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.

翻译：近年来，DNS over Encrypted（DoE）方法被视作DNS生态系统领域的新趋势。在这些DoE方法中，DNS over HTTPS（DoH）通过加密保护数据机密性，同时利用与Web服务共享443端口的多路复用技术提供更好的模糊化效果以避免审查。这一发展为发现公开可用的DoH服务带来了某些不便。本文提出E-DoH方法，用于优雅高效地检测DoH服务。首先，我们优化了探测机制，使单个DoH连接能够完成服务发现、正确性验证和依赖构建等多重任务。其次，我们提出了一种高效的DoH检测工具，该工具能在显著降低所需流量的同时提升探测效率。第三，基于上述优化方法，我们对IPv4空间进行了探索，并根据收集的信息对DoH开展了深度分析。实验表明，我们的方法在时间效率上实现了80%的显著提升，且仅需4%-20%的流量即可完成检测任务。在真实环境探测中，我们的方法发现了4.6万个DoH服务，这一数量几乎是现有最先进方法探测结果的两倍。基于收集的数据，我们针对当前DoH服务生态系统提出了若干引人深思的结论。