TLShare: Private Authenticated MPC and FHE Inputs Over TLS

Transport Layer Security (TLS) allows clients to establish secure and private channels with servers. DECO (CCS'20) and follow-up works proposed protocols that enable proving the provenance of a TLS response, i.e., that a payload came from a particular server, without needing server-side modifications. Unfortunately, these works are limited to proving Boolean statements over the payload (e.g., age ≥ 18) and cannot combine payloads from multiple clients. We introduce TLShare, a framework that extracts authenticated data from a TLS connection and imports it into secure multiparty computation (MPC) or fully homomorphic encryption (FHE), without requiring server-side changes or exposing client credentials. Unlike prior work, TLShare allows the payload itself, not just a predicate about it, to serve as private input to secure downstream computation. TLShare supports combining verifiable inputs across multiple clients and servers, enabling new applications such as privacy-preserving financial risk assessment and collaborative analytics. We design three protocols for TLShare: one for MPC using verifiable secret sharing, and two for FHE using interactive and non-interactive zero-knowledge proofs, each ensuring input authenticity, integrity, and end-to-end privacy. We evaluate all three protocols of TLShare over both LAN and WAN settings, comparing their trade-offs and demonstrating their practicality.