DNS Extensions working group                                   J. Jansen
Internet-Draft                                                NLnet Labs
Intended status: Standards Track                          March 23,                          April 24, 2009
Expires: September 24, October 26, 2009

 Use of SHA-2 algorithms with RSA in DNSKEY and RRSIG Resource Records
                               for DNSSEC
                 draft-ietf-dnsext-dnssec-rsasha256-12
                 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-
   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 24, 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
   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
       5.2.1.  NSEC3 in Authoritative servers
   6.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
       5.2.2.  NSEC3 in Validators
     6.1.  RSA/SHA-256 Key and Signature  . . . . . . . . . . . . . .  6
     6.2.  RSA/SHA-512 Key and Signature  . . . . . . . . . . . . . .  6
   6.
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . . 6
   7.  8
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . . 6
     7.1.  8
     8.1.  SHA-1 versus SHA-2 Considerations for RRSIG Resource
           Records  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     7.2.  8
     8.2.  Signature Type Downgrade Attacks . . . . . . . . . . . . . 7
   8.  8
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . 7
   9.  9
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     9.1.  9
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 7
     9.2.  9
     10.2. Informative References . . . . . . . . . . . . . . . . . . 8  9
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 10

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.

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

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, aliases.

   A DNSSEC validator that implements RSA/SHA-2 MUST be able to validate
   both NSEC and support for NSEC3 denial of existence is
   implicitly signaled with support for one of the algorithms defined in
   this document.

5.2.1. NSEC3 in Authoritative servers [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.

5.2.2.  NSEC3 in Validators

   A DNSSEC validator that implements RSA/SHA-2 MUST be able to handle
   both NSEC

6.  Examples

6.1.  RSA/SHA-256 Key and NSEC3 [RFC5155] negative answers.  If 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 not set at 00:00 hours on January 1st, 2000, and
   the
   case, expiration date at 00:00 hours on January 1st, 2030, the validator MUST treat
   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 zone signed with RSA/SHA-256 or RSA/
   SHA-512 as signed private key with an unknown algorithm, the following values (in Base64):

   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 thus as insecure.

6.
   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}

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.

7.

8.  Security Considerations

7.1.

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.

7.2.

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.

8.

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.

9.

10.  References

9.1.

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.

9.2.

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
              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/