Lightweight Authentication of Web Data via Garble-Then-Prove

Transport Layer Security (TLS) establishes an authenticated and confidential channel to deliver data for almost all Internet applications. A recent work (Zhang et al., CCS'20) proposed a protocol to prove the TLS payload to a third party, without any modification of TLS servers, while ensuring the privacy and originality of the data in the presence of malicious adversaries. However, it required maliciously secure Two-Party Computation (2PC) for generic circuits, leading to significant computational and communication overhead. This paper proposes the garble-then-prove technique to achieve the same security requirement without using any heavy mechanism like generic malicious 2PC. Our end-to-end implementation shows 14× improvement in communication and an order of magnitude improvement in computation over the state-of-the-art protocol. We also show worldwide performance when using our protocol to authenticate payload data from Coinbase and Twitter APIs. Finally, we propose an efficient gadget to privately convert the above authenticated TLS payload to additively homomorphic commitments so that the properties of the payload can be proven efficiently using zkSNARKs.