Internet Engineering Task Force M. Andrews Internet-Draft Internet Systems Consortium Updates: 4034, 4035 (if approved) S. Huque Intended status: Standards Track Salesforce Expires: 25 January 2025 E. Heftrig Fraunhofer Institute 24 July 2024 Collision Free Keytags for DNSSEC draft-huque-dnsop-keytags-00 Abstract DNSSEC employs a Key Tag field in the RRSIG and DS resource records in order to efficiently identify the key that produced a DNSSEC signature and the key that should be used as secure entry point into a delegated zone. The Key Tag was not intended to be a unique identifier. Key tag collisions can occur in practice for keys in the same zone, though they are relatively rare in normal operation. Colliding key tags impose additional work on a validating resolver, which then has to check signatures for each of the candidate set of keys identified by the Key Tag. Furthermore, they open up resolvers to computational denial of service attacks by adversaries deploying specially crafted zones with many intentionally colliding key tags. This document specifies updates to the DNSSEC protocol and the process of key generation to avoid colliding keys and enforce the uniqueness of key tags. Discussion Venues This note is to be removed before publishing as an RFC. Source for this draft and an issue tracker can be found at https://github.com/shuque/ietf-dns-keytags. 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/. Andrews, et al. Expires 25 January 2025 [Page 1] Internet-Draft DNS Greasing July 2024 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 25 January 2025. Copyright Notice Copyright (c) 2024 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Protocol Behavior . . . . . . . . . . . . . . . . . . . . . . 3 3. Updates to RFCs . . . . . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 3 6.1. Normative References . . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . 4 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction DNSSEC [RFC4033] [RFC4034] [RFC4035] employs a Key Tag field in the RRSIG and DS resource records in order to efficiently identify the key that produced a DNSSEC signature the key that should be used as secure entry point into a delegated zone. The Key Tag was not intended to be a unique identifier. Key tag collisions can occur in practice for keys in the same zone, though they are relatively rare in normal operation. Colliding key tags impose additional work on a validating resolver, which then has to check signatures for each of the candidate set of keys identified by the Key Tag. Furthermore, they open up resolvers to computational denial of service attacks by adversaries deploying specially crafted zones with many intentionally colliding key tags [KEYTRAP]. This document specifies updates to the DNSSEC protocol and the process of key generation to avoid colliding Andrews, et al. Expires 25 January 2025 [Page 2] Internet-Draft DNS Greasing July 2024 keys and enforce the uniqueness of key tags. 2. Protocol Behavior * New DNSKEY algorithms MUST have DNSKEY RRsets that do not have colliding key tags * What about existing algorithms? Should we have new aliases for existing algorithms that allow us to incorporate the non collision requirement? * Can we propose a future flag date after which existing algorithms will be required to enforce this requirement? * Outline the general process by which key generation software should ensure uniqueness of keytags. * Special considerations for multi-signer configurations, where multiple distinct parties generate their own keys for the same zone (i) partition the keytag space between each signer/provider, and have each provider re-generate keys if necessary until they obtain one whose keytag is contained in their partition (ii) Use a central key broker to enforce keytag uniqueness, (iii) each signer when generating new keys, queries all DNSKEYs in the multi-signer group to avoid colliding keys. To avoid race conditions, ideally the providers should not generate keys at the same time, and plausibly the zone owner could enforce non-conflicting key generation schedules across the multi-signer group. * Describe what to do when a validator encounters a zone with both old and new DNSKEY algorithm numbers. * For possible discussion: recommend the use DNS cookies to avoid offpath computational DoS attacks. 3. Updates to RFCs TBD 4. Security Considerations Lorem ipsum. 5. IANA Considerations Lorem ipsum. 6. References Andrews, et al. Expires 25 January 2025 [Page 3] Internet-Draft DNS Greasing July 2024 6.1. Normative References [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, DOI 10.17487/RFC4033, March 2005, . [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005, . [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, . 6.2. Informative References [KEYTRAP] Heftrig, E., Schulmann, H., Vogel, N., and M. Waidner, "The KeyTrap Denial-of-Service Algorithmic Complexity Attacks on DNS", . Authors' Addresses Mark Andrews Internet Systems Consortium Email: marka@isc.org Shumon Huque Salesforce Email: shuque@gmail.com Elias Heftrig Fraunhofer Institute Email: elias.heftrig@sit.fraunhofer.de Andrews, et al. Expires 25 January 2025 [Page 4]