Identifying the Phishing Websites Using the Patterns of TLS Certificates

Keywords: TLS Certificate, Phishing, Web security


With the recent rise of HTTPS adoption on the Web, attackers have begun “HTTPSifying” phishing websites. HTTPSifying a phishing website has the advantage of making the website appear legitimate and evading conventional detection methods that leverage URLs or web contents in the network. Further, adopting HTTPS could also contribute to generating intrinsic footprints and provide defenders with a great opportunity to monitor and detect websites, including phishing sites, as they would need to obtain a public-key certificate issued for the preparation of the websites. The potential benefits of certificate-based detection include (1) the comprehensive monitoring of all HTTPSified websites by using certificates immediately after their issuance, even if the attacker utilizes dynamic DNS (DDNS) or hosting services; this could be overlooked with the conventional domain-registration-based approaches; and (2) to detect phishing websites before they are published on the Internet. Accordingly, we address the following research question: How can we make use of the footprints of TLS certificates to defend against phishing attacks? For this, we collected a large set of TLS certificates corresponding to phishing websites from Certificate Transparency (CT) logs and extensively analyzed these TLS certificates. We demonstrated that a template of common names, which are equivalent to the fully qualified domain names, obtained through the clustering analysis of the certificates can be used for the following promising applications: (1) The discovery of previously unknown phishing websites and (2) understanding the infrastructure used to generate the phishing websites. Furthermore, we developed a real-time monitoring system using the analysis techniques. We demonstrate its usefulness for the practical security operation. We use our findings on the abuse of free certificate authorities (CAs) for operating HTTPSified phishing websites to discuss possible solutions against such abuse and provide a recommendation to the CAs.


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Author Biographies

Yuji Sakurai, Waseda University, Shinjuku City, Tokyo, Japan

Yuji Sakurai received a B.E degree in computer science and communication from Waseda University, affiliated with the Network Security Lab. His interests include Network Security, and Internet Measurement.

Takuya Watanabe, NTT Secure Platform Laboratories, Japan

Takuya Watanabe received B.E. and M.E. degrees in computer science and engineering, and Ph.D. degree in engineering from the Waseda University, in 2014, 2016, and 2020, respectively. Since joining Nippon Telegraph and Telephone Corporation (NTT) in 2016, he has been engaged in research of consumer security and privacy. He is now with the Cyber Security Project of NTT Secure Platform Laboratories.

Tetsuya Okuda, NTT Secure Platform Laboratories, Japan

Tetsuya Okuda received B.E. and M.E. degrees in aeronautics and astronautics from the Tokyo University in 2009, 2011, respectively. Since joining Nippon Telegraph and Telephone Corporation (NTT) in 2011, he has been engaged in research and engineering of data security and web services. He is now with the Data Security Project of NTT Secure Platform Laboratories.

Mitsuaki Akiyama, NTT Secure Platform Laboratories, Japan

Mitsuaki Akiyama received his M.E. and Ph.D. degrees in information science from Nara Institute of Science and Technology, Japan in 2007 and 2013. Since joining Nippon Telegraph and Telephone Corporation (NTT) in 2007, he has been engaged in research and development on cybersecurity. He is currently a Senior Distinguished Researcher with the Cyber Security Project of NTT Secure Platform Laboratories. His research interests include cybersecurity measurement, offensive security, and usable security and privacy. He is a member of the IEEE, IPSJ, and IEICE.

Tatsuya Mori, Waseda University, Shinjuku City, Tokyo, Japan; NICT, Japan

Tatsuya Mori is currently a professor at Waseda University, Tokyo, Japan. He received B.E. and M.E. degrees in applied physics, and Ph.D. degree in information science from the Waseda University, in 1997, 1999 and 2005, respectively. He joined NTT lab in 1999. Since then, he has been engaged in the research of measurement and analysis of networks and cyber security. From Mar 2007 to Mar 2008, he was a visiting researcher at the University of Wisconsin-Madison. He received Telecom System Technology Award from TAF in 2010 and Best Paper Awards from IEICE and IEEE/ACM COMSNETS in 2009 and 2010, respectively. Dr. Mori is a member of ACM, IEEE, IEICE, IPSJ, and USENIX.



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