DoH Insight

Over the past few years, a new protocol DNS over HTTPS (DoH) has been created to improve users' privacy on the internet. DoH can be used instead of traditional DNS for domain name translation with encryption as a benefit. This new feature also brings some threats because various security tools depend on readable information from DNS to identify, e.g., malware, botnet communication, and data exfiltration. Therefore, this paper focuses on the possibilities of encrypted traffic analysis, especially on the accurate recognition of DoH. The aim is to evaluate what information (if any) can be gained from HTTPS extended IP flow data using machine learning. We evaluated five popular ML methods to find the best DoH classifiers. The experiments show that the accuracy of DoH recognition is over 99.9 %. Additionally, it is also possible to identify the application that was used for DoH communication, since we have discovered (using created datasets) significant differences in the behavior of Firefox, Chrome, and cloudflared. Our trained classifier can distinguish between DoH clients with the 99.9 % accuracy.