Identifying Website Users by TLS Traffic Analysis: New Attacks and Effective Countermeasures
A. Pironti, Pierre-Yves Strub, Karthikeyan Bhargavan · HAL (Le Centre pour la Communication Scientifique Directe) · 2012
Websites commonly use HTTPS to protect their users' private data from network-based attackers. By combining public social network profiles with TLS traffic analysis, we present a new attack that reveals the precise identities of users accessing major websites. As a countermeasure, we propose a novel length-hiding scheme that leverages standard TLS padding to enforce website-specific privacy policies. We present several implementations of this scheme, notably a patch for GnuTLS that offers a rich length-hiding API and an Apache module that uses this API to enforce an anonymity policy for sensitive user files. Our implementations are the first to fully exercise the length-hiding features of TLS and our work uncovers hidden timing assumptions in recent formal proofs of these features. Compared to previous work, we offer the first countermeasure that is standards-based, provably secure, and experimentally effective, yet pragmatic, offering websites a precise trade-off between user privacy and bandwidth efficiency.