draft-ietf-dnsext-ds-sha256-05.txt   rfc4509.txt 
Network Working Group W. Hardaker Network Working Group W. Hardaker
Internet-Draft Sparta Request for Comments: 4509 Sparta
Expires: August 25, 2006 February 21, 2006 Category: Standards Track May 2006
Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records (RRs) Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records (RRs)
draft-ietf-dnsext-ds-sha256-05.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document specifies how to use the SHA-256 digest type in DNS This document specifies how to use the SHA-256 digest type in DNS
Delegation Signer (DS) Resource Records (RRs). DS records, when Delegation Signer (DS) Resource Records (RRs). DS records, when
stored in a parent zone, point to key signing DNSKEY key(s) in a stored in a parent zone, point to DNSKEYs in a child zone.
child zone.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................2
2. Implementing the SHA-256 algorithm for DS record support . . . 3 2. Implementing the SHA-256 Algorithm for DS Record Support ........2
2.1. DS record field values . . . . . . . . . . . . . . . . . . 3 2.1. DS Record Field Values .....................................2
2.2. DS Record with SHA-256 Wire Format . . . . . . . . . . . . 3 2.2. DS Record with SHA-256 Wire Format .........................3
2.3. Example DS Record Using SHA-256 . . . . . . . . . . . . . . 4 2.3. Example DS Record Using SHA-256 ............................3
3. Implementation Requirements . . . . . . . . . . . . . . . . . . 4 3. Implementation Requirements .....................................3
4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4 4. Deployment Considerations .......................................4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations .............................................4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations .........................................4
6.1. Potential Digest Type Downgrade Attacks . . . . . . . . . . 5 6.1. Potential Digest Type Downgrade Attacks ....................4
6.2. SHA-1 vs SHA-256 Considerations for DS Records . . . . . . 6 6.2. SHA-1 vs SHA-256 Considerations for DS Records .............5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements ................................................5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. References ......................................................6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References .......................................6
8.2. Informative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References .....................................6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 9
1. Introduction 1. Introduction
The DNSSEC [RFC4033] [RFC4034] [RFC4035] DS RR is published in parent The DNSSEC [RFC4033] [RFC4034] [RFC4035] DS RR is published in parent
zones to distribute a cryptographic digest of a child's Key Signing zones to distribute a cryptographic digest of one key in a child's
Key (KSK) DNSKEY RR. The DS RRset is signed by at least one of the DNSKEY RRset. The DS RRset is signed by at least one of the parent
parent zone's private zone data signing keys for each algorithm in zone's private zone data signing keys for each algorithm in use by
use by the parent. Each signature is published in an RRSIG resource the parent. Each signature is published in an RRSIG resource record,
record, owned by the same domain as the DS RRset and with a type owned by the same domain as the DS RRset, with a type covered of DS.
covered of DS.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
document are to be interpreted as described in [RFC2119]. and "OPTIONAL" are to be interpreted as described in [RFC2119].
2. Implementing the SHA-256 algorithm for DS record support 2. Implementing the SHA-256 Algorithm for DS Record Support
This document specifies that the digest type code [XXX: To be This document specifies that the digest type code 2 has been assigned
assigned by IANA; likely 2] is to be assigned to SHA-256 [SHA256] to SHA-256 [SHA256] [SHA256CODE] for use within DS records. The
[SHA256CODE] for use within DS records. The results of the digest results of the digest algorithm MUST NOT be truncated, and the entire
algorithm MUST NOT be truncated and the entire 32 byte digest result 32 byte digest result is to be published in the DS record.
is to be published in the DS record.
2.1. DS record field values 2.1. DS Record Field Values
Using the SHA-256 digest algorithm within a DS record will make use Using the SHA-256 digest algorithm within a DS record will make use
of the following DS-record fields: of the following DS-record fields:
Digest type: [XXX: To be assigned by IANA; likely 2] Digest type: 2
Digest: A SHA-256 bit digest value calculated by using the following Digest: A SHA-256 bit digest value calculated by using the following
formula ("|" denotes concatenation). The resulting value is not formula ("|" denotes concatenation). The resulting value is not
truncated and the entire 32 byte result is to used in the truncated, and the entire 32 byte result is to be used in the
resulting DS record and related calculations. resulting DS record and related calculations.
digest = SHA_256(DNSKEY owner name | DNSKEY RDATA) digest = SHA_256(DNSKEY owner name | DNSKEY RDATA)
where DNSKEY RDATA is defined by [RFC4034] as: where DNSKEY RDATA is defined by [RFC4034] as:
DNSKEY RDATA = Flags | Protocol | Algorithm | Public Key DNSKEY RDATA = Flags | Protocol | Algorithm | Public Key
The Key Tag field and Algorithm fields remain unchanged by this The Key Tag field and Algorithm fields remain unchanged by this
document and are specified in the [RFC4034] specification. document and are specified in the [RFC4034] specification.
2.2. DS Record with SHA-256 Wire Format 2.2. DS Record with SHA-256 Wire Format
The resulting on-the-wire format for the resulting DS record will be The resulting on-the-wire format for the resulting DS record will be
[XXX: IANA assignment should replace the 2 below]: as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Tag | Algorithm | DigestType=2 | | Key Tag | Algorithm | DigestType=2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ / / /
/ Digest (length for SHA-256 is 32 bytes) / / Digest (length for SHA-256 is 32 bytes) /
/ / / /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
skipping to change at page 4, line 33 skipping to change at page 3, line 38
dskey.example.com. 86400 IN DNSKEY 256 3 5 ( AQOeiiR0GOMYkDshWoSKz9Xz dskey.example.com. 86400 IN DNSKEY 256 3 5 ( AQOeiiR0GOMYkDshWoSKz9Xz
fwJr1AYtsmx3TGkJaNXVbfi/ fwJr1AYtsmx3TGkJaNXVbfi/
2pHm822aJ5iI9BMzNXxeYCmZ 2pHm822aJ5iI9BMzNXxeYCmZ
DRD99WYwYqUSdjMmmAphXdvx DRD99WYwYqUSdjMmmAphXdvx
egXd/M5+X7OrzKBaMbCVdFLU egXd/M5+X7OrzKBaMbCVdFLU
Uh6DhweJBjEVv5f2wwjM9Xzc Uh6DhweJBjEVv5f2wwjM9Xzc
nOf+EPbtG9DMBmADjFDc2w/r nOf+EPbtG9DMBmADjFDc2w/r
ljwvFw== ljwvFw==
) ; key id = 60485 ) ; key id = 60485
The resulting DS record covering the above DNSKEY record using a SHA- The resulting DS record covering the above DNSKEY record using a
256 digest: [RFC Editor: please replace XXX with the assigned digest SHA-256 digest:
type (likely 2):]
dskey.example.com. 86400 IN DS 60485 5 XXX ( D4B7D520E7BB5F0F67674A0C dskey.example.com. 86400 IN DS 60485 5 2 ( D4B7D520E7BB5F0F67674A0C
CEB1E3E0614B93C4F9E99B83 CEB1E3E0614B93C4F9E99B83
83F6A1E4469DA50A ) 83F6A1E4469DA50A )
3. Implementation Requirements 3. Implementation Requirements
Implementations MUST support the use of the SHA-256 algorithm in DS Implementations MUST support the use of the SHA-256 algorithm in DS
RRs. Validator implementations SHOULD ignore DS RRs containing SHA-1 RRs. Validator implementations SHOULD ignore DS RRs containing SHA-1
digests if DS RRs with SHA-256 digests are present in the DS RRset. digests if DS RRs with SHA-256 digests are present in the DS RRset.
4. Deployment Considerations 4. Deployment Considerations
If a validator does not support the SHA-256 digest type and no other If a validator does not support the SHA-256 digest type and no other
DS RR exists in a zone's DS RRset with a supported digest type, then DS RR exists in a zone's DS RRset with a supported digest type, then
the validator has no supported authentication path leading from the the validator has no supported authentication path leading from the
parent to the child. The resolver should treat this case as it would 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 the case of an authenticated NSEC RRset proving that no DS RRset
exists, as described in [RFC4035], section 5.2. exists, as described in [RFC4035], Section 5.2.
Because zone administrators can not control the deployment speed of Because zone administrators can not control the deployment speed of
support for SHA-256 in validators that may be referencing any of support for SHA-256 in validators that may be referencing any of
their zones, zone operators should consider deploying both SHA-1 and their zones, zone operators should consider deploying both SHA-1 and
SHA-256 based DS records. This should be done for every DNSKEY for SHA-256 based DS records. This should be done for every DNSKEY for
which DS records are being generated. Whether to make use of both which DS records are being generated. Whether to make use of both
digest types and for how long is a policy decision that extends digest types and for how long is a policy decision that extends
beyond the scope of this document. beyond the scope of this document.
5. IANA Considerations 5. IANA Considerations
Only one IANA action is required by this document: Only one IANA action is required by this document:
The Digest Type to be used for supporting SHA-256 within DS records The Digest Type to be used for supporting SHA-256 within DS records
needs to be assigned by IANA. This document requests that the Digest has been assigned by IANA.
Type value of 2 be assigned to the SHA-256 digest algorithm.
At the time of this writing, the current digest types assigned for At the time of this writing, the current digest types assigned for
use in DS records are as follows: use in DS records are as follows:
VALUE Digest Type Status VALUE Digest Type Status
0 Reserved - 0 Reserved -
1 SHA-1 MANDATORY 1 SHA-1 MANDATORY
2 SHA-256 MANDATORY 2 SHA-256 MANDATORY
3-255 Unassigned - 3-255 Unassigned -
6. Security Considerations 6. Security Considerations
6.1. Potential Digest Type Downgrade Attacks 6.1. Potential Digest Type Downgrade Attacks
A downgrade attack from a stronger digest type to a weaker one is A downgrade attack from a stronger digest type to a weaker one is
possible if all of the following are true: possible if all of the following are true:
o A zone includes multiple DS records for a given child's DNSKEY, o A zone includes multiple DS records for a given child's DNSKEY,
each of which use a different digest type. each of which uses a different digest type.
o A validator accepts a weaker digest even if a stronger one is o A validator accepts a weaker digest even if a stronger one is
present but invalid. present but invalid.
For example, if the following conditions are all true: For example, if the following conditions are all true:
o Both SHA-1 and SHA-256 based digests are published in DS records o Both SHA-1 and SHA-256 based digests are published in DS records
within a parent zone for a given child zone's DNSKEY. within a parent zone for a given child zone's DNSKEY.
o The DS record with the SHA-1 digest matches the digest computed o The DS record with the SHA-1 digest matches the digest computed
using the child zone's DNSKEY. using the child zone's DNSKEY.
o The DS record with the SHA-256 digest fails to match the digest o The DS record with the SHA-256 digest fails to match the digest
computed using the child zone's DNSKEY. computed using the child zone's DNSKEY.
Then if the validator accepts the above situation as secure then this Then, if the validator accepts the above situation as secure, then
can be used as a downgrade attack since the stronger SHA-256 digest this can be used as a downgrade attack since the stronger SHA-256
is ignored. digest is ignored.
6.2. SHA-1 vs SHA-256 Considerations for DS Records 6.2. SHA-1 vs. SHA-256 Considerations for DS Records
Users of DNSSEC are encouraged to deploy SHA-256 as soon as software Users of DNSSEC are encouraged to deploy SHA-256 as soon as software
implementations allow for it. SHA-256 is widely believed to be more implementations allow for it. SHA-256 is widely believed to be more
resilient to attack than SHA-1, and confidence in SHA-1's strength is resilient to attack than SHA-1, and confidence in SHA-1's strength is
being eroded by recently-announced attacks. Regardless of whether or being eroded by recently announced attacks. Regardless of whether
not the attacks on SHA-1 will affect DNSSEC, it is believed (at the the attacks on SHA-1 will affect DNSSEC, it is believed (at the time
time of this writing) that SHA-256 is the better choice for use in DS of this writing) that SHA-256 is the better choice for use in DS
records. records.
At the time of this publication, the SHA-256 digest algorithm is At the time of this publication, the SHA-256 digest algorithm is
considered sufficiently strong for the immediate future. It is also considered sufficiently strong for the immediate future. It is also
considered sufficient for use in DNSSEC DS RRs for the immediate considered sufficient for use in DNSSEC DS RRs for the immediate
future. However, future published attacks may weaken the usability future. However, future published attacks may weaken the usability
of this algorithm within the DS RRs. It is beyond the scope of this of this algorithm within the DS RRs. It is beyond the scope of this
document to speculate extensively on the cryptographic strength of document to speculate extensively on the cryptographic strength of
the SHA-256 digest algorithm. the SHA-256 digest algorithm.
Likewise, it is also beyond the scope of this document to specify Likewise, it is also beyond the scope of this document to specify
whether or for how long SHA-1 based DS records should be whether or for how long SHA-1 based DS records should be
simultaneously published alongside SHA-256 based DS records. simultaneously published alongside SHA-256 based DS records.
7. Acknowledgments 7. Acknowledgements
This document is a minor extension to the existing DNSSEC documents This document is a minor extension to the existing DNSSEC documents
and those authors are gratefully appreciated for the hard work that and those authors are gratefully appreciated for the hard work that
went into the base documents. went into the base documents.
The following people contributed to portions of this document in some The following people contributed to portions of this document in some
fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Paul Hoffman, fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Paul Hoffman,
Olaf M. Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam Olaf M. Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam
Weiler. Weiler.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements", RFC
RFC 4033, March 2005. 4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions", Rose, "Resource Records for the DNS Security
RFC 4034, March 2005. Extensions", RFC 4034, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005. Extensions", RFC 4035, March 2005.
[SHA256] National Institute of Standards and Technology, "Secure [SHA256] National Institute of Standards and Technology, "Secure
Hash Algorithm. NIST FIPS 180-2", August 2002. Hash Algorithm. NIST FIPS 180-2", August 2002.
8.2. Informative References 8.2. Informative References
[SHA256CODE] [SHA256CODE] Eastlake, D., "US Secure Hash Algorithms (SHA)", Work in
Eastlake, D., "US Secure Hash Algorithms (SHA)", Progress.
June 2005.
Author's Address Author's Address
Wes Hardaker Wes Hardaker
Sparta Sparta
P.O. Box 382 P.O. Box 382
Davis, CA 95617 Davis, CA 95617
US USA
Email: hardaker@tislabs.com EMail: hardaker@tislabs.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 9, line 29 skipping to change at page 7, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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Disclaimer of Validity Acknowledgement
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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