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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 9 March 2026. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Pan Expires 9 March 2026 [Page 1] Internet-Draft EFAS September 2025 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. Pan Expires 9 March 2026 [Page 2] Internet-Draft EFAS September 2025 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, . [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Pan Expires 9 March 2026 [Page 3] Internet-Draft EFAS September 2025 [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, . [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, . [RFC9162] Laurie, B., Messeri, E., and R. Stradling, "Certificate Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162, December 2021, . [RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over Dedicated QUIC Connections", RFC 9250, DOI 10.17487/RFC9250, May 2022, . [RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219, RFC 9499, DOI 10.17487/RFC9499, March 2024, . [RFC9606] Reddy.K, T. and M. Boucadair, "DNS Resolver Information", RFC 9606, DOI 10.17487/RFC9606, June 2024, . 6.2. Informative References [IANA-DNS] IANA, "Domain Name System (DNS) Parameters", n.d., . [MisIssuedCF] Goodin, D., "Mis-issued certificates for 1.1.1.1 DNS service pose a threat to the Internet", 2025, . Author's Address Lanlan Pan Guangdong China Email: abbypan@gmail.com Pan Expires 9 March 2026 [Page 4]