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Network Working Group S. Weiler
Internet-Draft SPARTA, Inc.
Updates: 4033, 4034, 4035, 5155 D. Blacka
(if approved) VeriSign, Inc.
Intended status: Standards Track March 8, 2010
Expires: September 9, 2010
Clarifications and Implementation Notes for DNSSECbis
draft-ietf-dnsext-dnssec-bis-updates-10
Abstract
This document is a collection of technical clarifications to the
DNSSECbis document set. It is meant to serve as a resource to
implementors as well as a repository of DNSSECbis errata.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 9, 2010.
Copyright Notice
Copyright (c) 2010 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
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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 BSD License.
Table of Contents
1. Introduction and Terminology . . . . . . . . . . . . . . . . . 3
1.1. Structure of this Document . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Important Additions to DNSSSECbis . . . . . . . . . . . . . . 3
2.1. NSEC3 Support . . . . . . . . . . . . . . . . . . . . . . 3
2.2. SHA-256 Support . . . . . . . . . . . . . . . . . . . . . 4
3. Security Concerns . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Clarifications on Non-Existence Proofs . . . . . . . . . . 4
3.2. Validating Responses to an ANY Query . . . . . . . . . . . 5
3.3. Check for CNAME . . . . . . . . . . . . . . . . . . . . . 5
3.4. Insecure Delegation Proofs . . . . . . . . . . . . . . . . 5
4. Interoperability Concerns . . . . . . . . . . . . . . . . . . 5
4.1. Errors in Canonical Form Type Code List . . . . . . . . . 5
4.2. Unknown DS Message Digest Algorithms . . . . . . . . . . . 6
4.3. Private Algorithms . . . . . . . . . . . . . . . . . . . . 6
4.4. Caution About Local Policy and Multiple RRSIGs . . . . . . 7
4.5. Key Tag Calculation . . . . . . . . . . . . . . . . . . . 7
4.6. Setting the DO Bit on Replies . . . . . . . . . . . . . . 7
4.7. Setting the AD Bit on Queries . . . . . . . . . . . . . . 8
4.8. Setting the AD Bit on Replies . . . . . . . . . . . . . . 8
4.9. Setting the CD bit on Requests . . . . . . . . . . . . . . 8
4.10. Nested Trust Anchors . . . . . . . . . . . . . . . . . . . 8
4.10.1. Closest Encloser . . . . . . . . . . . . . . . . . . 9
4.10.2. Accept Any Success . . . . . . . . . . . . . . . . . 9
4.10.3. Preference Based on Source . . . . . . . . . . . . . 10
5. Minor Corrections and Clarifications . . . . . . . . . . . . . 10
5.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 10
5.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 10
5.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 11
5.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction and Terminology
This document lists some additions, clarifications and corrections to
the core DNSSECbis specification, as originally described in
[RFC4033], [RFC4034], and [RFC4035], and later amended by [RFC5155].
(See section Section 2 for more recent additions to that core
document set.)
It is intended to serve as a resource for implementors and as a
repository of items that need to be addressed when advancing the
DNSSECbis documents from Proposed Standard to Draft Standard.
1.1. Structure of this Document
The clarifications to DNSSECbis are sorted according to their
importance, starting with ones which could, if ignored, lead to
security problems and progressing down to clarifications that are
expected to have little operational impact.
1.2. Terminology
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. Important Additions to DNSSSECbis
This section lists some documents that should be considered core
DNSSEC protocol documents in addition to those originally specified
in Section 10 of [RFC4033].
2.1. NSEC3 Support
[RFC5155] describes the use and behavior of the NSEC3 and NSEC3PARAM
records for hashed denial of existence. Validator implementations
are strongly encouraged to include support for NSEC3 because a number
of highly visible zones are expected to use it. Validators that do
not support validation of responses using NSEC3 will likely be
hampered in validating large portions of the DNS space.
[RFC5155] should be considered part of the DNS Security Document
Family as described by [RFC4033], Section 10.
Note that the algorithm identifiers defined in RFC5155 (DSA-NSEC3-
SHA1 and RSASHA1-NSEC3-SHA1) signal that a zone MAY be using NSEC3,
rather than NSEC. The zone MAY indeed be using either and validators
supporting these algorithms MUST support both NSEC3 and NSEC
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responses.
2.2. SHA-256 Support
[RFC4509] describes the use of SHA-256 as a digest algorithm in
Delegation Signer (DS) RRs. [RFC5702] describes the use of the
RSASHA256 algorithm in DNSKEY and RRSIG RRs. Validator
implementations are strongly encouraged to include support for this
algorithm for DS, DNSKEY, and RRSIG records.
Both [RFC4509] and [RFC5702] should also be considered part of the
DNS Security Document Family as described by [RFC4033], Section 10.
3. Security Concerns
This section provides clarifications that, if overlooked, could lead
to security issues.
3.1. Clarifications on Non-Existence Proofs
[RFC4035] Section 5.4 under-specifies the algorithm for checking non-
existence proofs. In particular, the algorithm as presented would
incorrectly allow an NSEC or NSEC3 RR from an ancestor zone to prove
the non-existence of RRs in the child zone.
An "ancestor delegation" NSEC RR (or NSEC3 RR) is one with:
o the NS bit set,
o the SOA bit clear, and
o a signer field that is shorter than the owner name of the NSEC RR,
or the original owner name for the NSEC3 RR.
Ancestor delegation NSEC or NSEC3 RRs MUST NOT be used to assume non-
existence of any RRs below that zone cut, which include all RRs at
that (original) owner name other than DS RRs, and all RRs below that
owner name regardless of type.
Similarly, the algorithm would also allow an NSEC RR at the same
owner name as a DNAME RR, or an NSEC3 RR at the same original owner
name as a DNAME, to prove the non-existence of names beneath that
DNAME. An NSEC or NSEC3 RR with the DNAME bit set MUST NOT be used
to assume the non-existence of any subdomain of that NSEC/NSEC3 RR's
(original) owner name.
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3.2. Validating Responses to an ANY Query
[RFC4035] does not address how to validate responses when QTYPE=*.
As described in Section 6.2.2 of [RFC1034], a proper response to
QTYPE=* may include a subset of the RRsets at a given name. That is,
it is not necessary to include all RRsets at the QNAME in the
response.
When validating a response to QTYPE=*, all received RRsets that match
QNAME and QCLASS MUST be validated. If any of those RRsets fail
validation, the answer is considered Bogus. If there are no RRsets
matching QNAME and QCLASS, that fact MUST be validated according to
the rules in [RFC4035] Section 5.4 (as clarified in this document).
To be clear, a validator must not expect to receive all records at
the QNAME in response to QTYPE=*.
3.3. Check for CNAME
Section 5 of [RFC4035] says little about validating responses based
on (or that should be based on) CNAMEs. When validating a NOERROR/
NODATA response, validators MUST check the CNAME bit in the matching
NSEC or NSEC3 RR's type bitmap in addition to the bit for the query
type. Without this check, an attacker could successfully transform a
positive CNAME response into a NOERROR/NODATA response.
3.4. Insecure Delegation Proofs
[RFC4035] Section 5.2 specifies that a validator, when proving a
delegation is not secure, needs to check for the absence of the DS
and SOA bits in the NSEC (or NSEC3) type bitmap. The validator also
needs to check for the presence of the NS bit in the matching NSEC
(or NSEC3) RR (proving that there is, indeed, a delegation), or
alternately make sure that the delegation is covered by an NSEC3 RR
with the Opt-Out flag set. If this is not checked, spoofed unsigned
delegations might be used to claim that an existing signed record is
not signed.
4. Interoperability Concerns
4.1. Errors in Canonical Form Type Code List
When canonicalizing DNS names, DNS names in the RDATA section of NSEC
and RRSIG resource records are not downcased.
[RFC4034] Section 6.2 item 3 has a list of resource record types for
which DNS names in the RDATA are downcased for purposes of DNSSEC
canonical form (for both ordering and signing). That list
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erroneously contains NSEC and RRSIG. According to [RFC3755], DNS
names in the RDATA of NSEC and RRSIG should not be downcased.
The same section also erroneously lists HINFO, and twice at that.
Since HINFO records contain no domain names, they are not subject to
downcasing.
4.2. Unknown DS Message Digest Algorithms
Section 5.2 of [RFC4035] includes rules for how to handle delegations
to zones that are signed with entirely unsupported public key
algorithms, as indicated by the key algorithms shown in those zone's
DS RRsets. It does not explicitly address how to handle DS records
that use unsupported message digest algorithms. In brief, DS records
using unknown or unsupported message digest algorithms MUST be
treated the same way as DS records referring to DNSKEY RRs of unknown
or unsupported public key algorithms.
The existing text says:
If the validator does not support any of the algorithms listed in
an authenticated DS RRset, then the resolver has no supported
authentication path leading from the parent to the child. The
resolver should treat this case as it would the case of an
authenticated NSEC RRset proving that no DS RRset exists, as
described above.
To paraphrase the above, when determining the security status of a
zone, a validator disregards any DS records listing unknown or
unsupported algorithms. If none are left, the zone is treated as if
it were unsigned.
Modified to consider DS message digest algorithms, a validator also
disregards any DS records using unknown or unsupported message digest
algorithms.
4.3. Private Algorithms
As discussed above, section 5.2 of [RFC4035] requires that validators
make decisions about the security status of zones based on the public
key algorithms shown in the DS records for those zones. In the case
of private algorithms, as described in [RFC4034] Appendix A.1.1, the
eight-bit algorithm field in the DS RR is not conclusive about what
algorithm(s) is actually in use.
If no private algorithms appear in the DS set or if any supported
algorithm appears in the DS set, no special processing will be
needed. In the remaining cases, the security status of the zone
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depends on whether or not the resolver supports any of the private
algorithms in use (provided that these DS records use supported hash
functions, as discussed in Section 4.2). In these cases, the
resolver MUST retrieve the corresponding DNSKEY for each private
algorithm DS record and examine the public key field to determine the
algorithm in use. The security-aware resolver MUST ensure that the
hash of the DNSKEY RR's owner name and RDATA matches the digest in
the DS RR. If they do not match, and no other DS establishes that
the zone is secure, the referral should be considered Bogus data, as
discussed in [RFC4035].
This clarification facilitates the broader use of private algorithms,
as suggested by [RFC4955].
4.4. Caution About Local Policy and Multiple RRSIGs
When multiple RRSIGs cover a given RRset, [RFC4035] Section 5.3.3
suggests that "the local resolver security policy determines whether
the resolver also has to test these RRSIG RRs and how to resolve
conflicts if these RRSIG RRs lead to differing results." In most
cases, a resolver would be well advised to accept any valid RRSIG as
sufficient. If the first RRSIG tested fails validation, a resolver
would be well advised to try others, giving a successful validation
result if any can be validated and giving a failure only if all
RRSIGs fail validation.
If a resolver adopts a more restrictive policy, there's a danger that
properly-signed data might unnecessarily fail validation, perhaps
because of cache timing issues. Furthermore, certain zone management
techniques, like the Double Signature Zone-signing Key Rollover
method described in section 4.2.1.2 of [RFC4641] might not work
reliably.
4.5. Key Tag Calculation
[RFC4034] Appendix B.1 incorrectly defines the Key Tag field
calculation for algorithm 1. It correctly says that the Key Tag is
the most significant 16 of the least significant 24 bits of the
public key modulus. However, [RFC4034] then goes on to incorrectly
say that this is 4th to last and 3rd to last octets of the public key
modulus. It is, in fact, the 3rd to last and 2nd to last octets.
4.6. Setting the DO Bit on Replies
As stated in [RFC3225], the DO bit of the query MUST be copied in the
response. At least one implementation has done something different,
so it may be wise for resolvers to be liberal in what they accept.
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4.7. Setting the AD Bit on Queries
The use of the AD bit in the query was previously undefined. This
document defines it as a signal indicating that the requester
understands and is interested in the value of the AD bit in the
response. This allows a requestor to indicate that it understands
the AD bit without also requesting DNSSEC data via the DO bit.
4.8. Setting the AD Bit on Replies
Section 3.2.3 of [RFC4035] describes under which conditions a
validating resolver should set or clear the AD bit in a response. In
order to protect legacy stub resolvers and middleboxes, validating
resolvers SHOULD only set the AD bit when a response both meets the
conditions listed in RFC 4035, section 3.2.3, and the request
contained either a set DO bit or a set AD bit.
4.9. Setting the CD bit on Requests
When processing a request with the CD bit set, a resolver SHOULD
attempt to return all responsive data, even data that has failed
DNSSEC validation. RFC4035 section 3.2.2 requires a resolver
processing a request with the CD bit set to set the CD bit on its
upstream queries.
The guidance in RFC4035 is ambiguous about what to do when a cached
response was obtained with the CD bit not set. In the typical case,
no new query is required, nor does the cache need to track the state
of the CD bit used to make a given query. The problem arises when
the cached response is a server failure (RCODE 2), which may indicate
that the requested data failed DNSSEC validation at an upstream
validating resolver. (RFC2308 permits caching of server failures for
up to five minutes.) In these cases, a new query with the CD bit set
is required.
For efficiency, a validator may wish to set the CD bit on all
upstream queries when it has a trust anchor at or above the QNAME
(and thus can reasonably expect to be able to validate the response).
4.10. Nested Trust Anchors
A DNSSEC validator may be configured such that, for a given response,
more than one trust anchor could be used to validate the chain of
trust to the response zone. For example, imagine a validator
configured with trust anchors for "example." and "zone.example."
When the validator is asked to validate a response to
"www.sub.zone.example.", either trust anchor could apply.
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When presented with this situation, DNSSEC validators have a choice
of which trust anchor(s) to use. Which to use is a matter of
implementation choice. It is possible and perhaps advisable to
expose the choice of policy as a configuration option. The rest of
this section discusses some possible policies. As a default, we
suggest that validators implement the "Accept Any Success" policy
described below in Section 4.10.2 while exposing other policies as
configuration options.
4.10.1. Closest Encloser
One policy is to choose the trust anchor closest to the QNAME of the
response. In our example, that would be the "zone.example." trust
anchor.
This policy has the advantage of allowing the operator to trivially
override a parent zone's trust anchor with one that the operator can
validate in a stronger way, perhaps because the resolver operator is
affiliated with the zone in question. This policy also minimizes the
number of public key operations needed, which may be of benefit in
resource-constrained environments.
This policy has the disadvantage of possibly giving the user some
unexpected and unnecessary validation failures when sub-zone trust
anchors are neglected. As a concrete example, consider a validator
that configured a trust anchor for "zone.example." in 2009 and one
for "example." in 2011. In 2012, "zone.example." rolls its KSK and
updates its DS records, but the validator operator doesn't update its
trust anchor. With the "closest encloser" policy, the validator gets
validation failures.
4.10.2. Accept Any Success
Another policy is to try all applicable trust anchors until one gives
a validation result of Secure, in which case the final validation
result is Secure. If and only if all applicable trust anchors give a
result of Insecure, the final validation result is Insecure. If one
or more trust anchors lead to a Bogus result and there is no Secure
result, then the final validation result is Bogus.
This has the advantage of causing the fewer validation failures,
which may deliver a better user experience. If one trust anchor is
out of date (as in our above example), the user may still be able to
get a Secure validation result (and see DNS responses).
This policy has the disadvantage of making the validator subject to
compromise of the weakest of these trust anchors while making its
relatively painless to keep old trust anchors configured in
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perpetuity.
4.10.3. Preference Based on Source
When the trust anchors have come from different sources (e.g.
automated updates ([RFC5011]), one or more DLV registries
([RFC5074]), and manually configured), a validator may wish to choose
between them based on the perceived reliability of those sources.
The order of precedence might be exposed as a configuration option.
For example, a validator might choose to prefer trust anchors found
in a DLV registry over those manually configured on the theory that
the manually configured ones will not be as aggressively maintained.
Conversely, a validator might choose to prefer manually configured
trust anchors over those obtained from a DLV registry on the theory
that the manually configured ones have been more carefully
authenticated.
Or the validator might do something more complicated: prefer a sub-
set of manually configured trust anchors (based on a configuration
option), then trust anchors that have been updated using the RFC5011
mechanism, then trust anchors from one DLV registry, then trust
anchors from a different DLV registry, then the rest of the manually
configured trust anchors.
5. Minor Corrections and Clarifications
5.1. Finding Zone Cuts
Appendix C.8 of [RFC4035] discusses sending DS queries to the servers
for a parent zone. To do that, a resolver may first need to apply
special rules to discover what those servers are.
As explained in Section 3.1.4.1 of [RFC4035], security-aware name
servers need to apply special processing rules to handle the DS RR,
and in some situations the resolver may also need to apply special
rules to locate the name servers for the parent zone if the resolver
does not already have the parent's NS RRset. Section 4.2 of
[RFC4035] specifies a mechanism for doing that.
5.2. Clarifications on DNSKEY Usage
Questions of the form "can I use a different DNSKEY for signing this
RRset" have occasionally arisen.
The short answer is "yes, absolutely". You can even use a different
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DNSKEY for each RRset in a zone, subject only to practical limits on
the size of the DNSKEY RRset. However, be aware that there is no way
to tell resolvers what a particularly DNSKEY is supposed to be used
for -- any DNSKEY in the zone's signed DNSKEY RRset may be used to
authenticate any RRset in the zone. For example, if a weaker or less
trusted DNSKEY is being used to authenticate NSEC RRsets or all
dynamically updated records, that same DNSKEY can also be used to
sign any other RRsets from the zone.
Furthermore, note that the SEP bit setting has no effect on how a
DNSKEY may be used -- the validation process is specifically
prohibited from using that bit by [RFC4034] section 2.1.2. It is
possible to use a DNSKEY without the SEP bit set as the sole secure
entry point to the zone, yet use a DNSKEY with the SEP bit set to
sign all RRsets in the zone (other than the DNSKEY RRset). It's also
possible to use a single DNSKEY, with or without the SEP bit set, to
sign the entire zone, including the DNSKEY RRset itself.
5.3. Errors in Examples
The text in [RFC4035] Section C.1 refers to the examples in B.1 as
"x.w.example.com" while B.1 uses "x.w.example". This is painfully
obvious in the second paragraph where it states that the RRSIG labels
field value of 3 indicates that the answer was not the result of
wildcard expansion. This is true for "x.w.example" but not for
"x.w.example.com", which of course has a label count of 4
(antithetically, a label count of 3 would imply the answer was the
result of a wildcard expansion).
The first paragraph of [RFC4035] Section C.6 also has a minor error:
the reference to "a.z.w.w.example" should instead be "a.z.w.example",
as in the previous line.
5.4. Errors in RFC 5155
A NSEC3 record that matches an Empty Non-Terminal effectively has no
type associated with it. This NSEC3 record has an empty type bit
map. Section 3.2.1 of [RFC5155] contains the statement:
Blocks with no types present MUST NOT be included.
However, the same section contains a regular expression:
Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+
The plus sign in the regular expression indicates that there is one
or more of the preceding element. This means that there must be at
least one window block. If this window block has no types, it
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contradicts with the first statement. Therefore, the correct text in
RFC 5155 3.2.1 should be:
Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )*
6. IANA Considerations
This document specifies no IANA Actions.
7. Security Considerations
This document adds two cryptographic features to the core DNSSEC
protocol. Additionally, it addresses some ambiguities and omissions
in the core DNSSEC documents that, if not recognized and addressed in
implementations, could lead to security failures. In particular, the
validation algorithm clarifications in Section 3 are critical for
preserving the security properties DNSSEC offers. Furthermore,
failure to address some of the interoperability concerns in Section 4
could limit the ability to later change or expand DNSSEC, including
adding new algorithms.
8. References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC",
RFC 3225, December 2001.
[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.
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[RFC4509] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
(DS) Resource Records (RRs)", RFC 4509, May 2006.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 2008.
[RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY
and RRSIG Resource Records for DNSSEC", RFC 5702,
October 2009.
8.2. Informative References
[RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer (DS)", RFC 3755, May 2004.
[RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
RFC 4641, September 2006.
[RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955,
July 2007.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", RFC 5011, September 2007.
[RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074,
November 2007.
Appendix A. Acknowledgments
The editors would like the thank Rob Austein for his previous work as
an editor of this document.
The editors are extremely grateful to those who, in addition to
finding errors and omissions in the DNSSECbis document set, have
provided text suitable for inclusion in this document.
The lack of specificity about handling private algorithms, as
described in Section 4.3, and the lack of specificity in handling ANY
queries, as described in Section 3.2, were discovered by David
Blacka.
The error in algorithm 1 key tag calculation, as described in
Section 4.5, was found by Abhijit Hayatnagarkar. Donald Eastlake
contributed text for Section 4.5.
The bug relating to delegation NSEC RR's in Section 3.1 was found by
Weiler & Blacka Expires September 9, 2010 [Page 13]
Internet-Draft DNSSECbis Implementation Notes March 2010
Roy Badami. Roy Arends found the related problem with DNAME.
The errors in the [RFC4035] examples were found by Roy Arends, who
also contributed text for Section 5.3 of this document.
The editors would like to thank Alfred Hoenes, Ed Lewis, Danny Mayer,
Olafur Gudmundsson, Suzanne Woolf, and Scott Rose for their
substantive comments on the text of this document.
Authors' Addresses
Samuel Weiler
SPARTA, Inc.
7110 Samuel Morse Drive
Columbia, Maryland 21046
US
Email: weiler@tislabs.com
David Blacka
VeriSign, Inc.
21345 Ridgetop Circle
Dulles, VA 20166
US
Email: davidb@verisign.com
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DNS Extensions working group V.Dolmatov, Ed.
Internet-Draft Cryptocom Ltd.
Intended status: Standards Track March 06, 2010
Expires: September 06, 2010
Use of GOST signature algorithms in DNSKEY and RRSIG Resource Records
for DNSSEC
draft-ietf-dnsext-dnssec-gost-07
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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http://www.ietf.org/ietf/1id-abstracts.txt.
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This Internet-Draft will expire on September 06 2010.
Copyright Notice
Copyright (c) 2009 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.
Abstract
This document describes how to produce signature and hash using
GOST (R 34.10-2001, R 34.11-94) algorithms foor DNSKEY, RRSIG and DS
resource records for use in the Domain Name System Security
Extensions (DNSSEC).
V.Dolmatov Expires September 06, 2010 [Page 1]
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. DNSKEY Resource Records . . . . . . . . . . . . . . . . . . . . 3
2.1. Using a public key with existing cryptographic libraries. . 3
2.2. GOST DNSKEY RR Example . . . . . . . . . . . . . . . . . . 3
3. RRSIG Resource Records . . . . . . . . . . . . . . . . . . . . 4
3.1 RRSIG RR Example . . . . . . . . . . . . . . . . . . . . . . 4
4. DS Resource Records . . . . . . . . . . . . . . . . . . . . . . 5
4.1 DS RR Example . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5
5.1. Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Signature Sizes . . . . . . . . . . . . . . . . . . . . . . 5
5.3. Digest Sizes . . . . . . . . . . . . . . . . . . . . . . . 5
6. Implementation Considerations . . . . . . . . . . . . . . . . . 5
6.1. Support for GOST signatures . . . . . . . . . . . . . . . . 5
6.2. Support for NSEC3 Denial of Existence . . . . . . . . . . . 5
6.3. Byte order . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Security consideration . . . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Domain Name System (DNS) is the global hierarchical distributed
database for Internet Naming. The DNS has been extended to use
cryptographic keys and digital signatures for the verification of the
authenticity and integrity of its data. RFC 4033 [RFC4033], RFC 4034
[RFC4034], and RFC 4035 [RFC4035] describe these DNS Security
Extensions, called DNSSEC.
RFC 4034 describes how to store DNSKEY and RRSIG resource records,
and specifies a list of cryptographic algorithms to use. This
document extends that list with the signature and hash algorithms
GOST [GOST3410, GOST3411],
and specifies how to store DNSKEY data and how to produce
RRSIG resource records with these hash algorithms.
Familiarity with DNSSEC and GOST signature and hash
algorithms is assumed in this document.
The term "GOST" is not officially defined, but is usually used to
refer to the collection of the Russian cryptographic algorithms
GOST R 34.10-2001[DRAFT1], GOST R 34.11-94[DRAFT2],
GOST 28147-89[DRAFT3].
Since GOST 28147-89 is not used in DNSSEC, "GOST" will only refer to
the GOST R 34.10-2001 and GOST R 34.11-94 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].
V.Dolmatov Expires September 06, 2010 [Page 2]
2. DNSKEY Resource Records
The format of the DNSKEY RR can be found in RFC 4034 [RFC4034].
GOST R 34.10-2001 public keys are stored with the algorithm number
{TBA1}.
The wire format of the public key is compatible with
RFC 4491 [RFC4491]:
According to [GOST3410], a public key is a point on the elliptic
curve Q = (x,y).
The wire representation of a public key MUST contain 64 octets,
where the first 32 octets contain the little-endian representation
of x and the second 32 octets contain the little-endian
representation of y.
This corresponds to the binary representation of (<y>256||<x>256)
from [GOST3410], ch. 5.3.
Corresponding public key parameters are those identified by
id-GostR3410-2001-CryptoPro-A-ParamSet (1.2.643.2.2.35.1) [RFC4357],
and the digest parameters are those identified by
id-GostR3411-94-CryptoProParamSet (1.2.643.2.2.30.1) [RFC4357].
2.1. Using a public key with existing cryptographic libraries
Existing GOST-aware cryptographic libraries at the time of this
document writing are capable to read GOST public keys via a generic
X509 API if the key is encoded according to RFC 4491 [RFC4491],
section 2.3.2.
To make this encoding from the wire format of a GOST public key
with the parameters used in this document, prepend the 64 octets
of key data with the following 37-byte sequence:
0x30 0x63 0x30 0x1c 0x06 0x06 0x2a 0x85 0x03 0x02 0x02 0x13 0x30
0x12 0x06 0x07 0x2a 0x85 0x03 0x02 0x02 0x23 0x01 0x06 0x07 0x2a
0x85 0x03 0x02 0x02 0x1e 0x01 0x03 0x43 0x00 0x04 0x40
2.2. GOST DNSKEY RR Example
Given a private key with the following value (the value of GostAsn1
field is split here into two lines to simplify reading; in the
private key file it must be in one line):
Private-key-format: v1.2
Algorithm: {TBA1} (ECC-GOST)
GostAsn1: MEUCAQAwHAYGKoUDAgITMBIGByqFAwICIwEGByqFAwICHgEEIgQgp9c
t2LQaNS1vMKPLEN9zHYjLPNMIQN6QB9vt3AghZFA=
V.Dolmatov Expires September 06, 2010 [Page 3]
The following DNSKEY RR stores a DNS zone key for example.net
example.net. 86400 IN DNSKEY 256 3 {TBA1} (
GtTJjmZKUXV+lHLG/6crB6RCR+EJR51Islpa
6FqfT0MUfKhSn1yAo92+LJ0GDssTiAnj0H0I
9Jrfial/yyc5Og==
) ; key id = 10805
3. RRSIG Resource Records
The value of the signature field in the RRSIG RR follows RFC 4490
[RFC4490] and is calculated as follows. The values for the RDATA
fields that precede the signature data are specified
in RFC 4034 [RFC4034].
hash = GOSTR3411(data)
where "data" is the wire format data of the resource record set
that is signed, as specified in RFC 4034 [RFC4034].
Hash MUST be calculated with GOST R 34.11-94 parameters identified
by id-GostR3411-94-CryptoProParamSet [RFC4357].
Signature is calculated from the hash according to the
GOST R 34.10-2001 standard and its wire format is compatible with
RFC 4490 [RFC4490].
Quoting RFC 4490:
"The signature algorithm GOST R 34.10-2001 generates a digital
signature in the form of two 256-bit numbers, r and s. Its octet
string representation consists of 64 octets, where the first 32
octets contain the big-endian representation of s and the second 32
octets contain the big-endian representation of r."
3.1. RRSIG RR Example
With the private key from section 2.2 sign the following RRSet,
consisting of one A record:
www.example.net. 3600 IN A 192.0.2.1
Setting the inception date to 2000-01-01 00:00:00 UTC and the
expiration date to 2030-01-01 00:00:00 UTC, the following signature
should be created (assuming {TBA1}==249 until proper code is
assigned by IANA)
www.example.net. 3600 IN RRSIG A {TBA1} 3 3600 20300101000000 (
20000101000000 10805 example.net.
k3m0r5bm6kFQmcRlHshY3jIj7KL6KTUsPIAp
Vy466khKuWEUoVvSkqI+9tvMQySQgZcEmS0W
HRFSm0XS5YST5g== )
V.Dolmatov Expires September 06, 2010 [Page 4]
Note: Several ECC-GOST signatures calculated for the same message text
will differ because of using of a random element is used in signature
generation process.
4. DS Resource Records
GOST R 34.11-94 digest algorithm is denoted in DS RRs by the digest
type {TBA2}.The wire format of a digest value is compatible with
RFC4490 [RFC4490], that is digest is in little-endian representation.
The digest MUST always be calculated with GOST R 34.11-94 parameters
identified by id-GostR3411-94-CryptoProParamSet [RFC4357].
4.1. DS RR Example
For key signing key (assuming {TBA1}==249 until proper code is
assigned by IANA)
example.net. 86400 DNSKEY 257 3 {TBA1} (
1aYdqrVz3JJXEURLMdmeI7H1CyTFfPVFBIGA
EabZFP+7NT5KPYXzjDkRbPWleEFbBilDNQNi
q/q4CwA4WR+ovg==
) ; key id = 6204
The DS RR will be
example.net. 3600 IN DS 6204 {TBA1} {TBA2} (
0E6D6CB303F89DBCF614DA6E21984F7A62D08BDD0A05B3A22CC63D1B
553BC61E )
5. Deployment Considerations
5.1. Key Sizes
According to RFC4357 [RFC4357], the key size of GOST public keys
MUST be 512 bits.
5.2. Signature Sizes
According to the GOST signature algorithm specification [GOST3410],
the size of a GOST signature is 512 bits.
5.3. Digest Sizes
According to the GOST R 34.11-94 [GOST3411], the size of a GOST
digest is 256 bits.
6. Implementation Considerations
6.1. Support for GOST signatures
DNSSEC aware implementations MAY be able to support RRSIG and
DNSKEY resource records created with the GOST algorithms as
defined in this document.
V.Dolmatov Expires September 06, 2010 [Page 5]
6.2. Support for NSEC3 Denial of Existence
Any DNSSEC-GOST implementation MUST support both NSEC[RFC4035] and
NSEC3 [RFC5155]
6.3 Byte order
Due to the fact that all existing industry implementations of GOST
cryptographic libraries are returning GOST blobs without
transformation from little-endian format and in order to avoid the
necessity for DNSSEC developers to handle different cryptographic
algorithms differently, it was chosen to send these blobs on the
wire "as is" without transformation of endianness.
7. Security considerations
Currently, the cryptographic resistance of the GOST 34.10-2001
digital signature algorithm is estimated as 2**128 operations
of multiple elliptic curve point computations on prime modulus
of order 2**256.
Currently, the cryptographic resistance of GOST 34.11-94 hash
algorithm is estimated as 2**128 operations of computations of a
step hash function. (There is known method to reduce this
estimate to 2**105 operations, but it demands padding the
colliding message with 1024 random bit blocks each of 256 bit
length, thus it cannot be used in any practical implementation).
8. IANA Considerations
This document updates the IANA registry "DNS Security Algorithm
Numbers" [RFC4034]
(http://www.iana.org/assignments/dns-sec-alg-numbers).
The following entries are added to the registry:
Zone Trans.
Value Algorithm Mnemonic Signing Sec. References Status
{TBA1} GOST R 34.10-2001 ECC-GOST Y * (this memo) OPTIONAL
This document updates the RFC 4034 Digest Types assignment
(section A.2)by adding the value and status for the GOST R 34.11-94
algorithm:
Value Algorithm Status
{TBA2} GOST R 34.11-94 OPTIONAL
9. Acknowledgments
This document is a minor extension to RFC 4034 [RFC4034]. Also, we
tried to follow the documents RFC 3110 [RFC3110], RFC 4509 [RFC4509],
and RFC 4357 [RFC4357] for consistency. The authors of and
contributors to these documents are gratefully acknowledged for
their hard work.
V.Dolmatov Expires September 06, 2010 [Page 6]
The following people provided additional feedback and text: Dmitry
Burkov, Jaap Akkerhuis, Olafur Gundmundsson, Jelte Jansen
and Wouter Wijngaards.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC3110] Eastlake D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain
Name System (DNS)", RFC 3110, May 2001.
[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.
[GOST3410] "Information technology. Cryptographic data security.
Signature and verification processes of [electronic]
digital signature.", GOST R 34.10-2001, Gosudarstvennyi
Standard of Russian Federation, Government Committee of
the Russia for Standards, 2001. (In Russian)
[GOST3411] "Information technology. Cryptographic Data Security.
Hashing function.", GOST R 34.11-94, Gosudarstvennyi
Standard of Russian Federation, Government Committee of
the Russia for Standards, 1994. (In Russian)
[RFC4357] Popov V., Kurepkin I., and S. Leontiev, "Additional
Cryptographic Algorithms for Use with GOST 28147-89,
GOST R 34.10-94, GOST R 34.10-2001, and GOST R 34.11-94
Algorithms", RFC 4357, January 2006.
[RFC4490] S. Leontiev and G. Chudov, "Using the GOST 28147-89,
GOST R 34.11-94, GOST R 34.10-94, and GOST R 34.10-2001
Algorithms with Cryptographic Message Syntax (CMS)",
RFC 4490, May 2006.
[RFC4491] S. Leontiev and D. Shefanovski, "Using the GOST
R 34.10-94, GOST R 34.10-2001, and GOST R 34.11-94
Algorithms with the Internet X.509 Public Key
Infrastructure Certificate and CRL Profile", RFC 4491,
May 2006.
V.Dolmatov Expires September 06, 2010 [Page 7]
[RFC5155] B. Laurie, G. Sisson, R. Arends and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, February 2008.
10.2. Informative References
[RFC4509] Hardaker W., "Use of SHA-256 in DNSSEC Delegation Signer
(DS) Resource Records (RRs)", RFC 4509, May 2006.
[DRAFT1] Dolmatov V., Kabelev D., Ustinov I., Vyshensky S.,
"GOST R 34.10-2001 digital signature algorithm"
draft-dolmatov-cryptocom-gost34102001-08, 12.12.09
work in progress.
[DRAFT2] Dolmatov V., Kabelev D., Ustinov I., Vyshensky S.,
"GOST R 34.11-94 Hash function algorithm"
draft-dolmatov-cryptocom-gost341194-07, 12.12.09
work in progress.
[DRAFT3] Dolmatov V., Kabelev D., Ustinov I., Emelyanova I.,
"GOST 28147-89 encryption, decryption and MAC algorithms"
draft-dolmatov-cryptocom-gost2814789-08, 12.12.09
work in progress.
V.Dolmatov Expires September 06, 2010 [Page 8]
Authors' Addresses
Vasily Dolmatov, Ed.
Cryptocom Ltd.
Kedrova 14, bld.2
Moscow, 117218, Russian Federation
EMail: dol@cryptocom.ru
Artem Chuprina
Cryptocom Ltd.
Kedrova 14, bld.2
Moscow, 117218, Russian Federation
EMail: ran@cryptocom.ru
Igor Ustinov
Cryptocom Ltd.
Kedrova 14, bld.2
Moscow, 117218, Russian Federation
EMail: igus@cryptocom.ru
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