Sofia Celi (Brave Software), Alex Davidson (NOVA LINCS & Universidade NOVA de Lisboa), Hamed Haddadi (Imperial College London & Brave Software), Gonçalo Pestana (Hashmatter), Joe Rowell (Information Security Group, Royal Holloway, University of London)
We design DiStefano: an efficient, maliciously-secure framework for generating private commitments over TLS-encrypted web traffic, for verification by a designated third-party. DiStefano provides many improvements over previous TLS commitment systems, including: a modular protocol specific to TLS 1.3, support for arbitrary verifiable claims over encrypted data, client browsing history privacy amongst pre-approved TLS servers, and various optimisations to ensure fast online performance of the TLS 1.3 session. We build a permissive open-source implementation of DiStefano integrated into the BoringSSL cryptographic library (used by Chromium-based Internet browsers). We show that DiStefano is practical in both LAN and WAN settings for committing to facts in arbitrary TLS traffic, requiring < 1 s and ≤ 80 KiB to execute the complete online phase of the protocol.