An End-to-End, Large-Scale Measurement of DNS-over-Encryption: How Far Have We Come?

DNS packets are designed to travel in unencrypted form through the Internet based on its initial standard. Recent discoveries show that real-world adversaries are actively exploiting this design vulnerability to compromise Internet users' security and privacy. To mitigate such threats, several protocols have been proposed to encrypt DNS queries between DNS clients and servers, which we jointly term as DNS-over-Encryption. While some proposals have been standardized and are gaining strong support from the industry, little has been done to understand their status from the view of global users. This paper performs by far the first end-to-end and large-scale analysis on DNS-over-Encryption. By collecting data from Internet scanning, user-end measurement and passive monitoring logs, we have gained several unique insights. In general, the service quality of DNS-over-Encryption is satisfying, in terms of accessibility and latency. For DNS clients, DNS-over-Encryption queries are less likely to be disrupted by in-path interception compared to traditional DNS, and the extra overhead is tolerable. However, we also discover several issues regarding how the services are operated. As an example, we find 25% DNS-over-TLS service providers use invalid SSL certificates. Compared to traditional DNS, DNS-over-Encryption is used by far fewer users but we have witnessed a growing trend. As such, we believe the community should push broader adoption of DNS-over-Encryption and we also suggest the service providers carefully review their implementations.