious threat model, and experimental evaluations on the MNIST dataset demonstrate that V-MHESA achieves accuracy comparable to prior MHESA while introducing only negligible computational and communication overhead.