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Kim et al. J Surveill Secur Saf 2020;1:34-60 I http://dx.doi.org/10.20517/jsss.2020.14 Page 57

Another factor is the support of the Certification Transparency and Certification Authority (CAA) records,
which are techniques to compensate for weaknesses and defects in the PKI-certificate system. While all
organizations provide Certification Transparency, some do not offer CAA records. Regardless of whether
DoH or DoT is supported or not, it is judged as the support of a security solution for certificates.

Almost all providers support DoH and/or DoT, except for Oracle and Verisign. We expect that the support
of the DoH/DoT would increase with time.

Finally, all providers offer TLS 1.2 for cipher transmission, especially Google, Cloudfare, and Quad9 that
support DoH, up to the latest TLS 1.3. Therefore, these institutions are expected to provide more stable
DoH based on TLS 1.3 in the future.

6. DISCUSSION
This paper presents a survey of DNS security. The background of basic DNS and DNSSEC was described,
with an explanation for the motivation of DNSSEC. DNS is essential for proper operation of the Internet,
but it is still subject to a variety of attacks, due to its vulnerabilities, lack of widespread adoption of available
mitigation techniques, and limitations of those techniques. These vulnerabilities were described, and DNS
attacks were classified based on those vulnerabilities. Also, several methods suggested in the literature for
defending against such attacks were summarized.

This survey provides a novel and useful analysis to understand DNS and DNSSEC in terms of cybersecurity.
Specifically, the classification of DNS attacks supports understanding and analysis of future DNS attacks.
This paper provides the first DNS attack classification. The analysis of various mitigation systems also
provides indicators for future DNS developments. Promising alternatives to DNSSEC include DANE/TLSA
and DNS-over-HTTPS. Even lighter-weight approaches, suitable for deployment in the Internet of Things,
are needed as well.

DECLARATIONS
Authors’ contributions
Contributed to the design, survey, implementation, and analysis of the research and to the writing of the
manuscript: Kim TH, Reeves D

Availability of data and materials
Not applicable.

Financial support and sponsorship
Not applicable.

Conflicts of interest
Both authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Copyright
© The Author(s) 2020.