



dnsop                                                             L. Pan
Internet-Draft                                          5 September 2025
Intended status: Best Current Practice                                  
Expires: 9 March 2026


       Certificate Transparency (CT) information of DNS resolver
               draft-pan-dnsop-ct-info-of-dns-resolver-00

Abstract

   This document describes the Certificate Transparency (CT) information
   of the DNS resolver.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 9 March 2026.

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Table of Contents

   1.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   2
     3.1.  DNS Resolver Information Keys Registration  . . . . . . .   2
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Background

   DNS resolver can support any encrypted DNS scheme, such as DNS over
   HTTPS (DoH) [RFC8484], DNS over TLS (DoT) [RFC7858], or DNS over QUIC
   (DoQ) [RFC9250].

   Certificate hijacking allows attackers to impersonate a legitimate
   encrypted DNS resolver, see also [MisIssuedCF].

   Certificate Transparency (CT) is to combat the certificate hijacking
   issue [RFC9162].  This document describes the CT information of the
   encrypted DNS resolver.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Basic terms used in this specification are defined in the documents
   [RFC1034], [RFC1035], [RFC9499], [RFC9606], [RFC9162].

3.  IANA Considerations

3.1.  DNS Resolver Information Keys Registration

   [RFC9606] specifies a method for DNS resolvers to publish information
   about themselves.

   IANA has created a new registry called "DNS Resolver Information
   Keys" [IANA-DNS].

   This document adds a new DNS Resolver Information Key: CT, to present
   the CT information of the encrypted DNS resolver.




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   Name: CT

   Value: 1

   Meaning: The value indicates that the certificate of the encrypted
   DNS resolver contains embedded SCTs.

   Reference: RFC 9162

   Name: CT

   Value: 2

   Meaning: The value indicates that the encrypted DNS resolver supports
   the transparency_info TLS extension.

   Reference: RFC 9162

4.  Security Considerations

   DNS clients can get trustworthy DNS resolver information through
   DNSSEC query or out-of-band configuration.

   Suppose the DNS clients find the CT value in the trustworthy DNS
   resolver information.  In that case, they can mandate the CT
   validation in the encrypted communication channel setup process with
   the encrypted DNS resolver.

5.  Acknowledgements

   Thanks to all in the DNSOP mailing list.

6.  References

6.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.



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   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC9162]  Laurie, B., Messeri, E., and R. Stradling, "Certificate
              Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162,
              December 2021, <https://www.rfc-editor.org/info/rfc9162>.

   [RFC9250]  Huitema, C., Dickinson, S., and A. Mankin, "DNS over
              Dedicated QUIC Connections", RFC 9250,
              DOI 10.17487/RFC9250, May 2022,
              <https://www.rfc-editor.org/info/rfc9250>.

   [RFC9499]  Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
              RFC 9499, DOI 10.17487/RFC9499, March 2024,
              <https://www.rfc-editor.org/info/rfc9499>.

   [RFC9606]  Reddy.K, T. and M. Boucadair, "DNS Resolver Information",
              RFC 9606, DOI 10.17487/RFC9606, June 2024,
              <https://www.rfc-editor.org/info/rfc9606>.

6.2.  Informative References

   [IANA-DNS] IANA, "Domain Name System (DNS) Parameters", n.d.,
              <https://www.iana.org/assignments/dns-parameters/>.

   [MisIssuedCF]
              Goodin, D., "Mis-issued certificates for 1.1.1.1 DNS
              service pose a threat to the Internet", 2025,
              <https://arstechnica.com/security/2025/09/mis-issued-
              certificates-for-1-1-1-1-dns-service-pose-a-threat-to-the-
              internet/>.

Author's Address

   Lanlan Pan
   Guangdong
   China
   Email: abbypan@gmail.com







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