|Title||Cryptographic Algorithm Identifier Allocation for DNSSEC
Internet Engineering Task Force (IETF) P. Hoffman
Request for Comments: 6014 VPN Consortium
Updates: 4033, 4034, 4035 November 2010
Category: Standards Track
Cryptographic Algorithm Identifier Allocation for DNSSEC
This document specifies how DNSSEC cryptographic algorithm
identifiers in the IANA registries are allocated. It changes the
requirement from "standard required" to "RFC Required". It does not
change the list of algorithms that are recommended or required for
Status of This Memo
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Internet Engineering Steering Group (IESG). Further information on
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[RFC2535] specifies that the IANA registry for DNS Security Algorithm
Numbers be updated by IETF Standards Action only, with the exception
of two values -- 253 and 254. In essence, this means that for an
algorithm to get its own entry in the registry, the algorithm must be
defined in an RFC on the Standards Track as defined in [RFC2026].
The requirement from RFC 2535 is repeated in [RFC3755] and the
combination of [RFC4033], [RFC4034], and [RFC4035].
RFC 2535 allows algorithms that are not on the Standards Track to use
private values 253 and 254 in signatures. In each case, an
unregistered private name must be included with each use of the
algorithm in order to differentiate different algorithms that use the
2. Requirements for Assignments in the DNS Security Algorithm Numbers
This document changes the requirement for registration from requiring
a Standards Track RFC to requiring a published RFC of any type.
There are two reasons for relaxing the requirement:
o There are some algorithms that are useful that may not be able to
be in a Standards Track RFC. For any number of reasons, an
algorithm might not have been evaluated thoroughly enough to be
able to be put on the Standards Track. Another example is that
the algorithm might have unclear intellectual property rights that
prevents the algorithm from being put on the Standards Track.
o Although the size of the registry is restricted (about 250
entries), new algorithms are proposed infrequently. It could
easily be many decades before there is any reason to consider
restricting the registry again.
Some developers will care about the standards level of the RFCs that
are in the registry. The registry has been updated to reflect the
current standards level of each algorithm listed.
To address concerns about the registry eventually filling up, the
IETF should re-evaluate the requirements for entry into this registry
when approximately 120 of the registry entries have been assigned.
That evaluation may lead to tighter restrictions or a new mechanism
for extending the size of the registry. In order to make this
evaluation more likely, IANA has marked about half of the currently
available entries as "Reserved" in order to make the timing for that
re-evaluation more apparent.
The private-use values, 253 and 254, are still useful for developers
who want to test, in private, algorithms for which there is no RFC.
This document does not change the semantics of those two values.
3. Expectations for Implementations
It is important to note that, according to RFC 4034, DNSSEC
implementations are not expected to include all of the algorithms
listed in the IANA registry; in fact, RFC 4034 and the IANA registry
list an algorithm that implementations should not include. This
document does nothing to change the expectation that there will be
items listed in the IANA registry that need not be (and in some
cases, should not be) included in all implementations.
There are many reasons why a DNSSEC implementation might not include
one or more of the algorithms listed, even those on the Standards
Track. In order to be compliant with RFC 4034, an implementation
only needs to implement the algorithms listed as mandatory to
implement in that standard, or updates to that standard. This
document does nothing to change the list of mandatory-to-implement
algorithms in RFC 4034. This document does not change the
requirements for when an algorithm becomes mandatory to implement.
Such requirements should come in a separate, focused document.
It should be noted that the order of algorithms in the IANA registry
does not signify or imply cryptographic strength or preference.
4. IANA Considerations
This document updates allocation requirements for unassigned values
in the "Domain Name System Security (DNSSEC) Algorithm Numbers"
registry located at http://www.iana.org/assignments/
dns-sec-alg-numbers, in the sub-registry titled "DNS Security
Algorithm Numbers". The registration procedure for values that are
assigned after this document is published is "RFC Required".
IANA has marked values 123 through 251 as "Reserved". The registry
notes that this reservation is made in RFC 6014 (this RFC) so that
when most of the unreserved values are taken, future users and IANA
will have a pointer to where the reservation originated and its
IANA has added a textual notation to the "References" column in the
registry that gives the current standards status for each RFC that is
listed in the registry.
5. Security Considerations
An algorithm described in an RFC that is not on the Standards Track
may have weaker security than one that is on the Standards Track; in
fact, that may be the reason that the algorithm was not allowed on
Standards Track. Note, however, that not being on the Standards
Track does not necessarily mean that an algorithm is weaker.
Conversely, algorithms that are on the Standards Track should not
necessarily be considered better than algorithms that are not on the
Standards Track. There are other reasons (such as intellectual
property concerns) that can keep algorithms that are widely
considered to be strong off the Standards Track.
6.1. Normative References
[RFC2535] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
[RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer (DS)", RFC 3755, May 2004.
[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.
6.2. Informative References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
Appendix A. Experimental and Documentation Values
During the early discussion of this document, it was proposed that
maybe there should be a small number of values reserved for
"experimental" purposes. This proposal was not included in this
document because of the long history in the IETF of experimental
values that became permanent. That is, a developer would release
(maybe "experimentally") a version of software that had the
experimental value associated with a particular extension,
competitors would code their systems to test interoperability, and
then no one wanted to change the values in their software to the
"real" value that was later assigned.
There was also a proposal that IANA should reserve two values to be
used in documentation only, similar to the way that "example.com" has
been reserved as a domain name. That proposal was also not included
in this document because all values need to be associated with some
algorithm, and there is no problem with having examples that point to
commonly deployed algorithms.