Internet DRAFT - draft-dickson-dnsop-ds-hack
draft-dickson-dnsop-ds-hack
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
draft-dickson-dnsop-ds-hack-02
Abstract
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
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 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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Please review these documents carefully, as they describe your rights
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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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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
used.
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
RDATA.
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
table)
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,
<https://www.rfc-editor.org/info/rfc4034>.
[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
[I-D.dickson-dnsop-glueless]
Dickson, B., "Operating a Glueless DNS Authority Server",
Work in Progress, Internet-Draft, draft-dickson-dnsop-
glueless-00, 17 September 2021,
<https://datatracker.ietf.org/doc/html/draft-dickson-
dnsop-glueless-00>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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
GoDaddy
Email: brian.peter.dickson@gmail.com
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