Sampled traffic analysis by internet-exchange-level adversaries

Abstract

Existing low-latency anonymity networks are vulnerable to traffic analysis, so location diversity of nodes is essential to defend against attacks. Previous work has shown that simply ensuring geographical diversity of nodes does not resist, and in some cases exacerbates, the risk of traffic analysis by ISPs. Ensuring high autonomous-system (AS) diversity can resist this weakness. However, ISPs commonly connect to many other ISPs in a single location, known as an Internet eXchange (IX). This paper shows that IXes are a single point where traffic analysis can be performed. We examine to what extent this is true, through a case study of Tor nodes in the UK. Also, some IXes sample packets flowing through them for performance analysis reasons, and this data could be exploited to de-anonymize traffic. We then develop and evaluate Bayesian traffic analysis techniques capable of processing this sampled data.