TLS Proxies: Friend or Foe?

The use of TLS proxies to intercept encrypted traffic is controversial since the same mechanism can be used for both benevolent purposes, such as protecting against malware, and for malicious purposes, such as identity theft or warrantless government surveillance. To understand the prevalence and uses of these proxies, we build a TLS proxy measurement tool and deploy it via a Google AdWords campaign. We generate 2.9 million certificate tests and find that 1 in 250 TLS connections are proxied. The majority of these proxies appear to be benevolent, however we identify over 1,000 cases where three malware products are using this technology nefariously. We also find numerous instances of negligent and duplicitous behavior, some of which degrade security for users without their knowledge. To better understand user attitudes toward proxies, we conduct a survey of 1,261 users. The conflicting purposes of TLS proxies are also demonstrated in these findings, with users simultaneously comfortable with benevolent proxies but wary of attackers and government intrusion. Distinguishing these types of practices is challenging in practice, indicating a need for transparency and user opt-in. 1