E-DoH: Elegantly Detecting the Depths of Open DoH Service on the Internet

TL;DR

This paper introduces E-DoH, an optimized method for detecting DoH services that significantly improves efficiency and reduces traffic, leading to the discovery of nearly twice as many services as previous methods.

Contribution

The paper presents an innovative, optimized detection approach for DoH services that enhances efficiency and accuracy over existing techniques.

Findings

80% improvement in detection time efficiency

Discovered 46,000 DoH services, nearly double previous methods

Reduced traffic volume to 4-20% of prior requirements

Abstract

In recent years, DNS over Encrypted (DoE) methods have been regarded as a novel trend within the realm of the DNS ecosystem. In these DoE methods, DNS over HTTPS (DoH) provides encryption to protect data confidentiality while providing better obfuscation to avoid censorship by multiplexing port 443 with web services. This development introduced certain inconveniences in discovering publicly available DoH services. In this paper, we propose the E-DoH method for elegant and efficient DoH service detection. First, we optimized the probing mechanism to enable a single DoH connection to accomplish multiple tasks including service discovery, correctness validation and dependency construction. Second, we propose an efficient DoH detection tool. This tool can enhance probing efficiency while significantly reduce the required traffic volume. Third, based on the above optimization methods, we conducted an exploration of the IPv4 space and performed an in-depth analysis of DoH based on the collected information. Through experiments, our approach demonstrates a remarkable 80% improvement in time efficiency, and only requires 4%-20% traffic volume to complete the detection task. In wild detection, our approach discovered 46k DoH services, which nearly doubles the number discovered by the state-of-the-art. Based on the collected data, we present several intriguing conclusions about the current DoH service ecosystem.