dnsop P. Wouters
Internet-Draft Red Hat
Obsoletes: 6944 (if approved) O. Sury
Intended status: Standards Track CZ.NIC
Expires: April 14, 2017 October 11, 2016
Algorithm Implementation Requirements and Usage Guidance for DNSSEC
draft-wouters-sury-dnsop-algorithm-update-02
Abstract
The DNSSEC protocol makes use of various cryptographic algorithms in
order to provide authentication of DNS data and proof of non-
existence. To ensure interoperability between DNS resolvers and DNS
authoritative servers, it is necessary to specify a set of algorithm
implementation requirements and usage guidance to ensure that there
is at least one algorithm that all implementations support. This
document defines the current algorithm implementation requirements
and usage guidance for DNSSEC. This document obsoletes RFC-6944.
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 14, 2017.
Copyright Notice
Copyright (c) 2016 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
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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
1.1. Updating Algorithm Implementation Requirements and Usage
Guidance . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Updating Algorithm Requirement Levels . . . . . . . . . . 2
1.3. Document Audience . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 4
3.1. DNSKEY Algorithms . . . . . . . . . . . . . . . . . . . . 4
3.2. DS and CDS Algorithms . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. Operational Considerations . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The DNSSEC signing algorithms are defined by various RFCs, including
[RFC4034], [RFC5155], [RFC5702], [RFC5933], [RFC6605],
[I-D.ietf-curdle-dnskey-eddsa]. DNSSEC is used to provide
authentication of data. To ensure interoperability, a set of
"mandatory-to-implement" DNSKEY algorithms are defined. This
document obsoletes [RFC6944].
1.1. Updating Algorithm Implementation Requirements and Usage Guidance
The field of cryptography evolves continuously. New stronger
algorithms appear and existing algorithms are found to be less secure
then originally thought. Therefore, algorithm implementation
requirements and usage guidance need to be updated from time to time
to reflect the new reality. The choices for algorithms must be
conservative to minimize the risk of algorithm compromise.
1.2. Updating Algorithm Requirement Levels
The mandatory-to-implement algorithm of tomorrow should already be
available in most implementations of DNSSEC by the time it is made
mandatory. This document attempts to identify and introduce those
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algorithms for future mandatory-to-implement status. There is no
guarantee that the algorithms in use today may become mandatory in
the future. Published algorithms are continuously subjected to
cryptographic attack and may become too weak or could become
completely broken before this document is updated.
This document only provides recommendations for the mandatory-to-
implement algorithms or algorithms too weak that are recommended not
to be implemented. As a result, any algorithm listed at the
[DNSKEY-IANA] and [DS-IANA] registries not mentioned in this document
MAY be implemented. For clarification and consistency, an algorithm
will be set to MAY only when it has been downgraded.
Although this document updates the algorithms to keep the DNSSEC
authentication secure over time, it also aims at providing
recommendations so that DNSSEC implementations remain interoperable.
DNSSEC interoperability is addressed by an incremental introduction
or deprecation of algorithms.
It is expected that deprecation of an algorithm is performed
gradually. This provides time for various implementations to update
their implemented algorithms while remaining interoperable. Unless
there are strong security reasons, an algorithm is expected to be
downgraded from MUST to MUST- or SHOULD, instead of MUST NOT.
Similarly, an algorithm that has not been mentioned as mandatory-to-
implement is expected to be introduced with a SHOULD instead of a
MUST.
Since the effects of using an unknown DNSKEY algorithm is for the
zone to be treated as insecure, it is recommended that algorithms
downgraded to SHOULD- or below are no longer used by authoritative
nameservers and DNSSEC signers to create new DNSKEY's. This will
allow for algorithms to slowly become more unused over time. Once
deployment has reached a sufficiently low point these algorithms can
finally be marked as MUST NOT so that recursive nameservers can
remove support for these algorithms.
Recursive nameservers are encouraged to keep support for all
algorithms not marked as MUST NOT.
1.3. Document Audience
The recommendations of this document mostly target DNSSEC
implementers as implementations need to meet both high security
expectations as well as high interoperability between various vendors
and with different versions. Interoperability requires a smooth move
to more secure algorithms. This may differ from a user point of view
that may deploy and configure DNSSEC with only the safest algorithm.
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On the other hand, comments and recommendations from this document
are also expected to be useful for such users.
2. Conventions Used in This Document
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].
We define some additional terms here:
SHOULD+ This term means the same as SHOULD. However, it is likely
that an algorithm marked as SHOULD+ will be promoted at
some future time to be a MUST.
SHOULD- This term means the same as SHOULD. However, an algorithm
marked as SHOULD- may be deprecated to a MAY in a future
version of this document.
MUST- This term means the same as MUST. However, it is expected
at some point in the near future that this algorithm will
no longer be a MUST in a future document. Although its
status will be determined at a later time, it is reasonable
to expect that if a future revision of a document alters
the status of a MUST- algorithm, it will remain at least a
SHOULD or a SHOULD-.
3. Algorithm Selection
3.1. DNSKEY Algorithms
Recommendations for DNSKEY algorithms [DNSKEY-IANA]
+--------+--------------------+----------------+-------------------+
| Number | Mnemonics | DNSSEC Signing | DNSSEC Validation |
+--------+--------------------+----------------+-------------------+
| 1 | RSAMD5 | MUST NOT | MUST NOT |
| 3 | DSA | MUST NOT | MUST NOT |
| 5 | RSASHA1 | MUST- | MUST- |
| 6 | DSA-NSEC3-SHA1 | MUST NOT | MUST NOT |
| 7 | RSASHA1-NSEC3-SHA1 | MUST- | MUST- |
| 8 | RSASHA256 | MUST | MUST |
| 10 | RSASHA512 | SHOULD- | MUST |
| 12 | ECC-GOST | SHOULD NOT | SHOULD- |
| 13 | ECDSAP256SHA256 | SHOULD- | MUST- |
| 14 | ECDSAP384SHA384 | SHOULD NOT | SHOULD- |
| TBD | ED25519 | SHOULD+ | SHOULD+ |
| TBD | ED448 | SHOULD+ | SHOULD+ |
+--------+--------------------+----------------+-------------------+
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RSAMD5 is not widely deployed and there is an industry-wide trend to
deprecate MD5 usage.
RSASHA1 and RSASHA1-NSEC3-SHA1 are widely deployed, although zones
deploying it are recommended to switch to RSASHA256 as there is an
industry-wide trend to deprecate SHA1 usage. RSASHA1 does not
support NSEC3. RSASHA1-NSEC3-SHA1 can be used with or without NSEC3.
DSA and DSA-NSEC3-SHA1 are not widely deployed and vulnerable to
private key compromise when generating signatures using a weak or
compromised random number generator.
RSASHA512 is at the SHOULD level for DNSSEC Signing because it has
not seen wide deployment, but there are some deployments hence DNSSEC
Validation MUST implement RSASHA512 to ensure interoperability.
ECC-GOST is at the SHOULD NOT level because it has not seen wide
deployment and the algorithm has not seen wide scrutiny in the crypto
community.
ECDSAP256SHA256 and ECDSAP384SHA384 provide more strength for
signature size than RSASHA256 and RSASHA512 variants.
ECDSAP256SHA256 has seen increased deployment and has been raised to
MUST- level for resolving and SHOULD- for signing. It is seen as a
temporary improvement over RSA until the
[I-D.ietf-curdle-dnskey-eddsa] algorithms are published, implemented
and deployed. ECDSAP384SHA384 offers little over ECDSAP256SHA256 and
has not seen wide deployment, so the use is discouraged, especially
for signing.
ED25519 and ED448 uses Edwards-curve Digital Security Algorithm
(EdDSA). There are three main advantages of the EdDSA algorithm: It
does not require the use of a unique random number for each
signature, there are no padding or truncation issues as with ECDSA,
and it is more resilient to side-channel attacks. Hence it is
expected that these algorithms will be raised to SHOULD for signing
and MUST for resolving once it has seen more implementations and
deployement.
3.2. DS and CDS Algorithms
Recommendations for Delegation Signer Digest Algorithms [DNSKEY-IANA]
These also apply to the CDS RRTYPE as specified in [RFC7344]
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+--------+-----------------+-------------------+-------------------+
| Number | Mnemonics | DNSSEC Delegation | DNSSEC Validation |
+--------+-----------------+-------------------+-------------------+
| 0 | NULL (CDS only) | MUST NOT [*] | MUST NOT [*] |
| 1 | SHA-1 | SHOULD NOT | MUST- |
| 2 | SHA-256 | MUST | MUST |
| 3 | GOST R 34.11-94 | MAY | SHOULD |
| 4 | SHA-384 | MAY | SHOULD+ |
+--------+-----------------+-------------------+-------------------+
[*] - This is a special type of CDS record signaling removal of DS at
the parent in [I-D.ietf-dnsop-maintain-ds]
NULL is a special case, see [I-D.ietf-dnsop-maintain-ds]
SHA-1 is in wide use for DS records, but its use is discouraged as it
is an aging algorithm. Users of SHA-1 SHOULD upgrade to SHA-256.
SHA-256 is in wide use and considered strong.
GOST R 34.11-94 is not in wide use. It is still recommended to be
supported in validators so that adoption can increase.
SHA-384 is not in wide use. It is still recommended to be supported
in validators so that adoption can increase.
4. Security Considerations
The security of cryptographic-based systems depends on both the
strength of the cryptographic algorithms chosen and the strength of
the keys used with those algorithms. The security also depends on
the engineering of the protocol used by the system to ensure that
there are no non-cryptographic ways to bypass the security of the
overall system.
This document concerns itself with the selection of cryptographic
algorithms for the use of DNSSEC, specifically with the selection of
"mandatory-to-implement" algorithms. The algorithms identified in
this document as "MUST implement" or "SHOULD implement" are not known
to be broken at the current time, and cryptographic research so far
leads us to believe that they will likely remain secure into the
foreseeable future. However, this isn't necessarily forever and it
is expected that new revisions of this document will be issued from
time to time to reflect the current best practice in this area.
Retiring an algorithm too soon would result in a signed zone with
such an algorithm to be downgraded to the equivalent of an unsigned
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zone. Therefore, algorithm deprecation must be done very slowly and
only after careful consideration and measurements of its use.
5. Operational Considerations
DNSKEY algorithm rollover in a live zone is a complex process. See
[RFC6781] and [RFC7583] for guidelines on how to perform algorithm
rollovers.
6. IANA Considerations
This document makes no requests of IANA.
7. Acknowledgements
This document borrows text from RFC 4307 by Jeffrey I. Schiller of
the Massachusetts Institute of Technology (MIT) and the 4307bis
document by Yoav Nir, Tero Kivinen, Paul Wouters and Daniel Migault.
Much of the original text has been copied verbatim.
We wish to thank Olafur Gudmundsson and Paul Hoffman for their
imminent feedback.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References
[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,
<http://www.rfc-editor.org/info/rfc4034>.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
<http://www.rfc-editor.org/info/rfc5155>.
[RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY
and RRSIG Resource Records for DNSSEC", RFC 5702,
DOI 10.17487/RFC5702, October 2009,
<http://www.rfc-editor.org/info/rfc5702>.
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[RFC5933] Dolmatov, V., Ed., Chuprina, A., and I. Ustinov, "Use of
GOST Signature Algorithms in DNSKEY and RRSIG Resource
Records for DNSSEC", RFC 5933, DOI 10.17487/RFC5933, July
2010, <http://www.rfc-editor.org/info/rfc5933>.
[RFC6605] Hoffman, P. and W. Wijngaards, "Elliptic Curve Digital
Signature Algorithm (DSA) for DNSSEC", RFC 6605,
DOI 10.17487/RFC6605, April 2012,
<http://www.rfc-editor.org/info/rfc6605>.
[RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
Operational Practices, Version 2", RFC 6781,
DOI 10.17487/RFC6781, December 2012,
<http://www.rfc-editor.org/info/rfc6781>.
[RFC6944] Rose, S., "Applicability Statement: DNS Security (DNSSEC)
DNSKEY Algorithm Implementation Status", RFC 6944,
DOI 10.17487/RFC6944, April 2013,
<http://www.rfc-editor.org/info/rfc6944>.
[RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
DNSSEC Delegation Trust Maintenance", RFC 7344,
DOI 10.17487/RFC7344, September 2014,
<http://www.rfc-editor.org/info/rfc7344>.
[RFC7583] Morris, S., Ihren, J., Dickinson, J., and W. Mekking,
"DNSSEC Key Rollover Timing Considerations", RFC 7583,
DOI 10.17487/RFC7583, October 2015,
<http://www.rfc-editor.org/info/rfc7583>.
[I-D.ietf-curdle-dnskey-eddsa]
Sury, O. and R. Edmonds, "EdDSA for DNSSEC", draft-ietf-
curdle-dnskey-eddsa-01 (work in progress), October 2016.
[I-D.ietf-dnsop-maintain-ds]
Gudmundsson, O. and P. Wouters, "Managing DS records from
parent via CDS/CDNSKEY", draft-ietf-dnsop-maintain-ds-03
(work in progress), June 2016.
[DNSKEY-IANA]
"DNSKEY Algorithms", <http://www.iana.org/assignments/
dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml>.
[DS-IANA] "Delegation Signer Digest Algorithms",
<http://www.iana.org/assignments/ds-rr-types/
ds-rr-types.xhtml>.
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Authors' Addresses
Paul Wouters
Red Hat
EMail: pwouters@redhat.com
Ondrej Sury
CZ.NIC
EMail: ondrej.sury@nic.cz
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