draft-ietf-dnsext-ds-sha256-02.txt   draft-ietf-dnsext-ds-sha256-03.txt 
Network Working Group W. Hardaker Network Working Group W. Hardaker
Internet-Draft Sparta Internet-Draft Sparta
Expires: June 12, 2006 December 9, 2005 Expires: July 10, 2006 January 6, 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-sha256-02.txt draft-ietf-dnsext-ds-sha256-03.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). 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 key signing DNSKEY key(s) in a
child zone. child zone.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Implementing the SHA-256 algorithm for DS record support . . . 3 2. Implementing the SHA-256 algorithm for DS record support . . . 3
2.1. DS record field values . . . . . . . . . . . . . . . . . . 3 2.1. DS record field values . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . 4
3. Implementation Requirements . . . . . . . . . . . . . . . . . . 4 3. Implementation Requirements . . . . . . . . . . . . . . . . . . 4
4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5 4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6.1. Potential Digest Type Downgrade Attacks . . . . . . . . . . 5
6.2. SHA-1 vs SHA-256 Considerations for DS Records . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 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 a child's Key Signing
Key (KSK) DNSKEY RR. The DS RRset is signed by at least one of the Key (KSK) DNSKEY RR. The DS RRset is signed by at least one of the
parent zone's private zone data signing keys for each algorithm in parent zone's private zone data signing keys for each algorithm in
use by the parent. Each signature is published in an RRSIG resource use by the parent. Each signature is published in an RRSIG resource
record, owned by the same domain as the DS RRset and with a type record, owned by the same domain as the DS RRset and with a type
covered of DS. covered of DS.
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/ Digest (length for SHA-256 is 32 bytes) / / Digest (length for SHA-256 is 32 bytes) /
/ / / /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
2.3. Example DS Record Using SHA-256 2.3. Example DS Record Using SHA-256
The following is an example DNSKEY and matching DS record. This The following is an example DNSKEY and matching DS record. This
DNSKEY record comes from the example DNSKEY/DS records found in DNSKEY record comes from the example DNSKEY/DS records found in
section 5.4 of [RFC4034]. section 5.4 of [RFC4034].
The DNSKEY record:: The DNSKEY record:
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
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256 digest: [RFC Editor: please replace XXX with the assigned digest 256 digest: [RFC Editor: please replace XXX with the assigned digest
type (likely 2):] type (likely 2):]
dskey.example.com. 86400 IN DS 60485 5 XXX ( D4B7D520E7BB5F0F67674A0C dskey.example.com. 86400 IN DS 60485 5 XXX ( 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. RRs. Validator implementations SHOULD ignore DS RRs containing SHA-1
digests if DS RRs with SHA-256 digests are present in the DS RRset.
Validator implementations MUST, by default, ignore DS RRs containing
SHA-1 digests if DS RRs with SHA-256 digests are present in the DS
RRset. This behavior SHOULD be the default. Validator
implementations MAY provide configuration settings that allow network
operators to specify preference policy when validating multiple DS
records containing different digest types.
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.
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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
A downgrade attack from a stronger digest type to a weaker one is
possible if all of the following are true:
o A zone includes multiple DS records for a given child's DNSKEY,
each of which use a different digest type.
o A validator accepts a weaker digest even if a stronger one is
present but invalid.
For example, if the following conditions are all true:
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.
o The DS record with the SHA-1 digest matches the digest computed
using the child zone's DNSKEY.
o The DS record with the SHA-256 digest fails to match the signature
computed using the child zone's DNSKEY
Then if the validator accepts the above situation as secure then this
can be used as a downgrade attack since the stronger SHA-256 digest
is ignored.
6.2. SHA-1 vs SHA-256 Considerations for DS Records
Because of the weaknesses recently discovered within the SHA-1 Because of the weaknesses recently discovered within the SHA-1
algorithm, users of DNSSEC are encouraged to deploy the use of SHA- algorithm, users of DNSSEC are encouraged to deploy the use of SHA-
256 as soon as the software implementations in use allow for it. 256 as soon as the software implementations in use allow for it.
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, of course, weaken the future. However, future published attacks may weaken the usability
usability of this algorithm within the DS RRs. It is beyond the of this algorithm within the DS RRs. It is beyond the scope of this
scope of this document to speculate extensively on the cryptographic document to speculate extensively on the cryptographic strength of
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. Acknowledgments
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, Olaf M. fashion: Mark Andrews, Roy Arends, Olafur Gudmundsson, Olaf M.
Kolkman, Edward Lewis, Scott Rose, Sam Weiler. Kolkman, Edward Lewis, Scott Rose, Stuart E. Schechter, Sam Weiler.
8. References 8. References
8.1. Normative References 8.1. Normative References
[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 4033, March 2005. RFC 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.
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[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]
Motorola Labs, "US Secure Hash Algorithms (SHA)",
June 2005.
Author's Address Author's Address
Wes Hardaker Wes Hardaker
Sparta Sparta
P.O. Box 382 P.O. Box 382
Davis 95617 Davis 95617
US US
Email: hardaker@tislabs.com Email: hardaker@tislabs.com
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This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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