Users around the world face escalating network interference such as censorship, throttling, and interception, largely driven by the commoditization and growing availability of Deep Packet Inspection (DPI) devices. Once reserved for a few well-resourced nation-state actors, the ability to interfere with traffic at scale is now within reach of nearly any network operator. Despite this proliferation, our understanding of DPIs and their deployments on the Internet remains limited---being network intermediary leaves DPI unresponsive to conventional host-based scanning tools, and DPI vendors actively obscuring their products further complicates measurement efforts.

In-network devices around the world monitor and tamper with connections for many reasons, including intrusion prevention, combating spam or phishing, and country-level censorship. Connection tampering seeks to block access to specific domain names or keywords, and it affects billions of users worldwide with little-to-no transparency. To detect, diagnose, and measure connection-level blocking, "active" measurement techniques originate queries with domains or keywords believed to be blocked and send them from vantage points within networks of interest. Active measurement efforts have been critical to understanding how traffic tampering occurs, but they inherently are unable to capture critical parts of the picture. For instance, knowing the set of domains in a block-list (i.e., what could get blocked) is not the same as knowing what real users are actively experiencing (i.e., what is actively getting blocked).

DNS manipulation is an increasingly common technique used by censors and other network adversaries to prevent users from accessing restricted Internet resources and hijack their connections. Prior work in detecting DNS manipulation relies largely on comparing DNS resolutions with trusted control results to identify inconsistencies. However, the emergence of CDNs and other cloud providers practicing content localization and load balancing leads to these heuristics being inaccurate, paving the need for more verifiable signals of DNS manipulation. In this paper, we develop a new technique, CERTainty, that utilizes the widely established TLS certificate ecosystem to accurately detect DNS manipulation, and obtain more information about the adversaries performing such manipulation. We find that untrusted certificates, mismatching hostnames, and blockpages are powerful proxies for detecting DNS manipulation. Our results show that previous work using consistency-based heuristics is inaccurate, allowing for 72.45% false positives in the cases detected as DNS manipulation. Further, we identify 17 commercial DNS filtering products in 52 countries, including products such as SafeDNS, SkyDNS, and Fortinet, and identify the presence of 55 ASes in 26 countries that perform ISP-level DNS manipulation. We also identify 226 new blockpage clusters that are not covered by previous research. We are integrating techniques used by CERTainty into active measurement platforms to continuously and accurately monitor DNS manipulation.

Advances in networking and firewall technology have led to the emergence of network censorship devices that can perform large-scale, highly-performant content blocking. While such devices have proliferated, techniques to locate, identify, and understand them are still limited, require cumbersome manual effort, and are developed on a case-by-case basis.

Remote censorship measurement techniques offer capabilities for monitoring Internet reachability around the world. However, operating these techniques continuously is labor-intensive and requires specialized knowledge and synchronization, leading to limited adoption. In this paper, we introduce Censored Planet, an online censorship measurement platform that collects and analyzes measurements from ongoing deployments of four remote measurement techniques (Augur, Satellite/Iris, Quack, and Hyperquack). Censored Planet adopts a modular design that supports synchronized baseline measurements on six Internet protocols as well as customized measurements that target specific countries and websites. Censored Planet has already collected and published more than 21.8 billion data points of longitudinal network observations over 20 months of operation. Censored Planet complements existing censorship measurement platforms such as OONI and ICLab by offering increased scale, coverage, and continuity. We introduce a new representative censorship metric and show how time series analysis can be applied to Censored Planet's longitudinal measurements to detect 15 prominent censorship events, two-thirds of which have not been reported previously. Using trend analysis, we find increasing censorship activity in more than 100 countries, and we identify 11 categories of websites facing increasing censorship, including provocative attire, human rights issues, and news media. We hope that the continued publication of Censored Planet data helps counter the proliferation of growing restrictions to online freedom.

Increased adoption of HTTPS has created a largely encrypted web, but these security gains are on a collision course with governments that desire visibility into and control over user communications. Last year, the government of Kazakhstan conducted an unprecedented large-scale HTTPS interception attack by forcing users to trust a custom root certificate. We were able to detect the interception and monitor its scale and evolution using measurements from in-country vantage points and remote measurement techniques. We find that the attack targeted connections to 37 unique domains, with a focus on social media and communication services, suggesting a surveillance motive, and that it affected a large fraction of connections passing through the country's largest ISP, Kazakhtelecom. Our continuous real-time measurements indicated that the interception system was shut down after being intermittently active for 21 days. Subsequently, supported by our findings, two major browsers (Mozilla Firefox and Google Chrome) completely blocked the use of Kazakhstan's custom root. However, the incident sets a dangerous precedent, not only for Kazakhstan but for other countries that may seek to circumvent encryption online.