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Network Working Group                                          J. JansenRequest for Comments: 5702                                    NLnet LabsCategory: Standards Track                                   October 2009Use of SHA-2 Algorithms with RSA inDNSKEY and RRSIG Resource Records for DNSSECAbstract   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 (RFC 4033,RFC 4034, andRFC 4035).Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the BSD License.Jansen                      Standards Track                     [Page 1]

RFC 5702                    DNSSEC RSA/SHA-2                October 2009Table of Contents1. Introduction ....................................................22. DNSKEY Resource Records .........................................32.1. RSA/SHA-256 DNSKEY Resource Records ........................32.2. RSA/SHA-512 DNSKEY Resource Records ........................33. RRSIG Resource Records ..........................................33.1. RSA/SHA-256 RRSIG Resource Records .........................43.2. RSA/SHA-512 RRSIG Resource Records .........................44. Deployment Considerations .......................................54.1. Key Sizes ..................................................54.2. Signature Sizes ............................................55. Implementation Considerations ...................................55.1. Support for SHA-2 Signatures ...............................55.2. Support for NSEC3 Denial of Existence ......................56. Examples ........................................................66.1. RSA/SHA-256 Key and Signature ..............................66.2. RSA/SHA-512 Key and Signature ..............................77. IANA Considerations .............................................88. Security Considerations .........................................8      8.1. SHA-1 versus SHA-2 Considerations for RRSIG           Resource Records ...........................................88.2. Signature Type Downgrade Attacks ...........................89. Acknowledgments .................................................910. References .....................................................910.1. Normative References ......................................910.2. Informative References ....................................91.  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.  [RFC4033], [RFC4034], and   [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.Jansen                      Standards Track                     [Page 2]

RFC 5702                    DNSSEC RSA/SHA-2                October 2009   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 [RFC4034].  [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 8.   For interoperability, as in [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 10.   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   [RFC4034].Jansen                      Standards Track                     [Page 3]

RFC 5702                    DNSSEC RSA/SHA-2                October 2009   hash = SHA-XXX(data)   Here XXX is either 256 or 512, depending on the algorithm used, as   specified in FIPS PUB 180-3; "data" is the wire format data of the   resource record set that is signed, as specified in [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 of   [RFC3447]), and EMSA-PKCS1-v1_5 encoding in PKCS #1 v2.1 (Section 9.2   of [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 8.   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 04 203.2.  RSA/SHA-512 RRSIG Resource Records   RSA/SHA-512 signatures are stored in the DNS using RRSIG resource   records (RRs) with algorithm number 10.   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 40Jansen                      Standards Track                     [Page 4]

RFC 5702                    DNSSEC RSA/SHA-2                October 20094.  Deployment Considerations4.1.  Key Sizes   Apart from the restrictions inSection 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 to 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 Considerations5.1.  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   [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   predatingRFC 5155 from encountering resource records about which   they could not know.  This document does not define such algorithm   aliases.   A DNSSEC validator that implements RSA/SHA-2 MUST be able to validate   negative answers in the form of both NSEC and NSEC3 with hash   algorithm 1, as defined in [RFC5155].  An authoritative server that   does not implement NSEC3 MAY still serve zones that use RSA/SHA-2   with NSEC denial of existence.Jansen                      Standards Track                     [Page 5]

RFC 5702                    DNSSEC RSA/SHA-2                October 20096.  Examples6.1.  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  192.0.2.91   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. kRCOH6u7l0QGy9qpC9                     l1sLncJcOKFLJ7GhiUOibu4teYp5VE9RncriShZNz85mwlMgNEa                     cFYK/lPtPiVYP4bwg==);{id = 9033}Jansen                      Standards Track                     [Page 6]

RFC 5702                    DNSSEC RSA/SHA-2                October 20096.2.  RSA/SHA-512 Key and Signature   Given a private key with the following values (in Base64):   Private-key-format: v1.2   Algorithm:       10 (RSASHA512)   Modulus:         0eg1M5b563zoq4k5ZEOnWmd2/BvpjzedJVdfIsDcMuuhE5SQ3pf                    Q7qmdaeMlC6Nf8DKGoUPGPXe06cP27/WRODtxXquSUytkO0kJDk                    8KX8PtA0+yBWwy7UnZDyCkynO00Uuk8HPVtZeMO1pHtlAGVnc8V                    jXZlNKdyit99waaE4s=   PublicExponent:  AQAB   PrivateExponent: rFS1IPbJllFFgFc33B5DDlC1egO8e81P4fFadODbp56V7sphKa6                    AZQCx8NYAew6VXFFPAKTw41QdHnK5kIYOwxvfFDjDcUGza88qbj                    yrDPSJenkeZbISMUSSqy7AMFzEolkk6WSn6k3thUVRgSlqDoOV3                    SEIAsrB043XzGrKIVE=   Prime1:          8mbtsu9Tl9v7tKSHdCIeprLIQXQLzxlSZun5T1n/OjvXSUtvD7x                    nZJ+LHqaBj1dIgMbCq2U8O04QVcK3TS9GiQ==   Prime2:          3a6gkfs74d0Jb7yL4j4adAif4fcp7ZrGt7G5NRVDDY/Mv4TERAK                    Ma0TKN3okKE0A7X+Rv2K84mhT4QLDlllEcw==   Exponent1:       v3D5A9uuCn5rgVR7wgV8ba0/KSpsdSiLgsoA42GxiB1gvvs7gJM                    MmVTDu/ZG1p1ZnpLbhh/S/Qd/MSwyNlxC+Q==   Exponent2:       m+ezf9dsDvYQK+gzjOLWYeKq5xWYBEYFGa3BLocMiF4oxkzOZ3J                    PZSWU/h1Fjp5RV7aPP0Vmx+hNjYMPIQ8Y5w==   Coefficient:     Je5YhYpUron/WdOXjxNAxDubAp3i5X7UOUfhJcyIggqwY86IE0Q                    /Bk0Dw4SC9zxnsimmdBXW2Izd8Lwuk8FQcQ==   The DNSKEY record for this key would be:   example.net.    3600  IN  DNSKEY  (256 3 10 AwEAAdHoNTOW+et86KuJOWRD                   p1pndvwb6Y83nSVXXyLA3DLroROUkN6X0O6pnWnjJQujX/AyhqFD                   xj13tOnD9u/1kTg7cV6rklMrZDtJCQ5PCl/D7QNPsgVsMu1J2Q8g                   pMpztNFLpPBz1bWXjDtaR7ZQBlZ3PFY12ZTSncorffcGmhOL                   );{id = 3740 (zsk), size = 1024b}   With this key, sign the following RRSet, consisting of 1 A record:   www.example.net. 3600  IN  A  192.0.2.91   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 10 3 3600 20300101000000                    20000101000000 3740 example.net. tsb4wnjRUDnB1BUi+t                    6TMTXThjVnG+eCkWqjvvjhzQL1d0YRoOe0CbxrVDYd0xDtsuJRa                    eUw1ep94PzEWzr0iGYgZBWm/zpq+9fOuagYJRfDqfReKBzMweOL                    DiNa8iP5g9vMhpuv6OPlvpXwm9Sa9ZXIbNl1MBGk0fthPgxdDLw                    =);{id = 3740}Jansen                      Standards Track                     [Page 7]

RFC 5702                    DNSSEC RSA/SHA-2                October 20097.  IANA Considerations   This document updates the IANA registry "DNS SECURITY ALGORITHM   NUMBERS -- per [RFC4035]" (http://www.iana.org/protocols).  The   following entries are added to the registry:                                             Zone  Trans.   Value   Description       Mnemonic    Signing    Sec.   References     8     RSA/SHA-256      RSASHA256          Y      *RFC 5702    10     RSA/SHA-512      RSASHA512          Y      *RFC 5702   * There has been no determination of standardization of the use of     this algorithm with Transaction Security.8.  Security Considerations8.1.  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 (seeSection 2.2 of [RFC4035]), 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.Jansen                      Standards Track                     [Page 8]

RFC 5702                    DNSSEC RSA/SHA-2                October 20099.  Acknowledgments   This document is a minor extension to [RFC4034].  Also, we try to   follow the documents [RFC3110] and [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, Scott Rose,   Michael St. Johns, and Wouter Wijngaards.10.  References10.1.  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",BCP 14,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              Version 2.1",RFC 3447, February 2003.Jansen                      Standards Track                     [Page 9]

RFC 5702                    DNSSEC RSA/SHA-2                October 2009   [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   Science Park 140   1098 XG Amsterdam   NL   EMail: jelte@NLnetLabs.nl   URI:http://www.nlnetlabs.nl/Jansen                      Standards Track                    [Page 10]