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Unencrypted DNS traffic between users and DNS resolvers can lead to privacy and security concerns. In response to these privacy risks, many browser vendors have deployed DNS-over-HTTPS (DoH) to encrypt queries between users and DNS resolvers. Today, many client-side deployments of DoH, particularly in browsers, select between only a few resolvers, despite the fact that many more encrypted DNS resolvers are deployed in practice. Unfortunately, if users only have a few choices of encrypted resolver, and only a few perform well from any particular vantage point, then the privacy problems that DoH was deployed to help address merely shift to a different set of third parties. It is thus important to assess the performance characteristics of more encrypted DNS resolvers, to determine how many options for encrypted DNS resolvers users tend to have in practice. In this paper, we explore the performance of a large group of encrypted DNS resolvers supporting DoH by measuring DNS query response times from global vantage points in North America, Europe, and Asia. Our results show that many non-mainstream resolvers have higher response times than mainstream resolvers, particularly for non-mainstream resolvers that are queried from more distant vantage points -- suggesting that most encrypted DNS resolvers are not replicated or anycast. In some cases, however, certain non-mainstream resolvers perform at least as well as mainstream resolvers, suggesting that users may be able to use a broader set of encrypted DNS resolvers than those that are available in current browser configurations.

In this paper, we study the performance of encrypted DNS protocols and conventional DNS from thousands of home networks in the United States, over one month in 2020. We perform these measurements from the homes of 2,693 participating panelists in the Federal Communications Commission's (FCC) Measuring Broadband America program. We found that clients do not have to trade DNS performance for privacy. For certain resolvers, DoT was able to perform faster than DNS in median response times, even as latency increased. We also found significant variation in DoH performance across recursive resolvers. Based on these results, we recommend that DNS clients (e.g., web browsers) should periodically conduct simple latency and response time measurements to determine which protocol and resolver a client should use. No single DNS protocol nor resolver performed the best for all clients., Presented at the Passive and Active Measurement Conference 2021. The final authenticated publication is available online at https://doi.org/10.1007/978-3-030-72582-2_26

Internet censorship measurements rely on lists of websites to be tested, or "block lists" that are curated by third parties. Unfortunately, many of these lists are not public, and those that are tend to focus on a small group of topics, leaving other types of sites and services untested. To increase and diversify the set of sites on existing block lists, we use natural language processing and search engines to automatically discover a much wider range of websites that are censored in China. Using these techniques, we create a list of 1125 websites outside the Alexa Top 1,000 that cover Chinese politics, minority human rights organizations, oppressed religions, and more. Importantly, $\textit{none of the sites we discover are present on the current largest block list}$. The list that we develop not only vastly expands the set of sites that current Internet measurement tools can test, but it also deepens our understanding of the nature of content that is censored in China. We have released both this new block list and the code for generating it.