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DNS Extensions working group J. Jansen DNS Extensions working group J. Jansen
Internet-Draft NLnet Labs Internet-Draft NLnet Labs
Expires: August 19, 2008 February 16, 2008 Intended status: Standards Track October 23, 2008
Expires: April 26, 2009
Use of SHA-2 algorithms with RSA in DNSKEY and RRSIG Resource Records Use of SHA-2 algorithms with RSA in DNSKEY and RRSIG Resource Records
for DNSSEC for DNSSEC
draft-ietf-dnsext-dnssec-rsasha256-03 draft-ietf-dnsext-dnssec-rsasha256-06
Status of this Memo Status of this Memo
@ -33,11 +34,7 @@ Status of this Memo
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 19, 2008. This Internet-Draft will expire on April 26, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract Abstract
@ -52,9 +49,12 @@ Abstract
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Table of Contents Table of Contents
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2.2. RSA/SHA-512 DNSKEY Resource Records . . . . . . . . . . . . 3 2.2. RSA/SHA-512 DNSKEY Resource Records . . . . . . . . . . . . 3
3. RRSIG Resource Records . . . . . . . . . . . . . . . . . . . . 4 3. RRSIG Resource Records . . . . . . . . . . . . . . . . . . . . 4
3.1. RSA/SHA-256 RRSIG Resource Records . . . . . . . . . . . . 4 3.1. RSA/SHA-256 RRSIG Resource Records . . . . . . . . . . . . 4
3.2. RSA/SHA-512 RRSIG Resource Records . . . . . . . . . . . . 4 3.2. RSA/SHA-512 RRSIG Resource Records . . . . . . . . . . . . 5
4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5 4. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5
4.1. Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Signature Sizes . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Signature Sizes . . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Considerations . . . . . . . . . . . . . . . . . 5 5. Implementation Considerations . . . . . . . . . . . . . . . . . 5
5.1. Support for SHA-2 signatures . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7.1. SHA-1 versus SHA-2 Considerations for RRSIG Resource 7.1. SHA-1 versus SHA-2 Considerations for RRSIG Resource
@ -107,19 +108,19 @@ Table of Contents
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1. Introduction 1. Introduction
The Domain Name System (DNS) is the global hierarchical distributed The Domain Name System (DNS) is the global hierarchical distributed
database for Internet Addressing. The DNS has been extended to use database for Internet Naming. The DNS has been extended to use
cryptographic keys and digital signatures for the verification of the cryptographic keys and digital signatures for the verification of the
integrity of its data. RFC 4033 [1], RFC 4034 [2], and RFC 4035 [3] authenticity and integrity of its data. RFC 4033 [RFC4033], RFC 4034
describe these DNS Security Extensions, called DNSSEC. [RFC4034], and RFC 4035 [RFC4035] describe these DNS Security
Extensions, called DNSSEC.
RFC 4034 describes how to store DNSKEY and RRSIG resource records, RFC 4034 describes how to store DNSKEY and RRSIG resource records,
and specifies a list of cryptographic algorithms to use. This and specifies a list of cryptographic algorithms to use. This
@ -127,8 +128,8 @@ Internet-Draft DNSSEC RSA/SHA-2 February 2008
SHA-512, and specifies how to store DNSKEY data and how to produce SHA-512, and specifies how to store DNSKEY data and how to produce
RRSIG resource records with these hash algorithms. RRSIG resource records with these hash algorithms.
Familiarity with DNSSEC, RSA [7] and the SHA-2 [5] family of Familiarity with DNSSEC, RSA and the SHA-2 [FIPS.180-2.2002] family
algorithms is assumed in this document. of algorithms is assumed in this document.
To refer to both SHA-256 and SHA-512, this document will use the name 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 SHA-2. This is done to improve readability. When a part of text is
@ -139,66 +140,73 @@ Internet-Draft DNSSEC RSA/SHA-2 February 2008
2. DNSKEY Resource Records 2. DNSKEY Resource Records
The format of the DNSKEY RR can be found in RFC 4034 [2] and RFC 3110 The format of the DNSKEY RR can be found in RFC 4034 [RFC4034], RFC
[6]. 3110 [RFC3110] describes the use of RSA/SHA-1 for DNSSEC signatures.
2.1. RSA/SHA-256 DNSKEY Resource Records 2.1. RSA/SHA-256 DNSKEY Resource Records
RSA public keys for use with RSA/SHA-256 are stored in DNSKEY RSA public keys for use with RSA/SHA-256 are stored in DNSKEY
resource records (RRs) with the algorithm number {TBA1}. resource records (RRs) with the algorithm number {TBA1}.
For use with NSEC3, the algorithm number of RSA/SHA-256 will be For use with NSEC3 [RFC5155], the algorithm number for RSA/SHA-256
{TBA2}. will be {TBA2}. The use of a different algorithm number to
differentiate between the use of NSEC and NSEC3 is in keeping with
the approach adopted in RFC5155.
The key size for RSA/SHA-256 keys MUST NOT be less than 512 bits, and For interoperability, as in RFC 3110 [RFC3110], the key size of RSA/
MUST NOT be more than 4096 bits. SHA-256 keys MUST NOT be less than 512 bits, and MUST NOT be more
than 4096 bits.
2.2. RSA/SHA-512 DNSKEY Resource Records 2.2. RSA/SHA-512 DNSKEY Resource Records
RSA public keys for use with RSA/SHA-512 are stored in DNSKEY RSA public keys for use with RSA/SHA-512 are stored in DNSKEY
resource records (RRs) with the algorithm number {TBA3}. resource records (RRs) with the algorithm number {TBA3}.
For use with NSEC3, the algorithm number of RSA/SHA-512 will be
{TBA4}.
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The key size for RSA/SHA-512 keys MUST NOT be less than 1024 bits, For use with NSEC3, the algorithm number for RSA/SHA-512 will be
and MUST NOT be more than 4096 bits. {TBA4}. The use of a different algorithm number to differentiate
between the use of NSEC and NSEC3 is in keeping with the approach
adopted in RFC5155.
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 3. RRSIG Resource Records
The value of the signature field in the RRSIG RR follow the RSASSA- The value of the signature field in the RRSIG RR follows the RSASSA-
PKCS1-v1_5 signature scheme, and is calculated as follows. The PKCS1-v1_5 signature scheme, and is calculated as follows. The
values for the RDATA fields that precede the signature data are values for the RDATA fields that precede the signature data are
specified in RFC 4034 [2]. specified in RFC 4034 [RFC4034].
hash = SHA-XXX(data) hash = SHA-XXX(data)
Where XXX is either 256 or 512, depending on the algorithm used. Here XXX is either 256 or 512, depending on the algorithm used, as
specified in FIPS PUB 180-2 [FIPS.180-2.2002], 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) signature = ( 00 | 01 | FF* | 00 | prefix | hash ) ** e (mod n)
Where SHA-XXX is the message digest algorithm as specified in FIPS Here "|" is concatenation, "00", "01", "FF" and "00" are fixed octets
PUB 180-2 [5], "|" is concatenation, "00", "01", "FF" and "00" are of corresponding hexadecimal value, "e" is the private exponent of
fixed octets of corresponding hexadecimal value, "e" is the private the signing RSA key, and "n" is the public modulus of the signing
exponent of the signing RSA key, and "n" is the public modulus of the key. The FF octet MUST be repeated the exact number of times so that
signing key. The FF octet MUST be repeated the maximum number of the total length of the concatenated term in parentheses equals the
times so that the total length of the signature equals the length of length of the modulus of the signer's public key ("n").
the modulus of the signer's public key ("n"). "data" is the data of
the resource record set that is signed, as specified in RFC 4034 [2].
The "prefix" is intended to make the use of standard cryptographic The "prefix" is intended to make the use of standard cryptographic
libraries easier. These specifications are taken directly from the libraries easier. These specifications are taken directly from the
specification of EMSA-PKCS1-v1_5 encoding in PKCS #1 v2.1 section 9.2 specifications of RSASSA-PKCS1-v1_5 in PKCS #1 v2.1 section 8.2
[4]. The prefixes for the different algorithms are specified below. [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 3.1. RSA/SHA-256 RRSIG Resource Records
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{TBA2} for use with NSEC3. {TBA2} for use with NSEC3.
The prefix is the ASN.1 BER SHA-256 algorithm designator prefix as The prefix is the ASN.1 BER SHA-256 algorithm designator prefix as
specified in PKCS #1 v2.1 [4]: specified in PKCS #1 v2.1 [RFC3447]:
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hex 30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20 hex 30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20
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records (RRs) with algorithm number {TBA3} for use with NSEC, or records (RRs) with algorithm number {TBA3} for use with NSEC, or
{TBA4} for use with NSEC3. {TBA4} for use with NSEC3.
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The prefix is the ASN.1 BER SHA-512 algorithm designator prefix as The prefix is the ASN.1 BER SHA-512 algorithm designator prefix as
specified in PKCS #1 v2.1 [4]: 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 hex 30 51 30 0d 06 09 60 86 48 01 65 03 04 02 03 05 00 04 40
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4.1. Key Sizes 4.1. Key Sizes
Apart from prohibiting RSA/SHA-512 signatures smaller than 1024 Apart from the restrictions specified in section 2, this document
bytes, this document will not specify what size of keys to use. That will not specify what size of keys to use. That is an operational
is more an operational issue and depends largely on the environment issue and depends largely on the environment and intended use. A
and intended use. Some good starting points might be DNSSEC good starting point for more information would be NIST SP 800-57
Operational Practises [9], section 3.5, and NIST SP 800-57 Part 1 [NIST800-57].
[10] and Part 3 [11].
4.2. Signature Sizes 4.2. Signature Sizes
In this family of signing algorithms, the size of signatures is 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 related to the size of the key, and not the hashing algorithm used in
the signing process. Therefore, RRSIG resource records produced with the signing process. Therefore, RRSIG resource records produced with
RSA/SHA256 or RSA/SHA512 shall have the same size as those produced RSA/SHA256 or RSA/SHA512 will have the same size as those produced
with RSA/SHA1, if the keys have the same length. with RSA/SHA1, if the keys have the same length.
5. Implementation Considerations 5. Implementation Considerations
5.1. Support for SHA-2 signatures
DNSSEC aware implementations SHOULD be able to support RRSIG resource DNSSEC aware implementations SHOULD be able to support RRSIG resource
records with the RSA/SHA-2 algorithms. records with the RSA/SHA-2 algorithms.
If both RSA/SHA-2 and RSA/SHA-1 RRSIG resource records are available
for a certain RRset, with a secure path to their keys, the validator
SHOULD ignore the SHA-1 signature. If the RSA/SHA-2 signature does
not verify the data, and the RSA/SHA-1 signature does, the validator
SHOULD mark the data with the security status from the RSA/SHA-2
signature.
6. IANA Considerations 6. IANA Considerations
IANA has not yet assigned an algorithm number for RSA/SHA-256 and IANA has assigned DNS Security Algorithm Numbers {TBA1} for RSA/
RSA/SHA-512. SHA-256 with NSEC, {TBA2} for RSA/SHA-256 with NSEC3, {TBA3} for RSA/
SHA-512 with NSEC, and {TBA4} for RSA/SHA-512 with NSEC3.
The algorithm list from RFC 4034 Appendix A.1 [2] is extended with The algorithm list from RFC 4034 Appendix A.1 [RFC4034] is extended
the following entries:
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with the following entries:
Zone Zone
Value Algorithm [Mnemonic] Signing References Status Value Algorithm [Mnemonic] Signing References
----- ----------- ----------- ------- ----------- -------- {TBA1} RSA/SHA-256 RSASHA256 y {this memo}
{TBA1} RSA/SHA-256 RSASHA256 y {this memo} OPTIONAL {TBA2} RSA/SHA-256-NSEC3 RSASHA256NSEC3 y {this memo}
{TBA2} RSA/SHA-256-NSEC3 RSASHA256NSEC3 y {this memo} OPTIONAL {TBA3} RSA/SHA-512 RSASHA512 y {this memo}
{TBA3} RSA/SHA-512 RSASHA512 y {this memo} OPTIONAL {TBA4} RSA/SHA-512-NSEC3 RSASHA512NSEC3 y {this memo}
{TBA4} RSA/SHA-512-NSEC3 RSASHA512NSEC3 y {this memo} OPTIONAL
7. Security Considerations 7. Security Considerations
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7.2. Signature Type Downgrade Attacks 7.2. Signature Type Downgrade Attacks
Since each RRset MUST be signed with each algorithm present in the Since each RRSet MUST be signed with each algorithm present in the
DNSKEY RRset at the zone apex (see [3] Section 2.2), a malicious DNSKEY RRSet at the zone apex (see [RFC4035] Section 2.2), a
party cannot filter out the RSA/SHA-2 RRSIG, and force the validator malicious party cannot filter out the RSA/SHA-2 RRSIG, and force the
to use the RSA/SHA-1 signature if both are present in the zone. validator to use the RSA/SHA-1 signature if both are present in the
Together with the implementation considerations from Section 5 of zone. This should provide resilience against algorithm downgrade
this document, this provides resilience against algorithm downgrade
attacks, if the validator supports RSA/SHA-2. attacks, if the validator supports RSA/SHA-2.
8. Acknowledgments 8. Acknowledgments
This document is a minor extension to RFC 4034 [2]. Also, we try to This document is a minor extension to RFC 4034 [RFC4034]. Also, we
follow the documents RFC 3110 [6] and RFC 4509 [8] for consistency. try to follow the documents RFC 3110 [RFC3110] and RFC 4509 [RFC4509]
The authors of and contributors to these documents are gratefully for consistency. The authors of and contributors to these documents
acknowledged for their hard work. are gratefully acknowledged for their hard work.
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The following people provided additional feedback and text: Jaap The following people provided additional feedback and text: Jaap
Akkerhuis, Roy Arends, Rob Austein, Francis Dupont, Miek Gieben,
Alfred Hoenes, Paul Hoffman, Peter Koch, Michael St. Johns, Scott
Rose and Wouter Wijngaards.
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Akkerhuis, Roy Arends, Rob Austein, Miek Gieben, Alfred Hoenes,
Michael St. Johns, Scott Rose and Wouter Wijngaards.
9. References 9. References
9.1. Normative References 9.1. Normative References
[1] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [FIPS.180-2.2002]
"DNS Security Introduction and Requirements", RFC 4033, National Institute of Standards and Technology, "Secure
March 2005. Hash Standard", FIPS PUB 180-2, August 2002.
[2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [RFC3110] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain
"Resource Records for the DNS Security Extensions", RFC 4034, Name System (DNS)", RFC 3110, May 2001.
March 2005.
[3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
"Protocol Modifications for the DNS Security Extensions", Rose, "DNS Security Introduction and Requirements",
RFC 4035, March 2005. RFC 4033, March 2005.
[4] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
(PKCS) #1: RSA Cryptography Specifications Version 2.1", Rose, "Resource Records for the DNS Security Extensions",
RFC 3447, February 2003. RFC 4034, March 2005.
[5] National Institute of Standards and Technology, "Secure Hash [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Standard", FIPS PUB 180-2, August 2002. Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[6] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name
System (DNS)", RFC 3110, May 2001.
9.2. Informative References 9.2. Informative References
[7] Schneier, B., "Applied Cryptography Second Edition: protocols, [NIST800-57]
algorithms, and source code in C", Wiley and Sons , ISBN 0-471- Barker, E., Barker, W., Burr, W., Polk, W., and M. Smid,
11709-9, 1996. "Recommendations for Key Management", NIST SP 800-57,
[8] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer (DS)
Resource Records (RRs)", RFC 4509, May 2006.
[9] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
RFC 4641, September 2006.
[10] Barker, E., Barker, W., Burr, W., Polk, W., and M. Smid,
"Recommendations for Key Management Part 1: General", NIST
SP 800-57 Part 1, March 2007.
[11] Barker, E., Barker, W., Burr, W., Jones, A., Polk, W., Smid,
M., and S. Rose, "Recommendations for Key Management Part 3:
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Application-Specific Key Guidance", NIST SP 800-57 Part 3,
March 2007. March 2007.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
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.
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Author's Address Author's Address
@ -444,9 +440,13 @@ Author's Address
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Full Copyright Statement Full Copyright Statement
@ -491,14 +491,14 @@ Intellectual Property
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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