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DNSOP                                                    D. Migault (Ed)
Internet-Draft                                                    Orange
Intended status: Standards Track                         October 7, 2014
Expires: April 10, 2015


                     DNSSEC Validators Requirements
         draft-mglt-dnsop-dnssec-validator-requirements-01.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 April 10, 2015.

Copyright Notice

   Copyright (c) 2014 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
   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.



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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  . . . .   3
   6.  Emergency Key rollover  . . . . . . . . . . . . . . . . . . .   4
     6.1.  Invalid cached ZSK  . . . . . . . . . . . . . . . . . . .   5
     6.2.  Invalid cached RRSIG  . . . . . . . . . . . . . . . . . .   5
     6.3.  Invalid cached KSK  . . . . . . . . . . . . . . . . . . .   6
     6.4.  Invalid DS  . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Invalid RRSIG . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Private KSK . . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   11. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   12. Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .   9
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     13.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     13.2.  Informational References . . . . . . . . . . . . . . . .  10
   Appendix A.  Document Change Log  . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  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.

   Currently few efforts have been made to describe mechanisms that
   guarantee how a DNSSEC validator can be provisioned with the
   appropriated KSKs and time so that DNSSEC validation can always be
   activated.  A device that is badly configured or badly provisioned
   that performs DNSSEC validation may result in disabling the DNS
   service of the device, and then most of its communications.  As a
   result, non administrated devices that implement DNSSEC validation
   always need heuristics to disable the DNSSEC validation.  This
   results in an implicit rule that can be stated as: "if DNSSEC
   validation is performed correctly then do DNSSEC otherwise disable



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   validation and switch to DNS".  In a security point of view, this is
   unacceptable.

   This document considers unmanaged devices performing DNSSEC
   validation and details scenarios where DNSSEC validation cannot be
   performed properly by the device.  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.

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 (Rasberry 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.

   Requirement 1: DNSSEC validator MUST be provided means to
   appropriately update their time.

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 validation may be properly configured by the manufacturer to
   perform DNSSEC validation.  The device may for example be configured



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   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.

   Requirement 2: DNSSEC Validator MUST be able to check the validity of
   their Trust Anchor KSKs.

   Requirement 3: DNSSEC Validator MUST be able to retrieve their Trust
   Anchor KSKs.

   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
   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.

   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

   By emergency key roll over, this paper designates any rollover that
   are not performed as described in Section 4.1 of [RFC6781] and that
   result in differences between data stored in the cache of the DNSSEC
   Validators and the authoritative servers (see section 4.2 in
   [RFC6781])




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   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 that 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.

   Requirement 4: DNSSEC Validator MUST be able to be informed a ZSK
   MUST be flushed from cache.

   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
   old ZSK.  This does not lead to impersonation of ZSK, at most it
   generates some additional DNSSEC resolutions and validations.

   Note also, that constantly inform the DNSSEC Validator of flushing a
   specific ZSK may lead to service disruption.  In order to prevent
   such attacks, the DNSSEC is expected to have mechanisms to limit the
   frequency a zone ZSK can be flushed.  Similarly, informing the DNSSEC
   Validator of flushing randomly chosen ZSK may be associate to
   resource exhaustion attacks, and also affect the resolution service.
   As a result, mechanisms are expected to limit the overall number of
   flushing actions.  These case are detailed in Section 11

6.2.  Invalid cached RRSIG

   This 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.




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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)

   Requirement 5: DNSSEC Validator MUST be able to be informed a KSK
   MUST be flushed from cache.

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.

   Requirement 6: DNSSEC Validator MUST be able to be informed a KSK
   SHOULD be trusted as a Trust Anchor KSK.

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.

   Requirement 7: DNSSEC Validator MUST be able to be informed 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].

   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



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   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 rolledover 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:

   Requirement 8: The DNSSEC Validator MUST be able to be informed that
   a KSK or a ZSK is known "back to secure".

8.  Private KSK

   DNS(SEC) authoritative server are expected to provide public data.
   Corporate networks or home networks may want to provide different
   views for their intranet and the public Internet.  This was commonly
   known as "split-dns".  This means that private networks like home
   networks or corporate networks will not be able to use DNSSEC on the
   private view.

   Requirement 9: DNSSEC Validator MAY be able to be provided KSK for
   private use.

   In that case, the DNSSEC Validator may have two KSKs, one for the DNS
   public view and one for the private view.

9.  Requirements

   The document lists the following requirements:

   - Requirement 1:  DNSSEC validator MUST be provided means to
         appropriately update their time.

   - Requirement 2:  DNSSEC Validator MUST be able to check the validity
         of their Trust Anchor KSKs.

   - Requirement 3:  DNSSEC Validator MUST be able to retrieve their
         Trust Anchor KSKs.

   - Requirement 4:  DNSSEC Validator MUST be able to be informed a ZSK
         MUST be flushed from cache.

   - Requirement 5:  DNSSEC Validator MUST be able to be informed a KSK
         MUST be flushed from cache.





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   - Requirement 6:  DNSSEC Validator MUST be able to be informed a KSK
         SHOULD be trusted as a Trust Anchor KSK.

   - Requirement 7:  DNSSEC Validator MUST be able to be informed that a
         KSK or a ZSK MUST NOT be used for RRSIG validation.

   - Requirement 8:  The DNSSEC Validator MUST be able to be informed
         that a KSK or a ZSK is known "back to secure".

   - Requirement 9:  DNSSEC Validator MUST be able to be provided KSK
         for private use.

10.  IANA Considerations

   There are no IANA consideration for this document.

11.  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.




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   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.

12.  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
   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.

13.  References

13.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, September 2007.







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13.2.  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.

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781, December
              2012.

Appendix A.  Document Change Log

   [RFC Editor: This section is to be removed before publication]

   -00: First version published.

Author's Address

   Daniel Migault
   Orange
   38 rue du General Leclerc
   92794 Issy-les-Moulineaux Cedex 9
   France

   Phone: +33 1 45 29 60 52
   Email: daniel.migault@orange.com
























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