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bind9/doc/draft/draft-ietf-dnsext-dnssec-rsasha256-13.txt
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DNS Extensions working group J. Jansen
Internet-Draft NLnet Labs
Intended status: Standards Track April 24, 2009
Expires: October 26, 2009
Use of SHA-2 algorithms with RSA in DNSKEY and RRSIG Resource Records
for DNSSEC
draft-ietf-dnsext-dnssec-rsasha256-13
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-
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and may be updated, replaced, or obsoleted by other documents at any
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http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 26, 2009.
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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
This document describes how to produce RSA/SHA-256 and RSA/SHA-512
DNSKEY and RRSIG resource records for use in the Domain Name System
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Security Extensions (DNSSEC, RFC 4033, RFC 4034, and RFC 4035).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. DNSKEY Resource Records . . . . . . . . . . . . . . . . . . . 3
2.1. RSA/SHA-256 DNSKEY Resource Records . . . . . . . . . . . 3
2.2. RSA/SHA-512 DNSKEY Resource Records . . . . . . . . . . . 4
3. RRSIG Resource Records . . . . . . . . . . . . . . . . . . . . 4
3.1. RSA/SHA-256 RRSIG Resource Records . . . . . . . . . . . . 4
3.2. RSA/SHA-512 RRSIG Resource Records . . . . . . . . . . . . 5
4. Deployment Considerations . . . . . . . . . . . . . . . . . . 5
4.1. Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Signature Sizes . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Considerations . . . . . . . . . . . . . . . . 5
5.1. Support for SHA-2 signatures . . . . . . . . . . . . . . . 5
5.2. Support for NSEC3 Denial of Existence . . . . . . . . . . 5
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. RSA/SHA-256 Key and Signature . . . . . . . . . . . . . . 6
6.2. RSA/SHA-512 Key and Signature . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8.1. SHA-1 versus SHA-2 Considerations for RRSIG Resource
Records . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.2. Signature Type Downgrade Attacks . . . . . . . . . . . . . 8
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
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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 algorithms RSA/SHA-256 and RSA/
SHA-512, and specifies how to store DNSKEY data and how to produce
RRSIG resource records with these hash algorithms.
Familiarity with DNSSEC, RSA and the SHA-2 [FIPS.180-3.2008] family
of algorithms is assumed in this document.
To refer to both SHA-256 and SHA-512, this document will use the name
SHA-2. This is done to improve readability. When a part of text is
specific for either SHA-256 or SHA-512, their specific names are
used. The same goes for RSA/SHA-256 and RSA/SHA-512, which will be
grouped using the name RSA/SHA-2.
The term "SHA-2" is not officially defined, but is usually used to
refer to the collection of the algorithms SHA-224, SHA-256, SHA-384
and SHA-512. Since SHA-224 and SHA-384 are not used in DNSSEC, SHA-2
will only refer to SHA-256 and SHA-512 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].
2. DNSKEY Resource Records
The format of the DNSKEY RR can be found in RFC 4034 [RFC4034]. RFC
3110 [RFC3110] describes the use of RSA/SHA-1 for DNSSEC signatures.
2.1. RSA/SHA-256 DNSKEY Resource Records
RSA public keys for use with RSA/SHA-256 are stored in DNSKEY
resource records (RRs) with the algorithm number {TBA1}.
For interoperability, as in RFC 3110 [RFC3110], the key size of RSA/
SHA-256 keys MUST NOT be less than 512 bits, and MUST NOT be more
than 4096 bits.
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2.2. RSA/SHA-512 DNSKEY Resource Records
RSA public keys for use with RSA/SHA-512 are stored in DNSKEY
resource records (RRs) with the algorithm number {TBA2}.
The key size of RSA/SHA-512 keys MUST NOT be less than 1024 bits, and
MUST NOT be more than 4096 bits.
3. RRSIG Resource Records
The value of the signature field in the RRSIG RR follows the RSASSA-
PKCS1-v1_5 signature scheme, and is calculated as follows. The
values for the RDATA fields that precede the signature data are
specified in RFC 4034 [RFC4034].
hash = SHA-XXX(data)
Here XXX is either 256 or 512, depending on the algorithm used, as
specified in FIPS PUB 180-3 [FIPS.180-3.2008], and "data" is the wire
format data of the resource record set that is signed, as specified
in RFC 4034 [RFC4034].
signature = ( 00 | 01 | FF* | 00 | prefix | hash ) ** e (mod n)
Here "|" is concatenation, "00", "01", "FF" and "00" are fixed octets
of corresponding hexadecimal value, "e" is the private exponent of
the signing RSA key, and "n" is the public modulus of the signing
key. The FF octet MUST be repeated the exact number of times so that
the total length of the concatenated term in parentheses equals the
length of the modulus of the signer's public key ("n").
The "prefix" is intended to make the use of standard cryptographic
libraries easier. These specifications are taken directly from the
specifications of RSASSA-PKCS1-v1_5 in PKCS #1 v2.1 section 8.2
[RFC3447], and EMSA-PKCS1-v1_5 encoding in PKCS #1 v2.1 section 9.2
[RFC3447]. The prefixes for the different algorithms are specified
below.
3.1. RSA/SHA-256 RRSIG Resource Records
RSA/SHA-256 signatures are stored in the DNS using RRSIG resource
records (RRs) with algorithm number {TBA1}.
The prefix is the ASN.1 DER SHA-256 algorithm designator prefix as
specified in PKCS #1 v2.1 [RFC3447]:
hex 30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20
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3.2. RSA/SHA-512 RRSIG Resource Records
RSA/SHA-512 signatures are stored in the DNS using RRSIG resource
records (RRs) with algorithm number {TBA2}.
The prefix is the ASN.1 DER SHA-512 algorithm designator prefix as
specified in PKCS #1 v2.1 [RFC3447]:
hex 30 51 30 0d 06 09 60 86 48 01 65 03 04 02 03 05 00 04 40
4. Deployment Considerations
4.1. Key Sizes
Apart from the restrictions in section 2, this document will not
specify what size of keys to use. That is an operational issue and
depends largely on the environment and intended use. A good starting
point for more information would be NIST SP 800-57 [NIST800-57].
4.2. Signature Sizes
In this family of signing algorithms, the size of signatures is
related to the size of the key, and not the hashing algorithm used in
the signing process. Therefore, RRSIG resource records produced with
RSA/SHA-256 or RSA/SHA-512 will have the same size as those produced
with RSA/SHA-1, if the keys have the same length.
5. Implementation Considerations
5.1. Support for SHA-2 signatures
DNSSEC aware implementations SHOULD be able to support RRSIG and
DNSKEY resource records created with the RSA/SHA-2 algorithms as
defined in this document.
5.2. Support for NSEC3 Denial of Existence
RFC 5155 [RFC5155] defines new algorithm identifiers for existing
signing algorithms, to indicate that zones signed with these
algorithm identifiers can use NSEC3 as well as NSEC records to
provide denial of existence. That mechanism was chosen to protect
implementations predating RFC5155 from encountering resource records
they could not know about. This document does not define such
algorithm aliases.
A DNSSEC validator that implements RSA/SHA-2 MUST be able to validate
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both NSEC and NSEC3 [RFC5155] negative answers. An authoritative
server that does not implement NSEC3 MAY still serve zones that use
RSA/SHA-2 with NSEC denial of existence.
6. Examples
6.1. RSA/SHA-256 Key and Signature
Given a private key with the following values (in Base64):
Private-key-format: v1.2
Algorithm: 8 (RSASHA256)
Modulus: wVwaxrHF2CK64aYKRUibLiH30KpPuPBjel7E8ZydQW1HYWHfoGm
idzC2RnhwCC293hCzw+TFR2nqn8OVSY5t2Q==
PublicExponent: AQAB
PrivateExponent: UR44xX6zB3eaeyvTRzmskHADrPCmPWnr8dxsNwiDGHzrMKLN+i/
HAam+97HxIKVWNDH2ba9Mf1SA8xu9dcHZAQ==
Prime1: 4c8IvFu1AVXGWeFLLFh5vs7fbdzdC6U82fduE6KkSWk=
Prime2: 2zZpBE8ZXVnL74QjG4zINlDfH+EOEtjJJ3RtaYDugvE=
Exponent1: G2xAPFfK0KGxGANDVNxd1K1c9wOmmJ51mGbzKFFNMFk=
Exponent2: GYxP1Pa7CAwtHm8SAGX594qZVofOMhgd6YFCNyeVpKE=
Coefficient: icQdNRjlZGPmuJm2TIadubcO8X7V4y07aVhX464tx8Q=
The DNSKEY record for this key would be:
example.net. 3600 IN DNSKEY (256 3 8 AwEAAcFcGsaxxdgiuuGmCkVI
my4h99CqT7jwY3pexPGcnUFtR2Fh36BponcwtkZ4cAgtvd4Qs8P
kxUdp6p/DlUmObdk= );{id = 9033 (zsk), size = 512b}
With this key, sign the following RRSet, consisting of 1 A record:
www.example.net. 3600 IN A 123.123.123.123
If the inception date is set at 00:00 hours on January 1st, 2000, and
the expiration date at 00:00 hours on January 1st, 2030, the
following signature should be created:
www.example.net. 3600 IN RRSIG (A 8 3 3600 20300101000000
20000101000000 9033 example.net. KWgSIg3khRfyrHmtJU
5pzpsANyy27+HOZ6waMQ5kV690ljVmbHmGc8ULOfXw3aWmP0wJB
ND/TQhjCvrb3T9ffQ== );{id = 9033}
6.2. RSA/SHA-512 Key and Signature
Given a private key with the following values (in Base64):
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Private-key-format: v1.2
Algorithm: 9 (RSASHA512)
Modulus: 8Du9YHEwFNjO5iG9jrrNyKwRs5mAzJgXBrjbA49R/ESWJKw6eHH
XfZaxnP+gVhZBDmqwND/SFwrEkN5LyH3HZ+/d/ECW+vT8Lxprqf
haTfxQkV4OFjw/ikuTcBMoUIYfhO1NVPBcH1mWh34DWmu6eedzH
IbdeNZnIkWSv4muchs=
PublicExponent: AQAB
PrivateExponent: sRm5YLHQ2m2DCdDx55j7P+bqHdcaRroQr5nzi8pKjIkbjumRKV3
zmNhRFAa3cv9w8mnggIRUIzyC8LGQeLuRFjbv6uXDzoPX2O321j
PlTUOwCYMTVnbkZUem6c+7iRd2v5zNNe9uiXex6T8CDXyhQhqYb
8q2AajPrTlRzv6uW8E=
Prime1: +DPVg2OlfYqcNlm67T42608gjyqWFdVc0UtDDDBo+ABWavqp+Yk
Fb/z/Ig+iBE901Q8RWdqVLND3PtGwWipIyw==
Prime2: 98fQbOaWH3D/WFhnu47f1qOgaob/ss3FQ12QbUdRDpgfmdryHH7
j1UGR2Xs0aRPwBASXYhgtamXtxLorXIFh8Q==
Exponent1: j0UsbGlqr6sBPQZStnuBLBdCziFg/T1qFI4DJ9gR34YiXCJRV29
Wqiw6AalQdnh/EjVeaKWaEoKVFbfoukNKPQ==
Exponent2: 4YTy9ftVjd5p+f3UxEgBATnCatLebd6NeYfySRQM+YyJzp4RmNA
BC/t3BQv3IuBrpyyKoFTDGUEWjOSpTLPR8Q==
Coefficient: BpIAEwh5rlw9M8FpGHjpF5TxSdhCjnA8NT0tB+MB/k0msceyBbx
avjzJXTi/QPk9PIO8Wv6eCzMQEM0QDZO53Q==
The DNSKEY record for this key would be:
example.net. 3600 IN DNSKEY (256 3 9 AwEAAfA7vWBxMBTYzuYhvY66z
cisEbOZgMyYFwa42wOPUfxEliSsOnhx132WsZz/oFYWQQ5qsDQ/0
hcKxJDeS8h9x2fv3fxAlvr0/C8aa6n4Wk38UJFeDhY8P4pLk3ATK
FCGH4TtTVTwXB9Zlod+A1prunnncxyG3XjWZyJFkr+JrnIb
);{id = 28237 (zsk), size = 1024b}
With this key, sign the following RRSet, consisting of 1 A record:
www.example.net. 3600 IN A 123.123.123.123
If the inception date is set at 00:00 hours on January 1st, 2000, and
the expiration date at 00:00 hours on January 1st, 2030, the
following signature should be created:
www.example.net. 3600 IN RRSIG (A 9 3 3600 20300101000000
20000101000000 28237 example.net. mCanSdkQztEUOmslG
z7VvfkKPMp4ftz3K1PTf2jdla4vUu/tRE585xymurMB+wXhrFcK
dhm0egnPq8X/gmm0cmui/GQwFT5hmP5bL1ETuQsM3HOu3j9E3tq
4sFWIsUv3N6ohpYEbhj5jk0b/01EMUPM9y5rLzFHmYYujzKQwqu
M= );{id = 28237}
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7. IANA Considerations
This document updates the IANA registry "DNS SECURITY ALGORITHM
NUMBERS -- per [RFC4035] "
(http://www.iana.org/assignments/dns-sec-alg-numbers). The following
entries are added to the registry:
Zone Trans.
Value Description Mnemonic Signing Sec. References
{TBA1} RSA/SHA-256 RSASHA256 y * {this memo}
{TBA2} RSA/SHA-512 RSASHA512 y * {this memo}
* There has been no determination of standardization of the use of this
algorithm with Transaction Security.
8. Security Considerations
8.1. SHA-1 versus SHA-2 Considerations for RRSIG Resource Records
Users of DNSSEC are encouraged to deploy SHA-2 as soon as software
implementations allow for it. SHA-2 is widely believed to be more
resilient to attack than SHA-1, and confidence in SHA-1's strength is
being eroded by recently-announced attacks. Regardless of whether or
not the attacks on SHA-1 will affect DNSSEC, it is believed (at the
time of this writing) that SHA-2 is the better choice for use in
DNSSEC records.
SHA-2 is considered sufficiently strong for the immediate future, but
predictions about future development in cryptography and
cryptanalysis are beyond the scope of this document.
The signature scheme RSASSA-PKCS1-v1_5 is chosen to match the one
used for RSA/SHA-1 signatures. This should ease implementation of
the new hashing algorithms in DNSSEC software.
8.2. Signature Type Downgrade Attacks
Since each RRSet MUST be signed with each algorithm present in the
DNSKEY RRSet at the zone apex (see [RFC4035] Section 2.2), a
malicious party cannot filter out the RSA/SHA-2 RRSIG, and force the
validator to use the RSA/SHA-1 signature if both are present in the
zone. This should provide resilience against algorithm downgrade
attacks, if the validator supports RSA/SHA-2.
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9. Acknowledgments
This document is a minor extension to RFC 4034 [RFC4034]. Also, we
try to follow the documents RFC 3110 [RFC3110] and RFC 4509 [RFC4509]
for consistency. The authors of and contributors to these documents
are gratefully acknowledged for their hard work.
The following people provided additional feedback and text: Jaap
Akkerhuis, Mark Andrews, Roy Arends, Rob Austein, Francis Dupont,
Miek Gieben, Alfred Hoenes, Paul Hoffman, Peter Koch, Michael St.
Johns, Scott Rose and Wouter Wijngaards.
10. References
10.1. Normative References
[FIPS.180-3.2008]
National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-3, October 2008.
[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.
10.2. Informative References
[NIST800-57]
Barker, E., Barker, W., Burr, W., Polk, W., and M. Smid,
"Recommendations for Key Management", NIST SP 800-57,
March 2007.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
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Version 2.1", RFC 3447, February 2003.
[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.
Author's Address
Jelte Jansen
NLnet Labs
Kruislaan 419
Amsterdam 1098VA
NL
Email: jelte@NLnetLabs.nl
URI: http://www.nlnetlabs.nl/
Jansen Expires October 26, 2009 [Page 10]
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