DS Algorithms for Securing NS and Glue

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Author Brian Dickson 
Last updated 2021-09-19
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Network Working Group                                         B. Dickson
Internet-Draft                                                   GoDaddy
Intended status: Informational                         19 September 2021
Expires: 23 March 2022

                 DS Algorithms for Securing NS and Glue


   This Internet Draft proposes a mechanism to encode relevant data for
   NS records on the parental side of a zone cut by encoding them in DS
   records based on a new DNSKEY algorithm.

   Since DS records are signed by the parent, this creates a method for
   validation of the otherwise unsigned delegation records.

   Notably, support for updating DS records in a parent zone is already
   present (by necessity) in the Registry-Registrar-Registrant (RRR)
   provisioning system, EPP.  Thus, no changes to the EPP protocol are
   needed, and no changes to registry database or publication systems
   upstream of the DNS zones published by top level domains (TLDs).

   This NS validation mechanism is beneficial if the name server _names_
   need to be validated prior to use.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 23 March 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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 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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Attack Example  . . . . . . . . . . . . . . . . . . . . .   3
   4.  New DNSKEY Algorithm  . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Algorithm {TBD1}  . . . . . . . . . . . . . . . . . . . .   4
       4.1.1.  Example . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Validation Using These DS Records . . . . . . . . . . . . . .   5
   6.  Protection of glue records  . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   10. Informative References  . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Currently, any query for delegation NS records over an unprotected
   transport path returns results which do not have protection from
   tampering by an active on-path attacker, or against successful cache
   poisoning attackes.  This is because the parent NS records are being
   authoritative, and thus do not have RRSIGs.  The child NS records
   with the same owner name are authoritave, but the parent NS records
   are what get used for delegations.

   There is new privacy work that relies on the name server names in the
   delgation RDATA.  Unsigned records are vulnerable to modification by
   on-path attackers and to cache poisoning by off-path attackers.  That
   privacy work uses the name for TLS validation, and the only source of
   the name server name is the NS record in the delgation.

   This document is about protecting the RDATA of NS record, not the
   privacy issues per se.

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   Note that the use of an encrypted trasport (such as DoT [RFC7858] to
   the parent would be an alternative approach, but in the absence of
   encrypted transport, the current approach is recommended.

   If an attacker alters the NS records returned, or poisons the
   resolver's cache for the unsigned delegation NS, the recursive
   resolver could be directed to a server operated by an attacker.

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Background

   The methods developed for adding security to the Domain Name System,
   collectively refered to as DNSSEC, had as a primary requirement that
   they be backward compatible.  The original specifications for DNS
   used the same Resourc Record Type (RRTYPE) on both the parent and
   child side of a zone cut (the NS record).  The main goal of DNSSEC
   was to ensure data integrity by using cryptographic signatures.
   However, owing to this overlap in the NS record type where the
   records above and below the zone cut have the same owner name created
   an inherent conflict, as only the child zone is authoritative for
   these records.

   The result is that the parent side of the zone cut has records needed
   for DNS resolution which are not signed and not validatable.

   This has no security (data validation) impact on DNS zones which are
   fully DNSSEC signed (anchored at the IANA DNS Trust Anchor), but does
   impact unsigned zones regardless of where the transition from secure
   to insecure occurs.

3.1.  Attack Example

   Suppose a resolver queries for the NS records for "example.com", at
   the name servers for the "com" TLD.  Suppose this domain has been
   published in the com zone as "example.com NS ns1.example.net".

   The response is not protected against MITM attacks.  An on-path
   attacker can substitute its own name, "ns1.attacker.example".  The
   resolver would then send its queries to the attacker.

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   Note that this vulnerability to MITM is present even if the domain
   "example.net" (the domain serving records for "ns1.example.net") is
   DNSSEC signed, and the resolver intends to use TLS to make queries
   for names within the child zone, "example.com".

   Substituting the name server name is sufficient to prevent the
   resolver from validating the TLS connection.  It can validate the
   received TLS certificate, but would do expect the certificate to be
   for "ns1.attacker.example".

4.  New DNSKEY Algorithm

   This new DNSKEY algorithm conforms to the structure requirements from
   [RFC4034], but is not itself used as actual DNSKEY algorithm.  It is
   assigned a value from the DNSKEY algorithm table.  No DNSKEY records
   are published in the child zone using this algorithm.

   This DNSKEY is used only as the input to the corresponding DS hashs
   published in the parent zone.

   Note that this method is orthogonal to the specific choice of DS
   hashes.  Examples here refer to the what is published currently in
   the IANA tables for recommended DNSSEC parameters, including
   recommended choices.  Any valid supported hash for DS records MAY be

4.1.  Algorithm {TBD1}

   This algorithm is used to validate the NS records of the delegation
   for the owner name.

   The original NS records are canonicalized according to the DNSSEC
   signing process [RFC4034] section 6, including removing any label
   compression, and normalizing the character cases to lower case.  The
   RDATA field of the record is hashed using the selected digest
   algorithm(s), e.g.  SHA2-256 for DS digest algorithm 2.

   Note that only the RDATA from the wire format of the original NS
   record is used in constructing the DS record.

4.1.1.  Example

   Consider the delegation in the COM zone:

   example.com NS ns1.Example.Net
   example.com NS ns2.Example.Net

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   The input to the digest for each NS record is the uncompressed wire
   format of their respective RVALUEs.

   The Key Tag is calculated per [RFC4034] using this value as the

   The resulting combination of NS and DS records are:

   example.com NS ns1.Example.Net
   example.com NS ns2.Example.Net
   ; example.com DS KeyTag=FOO Algorithm={TBD1}
   ;   DigestType=2 Digest=sha2-256(wireformat("ns1.example.net"))
   example.com DS KeyTag=FOO Algorithm={TBD1} DigestType=2 Digest=...
   ; example.com DS KeyTag=FOO Algorithm={TBD1}
   ;   DigestType=2 Digest=sha2-256(wireformat("ns2.example.net"))
   example.com DS KeyTag=FOO Algorithm={TBD1} DigestType=2 Digest=...

5.  Validation Using These DS Records

   These new DS records are used to validate corresponding delegation
   records and glue.  Each NS record must have a matching DS record.
   The expected DS record RDATA is constructed, and a matching DS record
   with identical RDATA MUST be present.  Any NS record without matching
   valid DS record MUST be ignored.

   *  NS records are validated using {TBD1}. The RDATA consists of only
      the RDATA from the NS record.

6.  Protection of glue records

   For the issue of glue records (parent side A/AAAA records which are
   not signed), please see the proposal [I-D.dickson-dnsop-glueless].

7.  Security Considerations

   As outlined earlier in FIXME, there could be security issues in
   various use cases.

   The target domain containing each name server name is presumed (and
   required) to be DNSSEC signed.

8.  IANA Considerations

   This document has no IANA actions.  (FIXME - update this doc to
   specify the required IANA actions - add TBD1 to the DNSKEY algorithm

9.  Normative References

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   [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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.  Informative References

              Dickson, B., "Operating a Glueless DNS Authority Server",
              Work in Progress, Internet-Draft, draft-dickson-dnsop-
              glueless-00, 17 September 2021,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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>.

Appendix A.  Acknowledgments

   Thanks to everyone who helped create the tools that let everyone use
   Markdown to create Internet Drafts, and the RFC Editor for xml2rfc.

   Thanks to Dan York for his Tutorial on using Markdown (specifically
   mmark) for writing IETF drafts.

   Thanks to YOUR NAME HERE for contributions, reviews, etc.

Author's Address

   Brian Dickson

   Email: brian.peter.dickson@gmail.com

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