DNSOP D. Migault Internet-Draft Ericsson Intended status: Standards Track D. York Expires: September 28, 2017 Internet Society E. Lewis ICANN March 27, 2017 DNSSEC Validators Requirements draft-mglt-dnsop-dnssec-validator-requirements-04.txt Abstract DNSSEC provides data integrity and authentication for DNSSEC validators. However, without valid trust anchor(s) and an acceptable value for the current time, DNSSEC validation cannot be performed. This document lists the requirements to be addressed so resolvers can have DNSSEC validation can be always-on. 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 http://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 September 28, 2017. Copyright Notice Copyright (c) 2017 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 (http://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 Migault, et al. Expires September 28, 2017 [Page 1] Internet-Draft DNSSEC Validator Requirements March 2017 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Time derivation and absence of Real Time Clock . . . . . . . 3 5. Unplugged devices during Trust Anchor KSKs roll over . . . . 4 6. Emergency Key rollover . . . . . . . . . . . . . . . . . . . 5 6.1. Invalid cached ZSK . . . . . . . . . . . . . . . . . . . 5 6.2. Invalid cached RRSIG . . . . . . . . . . . . . . . . . . 6 6.3. Invalid cached KSK . . . . . . . . . . . . . . . . . . . 6 6.4. Invalid DS . . . . . . . . . . . . . . . . . . . . . . . 6 7. Invalid RRSIG . . . . . . . . . . . . . . . . . . . . . . . . 6 8. Private KSK/ZSK . . . . . . . . . . . . . . . . . . . . . . . 7 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. Security Considerations . . . . . . . . . . . . . . . . . . . 8 11. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 8 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 12.1. Normative References . . . . . . . . . . . . . . . . . . 9 12.2. Informational References . . . . . . . . . . . . . . . . 9 Appendix A. Document Change Log . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Requirements notation 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]. 2. Introduction DNSSEC [RFC4033], [RFC4034], [RFC4035] adds data authentication and integrity checks to DNS [RFC1034], [RFC1035]. For signature validation, DNSSEC requires a valid trust anchor such as the Key Signing Key (KSK) (the Root Zone KSK for example) and an appropriated time. A DNSSEC Validator badly configured may result in disabling DNS resolutions, and then most of the communications relying on the DNS resolution. On the other hand, no standard mechanisms or protocols have been provided to manage DNSSEC Validators. Management of DNSSEC Validators typically includes the ability to check the DNSSEC Migault, et al. Expires September 28, 2017 [Page 2] Internet-Draft DNSSEC Validator Requirements March 2017 configuration, to provision the appropriated trust anchor as well as the ability to recover emergency situation that results in unappropriated data being cached. The lake of management of DNSSEC Validator has slowed down the adoption of DNSSEC. In addition, when deployed, DNSSEC may in fact be deployed in an unsecure way to avoid disturbing communications. Typically successful validation are mentioned while validation failure are bypassed. Although encouraging, these steps are way to small to achieve the ambition of DNSSEC that is securing the DNS. This document describes scenarios where DNSSEC validation cannot be performed properly by the DNSSEC Validator and additiona mechanism is needed. In other words, this means that FQDN properly signed are rejected. From these scenarios, this document derives requirements so DNSSEC Validators can have DNSSEC always activated. Note that the requirements do not indicate how they are fulfilled. More especially, the DNSSEC Validator may implement autonomous mechanism to fulfill these requirements or they may be fulfilled by a third party such as a network administrator. We expect these requirements to be useful to design appropriated protocols for the management of DNSSEC Validator. Once under control risks associated to DNSSEC validation performed improperly will be reduced, thus encouraging activation of DNSSEC Validators. 3. Terminology This document uses the following terminology: - DNSSEC Validator: the entity that performs DNSSEC resolution and performs signature validation. 4. Time derivation and absence of Real Time Clock With M2M communication some devices are not expecting to embed Real Time Clock (Raspberry Pi is one example of such devices). When these devices are re-plugged the initial time is set to January 1 1970. Other devices that have clocks that may suffer from time derivation. All these devices cannot rely on their time estimation to perform DNSSEC validation. REQ1: Mechanism MUST be provided to update the time of the DNSSEC Validator. Migault, et al. Expires September 28, 2017 [Page 3] Internet-Draft DNSSEC Validator Requirements March 2017 5. Unplugged devices during Trust Anchor KSKs roll over In this section we consider a regular Trust Anchor KSK roll over as described in [RFC6781] and [RFC5011]. Unlike regular KSKs, Trust Anchor KSK does not have to update the DS RRset in the parent zone. According to [RFC6781], if TTL_K is the TTL associated to the Trust Anchor KSK and associated RRSIGs, the time of key roll over is around TTL_K with double signed KSKs, and 2 x TTL_K in the case of single singed KSK. The Root Zone KSK is an example of Trust Anchor KSK and at the time of writing the KSK has a TTL of 172800 seconds which means 2 days. This means that 2 days would be sufficient to perform a Trust Anchor KSK roll over. [RFC5011] recommends to advertise the new / old key for 30 days. This means that a device unplugged for two months may not be aware of a regular Trust Anchor KSK rollover. A DNSSEC Validator may be properly configured by the manufacturer to perform DNSSEC validation. The device may for example be configured by the manufacturer shipped to resellers that store the device for a few months, years before selling the devices to the final end user. Similarly, an operational device may remain unplugged for a while for maintenance reason, or held in reserve when a crash occurs. This fall back is never expected to happen and may happen years after. Suppose a KSK complete key roll-over occurs (for example at the Root Zone) while the device is offline. Once plugged again, the device will attempt to validate DNSSEC signature with the old Trust Anchor KSK. The key point in this example is that the device is boot and does not rely on cached information. REQ2: Mechanisms MUST be provided to check the validity of DNSSEC Validator's Trust Anchors. REQ3: Mechanisms MUST be provided to update the Trust Anchor of the DNSSEC Validator. We think these requirements are not restrictive to the Root Zone KSK, but to any KSK. In fact it is not always possible to build a trusted delegation between the Root Zone and any sub zone. This may happen for example if one of the upper zones does not handle the secure delegation or improperly implement it. A DS RRset may not be properly filled or its associated signature cannot be validated. As the chain of trust between a zone and the root zone may not be validated, the DNSSEC validation for the zone requires a Trust Anchor. Such DNS(SEC) resolutions may be critical for infrastructure Migault, et al. Expires September 28, 2017 [Page 4] Internet-Draft DNSSEC Validator Requirements March 2017 management. A company "Example" may for address all its devices under the domain example.com and may not want disruption to happen if the .com delegation cannot be validated for any reason. Such companies may provision there DNSSEC Validator with the Trust Anchor KSK for the zone example.com in addition to the regular DNSSEC delegation. Similarly some some domains may present different views such as a "private" view and a "public view". These zones may have some different content, and may use a different KSK for each view. Note that providing Trust Anchor KSKs is a crucial operation and can be used a vector of attack. As a result, this operation MUST be performed cautiously. 6. Emergency Key rollover Emergency key roll over designates any rollover not performed as described in Section 4.1 of [RFC6781] which results in differences between data stored in the cache of the DNSSEC Validators and the authoritative servers (see section 4.2 in [RFC6781]) Emergency key roll over can be intentionally performed or result from an unexpected behavior in the publishing/validation chain. This is out of scope of this document to understand the reasons/motivations for such key roll over. This document assumes such situation are likely to happen and lists the requirement so DNSSEC Validator can recover from such situations. 6.1. Invalid cached ZSK An emergency ZSK rollover may result in a new ZSK with associated new RRSIG published in the authoritative zone, while DNSSEC Validator may still cache the old value of the ZSK. For a RRset not cached, the DNSSEC Validator performs a DNSSEC query to the authoritative server that returns the RRset signed with the new ZSK. The DNSSEC Validator validates the signature with the old ZSK which results in an invalid signature check. Suppose the old ZSK has been corrupted and that old RRsets have been spoofed. Until the ZSK TTL expires, the DNSSEC Validator considers the spoofed RRsets as valid and the newly signed RRsets as invalid. REQ4: Mechanisms MUST be provided to flush a ZSK from the cache of the DNSSEC Validator. Note that if the DNSSEC Validator receives an indication that a ZSK is not valid anymore, it is expected to flush its cache entries of the old ZSK as well as all entries that have been validated by the Migault, et al. Expires September 28, 2017 [Page 5] Internet-Draft DNSSEC Validator Requirements March 2017 old ZSK. This does not lead to impersonation of ZSK, at most it generates some additional DNSSEC resolutions and validations. 6.2. Invalid cached RRSIG Invalid cached RRSIG would mean the DNSSEC Validator caches a new ZSK, but still has a RRset with a RRSIG signed with the old ZSK. This situation should not happen as when a ZSK is renewed all RRsets validated by the old ZSK are flushed from the cache. 6.3. Invalid cached KSK Consequences of invalid KSK are similar to ZSK. None of the RRSIG can be validated even the one signing the ZSK. (cf. Section 6.1) REQ5: Mechanisms MUST be provided to flush a KSK from the cache of the DNSSEC Validator. 6.4. Invalid DS The DS RRset is stored in the parent zone to build a chain of trust with the child zone. This DS RRset can be invalid because its RDATA (KSK) is not anymore used in the child zone or because the DS is badly signed and cannot be validated by the DNSSEC Validator. In both cases the child zone is considered as insecure and the valid child zone's KSK should become a Trust Anchor KSK. REQ6: Mechanisms MUST be provided to inform the DNSSEC Validator a KSK SHOULD be trusted as a Trust Anchor due to an invalid delegation 7. Invalid RRSIG A zone may have been badly signed, which means that the KSK or ZSK cannot validate the RRSIG associated to the RRsets. This may not be due to a key roll over, but to an incompatibility between the keys (KSK or ZSK) and the signatures. REQ7: Mechanisms MUST be provides to informed the DNSSEC Validator that a KSK or a ZSK MUST NOT be used for RRSIG validation. Unlike "flushing", "MUST NOT be used" means the issue is not a synchronization issue, but that legitimate keys are invalid. Such Keys are known as Negative Trust Anchors [I-D.livingood-negative-trust-anchors]. Migault, et al. Expires September 28, 2017 [Page 6] Internet-Draft DNSSEC Validator Requirements March 2017 This means that the zone for a given time will be known as "known insecure". The DNSSEC Validator is not expected to perform signature validation for this zone. It is expected that this information is associated to a Time To Live (TTL). Note that, this information may be used as an attack vector to impersonate a zone, and must be provided in a trusted way, by a trusted party. If a zone has been badly signed, the administrator of the authoritative DNS server may resign the zone with the same keys or proceed to an emergency key rollover. If the signature is performed with the same keys, the DNSSEC Validator may notice by itself that RRSIG can be validated. On the other hand if a key rollover is performed, the newly received RRSIG will carry a new key id. Upon receiving a new key id in the RRSIG, the DNSSEC Validator is expected to retrieve the new ZSK/KSK. If the RRSIG can be validated, the DNSSEC Validator is expected to remove the "known insecure" flag. However, if the KSK/ZSK are rolled over and RRSIG cannot be validated, it remains hard for the DNSSEC Validator to determine whether the RRSIG cannot be validated or that RRSIG are invalid. As a result: REQ8: Mechanisms MUST be provided to inform the DNSSEC Validator a KSK or a ZSK is known "back to secure". 8. Private KSK/ZSK DNSSEC may also be used in some private environment. Corporate networks and home networks, for example, may want to take advantage of DNSSEC for a local scope network. Typically, a corporate network may use a local scope KSK / ZSK to validate DNS RRsets provided by authoritative DNSSEC server in the corporate network. This use case is also known as the "split-zone" use case. These RRsets within the corporate network may differ from those hosted on the public DNS infrastructure. Note that using different KSK/ZSK for a given zone may expose a zone to signature invalidation. This is especially the case for DNSSEC validators that are expected to flip-flop between local and public scope. How validators have to handle the various provisioned KSK/ZSKs is out of scope of the document. Homenet work may use DNSSEC with TLDs or associated domain names that are of local scope and not even registered in the public DNS infrastructure. REQ9: Mechanisms MUST be provided to inform the DNSSEC Validator a KSK or a ZSK is to be used for private use. Migault, et al. Expires September 28, 2017 [Page 7] Internet-Draft DNSSEC Validator Requirements March 2017 9. IANA Considerations There are no IANA consideration for this document. 10. Security Considerations The requirements listed in this document aim at providing the DNSSEC Validator appropriated information so DNSSEC validation can be performed. On the other hand, providing inappropriate information can lead to misconfiguring the DNSSEC Validator, and thus disrupting the DNSSEC resolution service. As a result, enabling the setting of configuration parameters by a third party may open a wide surface of attacks. As an appropriate time value is necessary to perform signature check (cf. Section 4), an attacker may provide rogue time value to prevent the DNSSEC Validator to check signatures. An attacker may also affect the resolution service by regularly asking the DNSSEC Validator to flush the KSK/ZSK from its cache (cf. Section 6.1 Section 6.3). All associated data will also be flushed. This generates additional DNSSEC resolution and additional validations, as RRSet that were cached require a DNSSEC resolution over the Internet. This affects the resolution service by slowing down responses, and increases the load on the DNSSEC Validator. An attacker may ask the DNSSEC Validator to consider a rogue KSK/ZSK ( cf. Section 6.4, Section 8), thus hijacking the DNS zone. Similarly, (cf. Section 7) an attacker may inform the DNSSEC Validator not to trust a given KSK in order to prevent DNSSEC validation to be performed. An attacker (cf. Section 7) can advertise a "known insecure" KSK or ZSK is "back to secure" to prevent signature check to be performed correctly. As a result, information considered by the DNSSEC Validator should be from a trusted party. This trust party should have been authenticated, and the channel used to exchange the information should also be protected and authenticated. 11. Acknowledgment The need to address DNSSEC issues on the resolver side started in the Home Networks mailing list and during the IETF87 in Berlin. Among others, people involved in the discussion were Ted Lemon, Ralph Weber, Normen Kowalewski, and Mikael Abrahamsson. People involved in Migault, et al. Expires September 28, 2017 [Page 8] Internet-Draft DNSSEC Validator Requirements March 2017 the email discussion initiated by Jim Gettys were, with among others, Paul Wouters, Joe Abley and Michael Richardson. The current document has been initiated after a discussion with Paul Wouter and Evan Hunt. 12. References 12.1. 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, . [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, . [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011, September 2007, . 12.2. Informational References [I-D.livingood-negative-trust-anchors] Livingood, J. and C. Griffiths, "Definition and Use of DNSSEC Negative Trust Anchors", draft-livingood-negative- trust-anchors-07 (work in progress), September 2014. Migault, et al. Expires September 28, 2017 [Page 9] Internet-Draft DNSSEC Validator Requirements March 2017 [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC Operational Practices, Version 2", RFC 6781, DOI 10.17487/RFC6781, December 2012, . Appendix A. Document Change Log [RFC Editor: This section is to be removed before publication] -02: Clarification for private ZSK/KSK. -01: minor editings. -00: First version published. Authors' Addresses Daniel Migault Ericsson 8400 boulevard Decarie Montreal, QC H4P 2N2 Canada Email: daniel.migault@ericsson.com Dan York Internet Society Email: york@isoc.org Edward Lewis ICANN 801 17th Street NW Suite 401 Washington DC, 20006 US USA Email: edward.lewis@icann.org Migault, et al. Expires September 28, 2017 [Page 10]