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Jansen 3 Internet-Draft NLnet Labs 4 Intended status: Standards Track June 04, 2009 5 Expires: December 6, 2009 7 Use of SHA-2 algorithms with RSA in DNSKEY and RRSIG Resource Records 8 for DNSSEC 9 draft-ietf-dnsext-dnssec-rsasha256-14 11 Status of this Memo 13 This Internet-Draft is submitted to IETF in full conformance with the 14 provisions of BCP 78 and BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on December 6, 2009. 34 Copyright Notice 36 Copyright (c) 2009 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents in effect on the date of 41 publication of this document (http://trustee.ietf.org/license-info). 42 Please review these documents carefully, as they describe your rights 43 and restrictions with respect to this document. 45 Abstract 47 This document describes how to produce RSA/SHA-256 and RSA/SHA-512 48 DNSKEY and RRSIG resource records for use in the Domain Name System 49 Security Extensions (DNSSEC, RFC 4033, RFC 4034, and RFC 4035). 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. DNSKEY Resource Records . . . . . . . . . . . . . . . . . . . 3 55 2.1. RSA/SHA-256 DNSKEY Resource Records . . . . . . . . . . . 3 56 2.2. RSA/SHA-512 DNSKEY Resource Records . . . . . . . . . . . 4 57 3. RRSIG Resource Records . . . . . . . . . . . . . . . . . . . . 4 58 3.1. RSA/SHA-256 RRSIG Resource Records . . . . . . . . . . . . 4 59 3.2. RSA/SHA-512 RRSIG Resource Records . . . . . . . . . . . . 5 60 4. Deployment Considerations . . . . . . . . . . . . . . . . . . 5 61 4.1. Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . 5 62 4.2. Signature Sizes . . . . . . . . . . . . . . . . . . . . . 5 63 5. Implementation Considerations . . . . . . . . . . . . . . . . 5 64 5.1. Support for SHA-2 signatures . . . . . . . . . . . . . . . 5 65 5.2. Support for NSEC3 Denial of Existence . . . . . . . . . . 5 66 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 6.1. RSA/SHA-256 Key and Signature . . . . . . . . . . . . . . 6 68 6.2. RSA/SHA-512 Key and Signature . . . . . . . . . . . . . . 7 69 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 70 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 71 8.1. SHA-1 versus SHA-2 Considerations for RRSIG Resource 72 Records . . . . . . . . . . . . . . . . . . . . . . . . . 8 73 8.2. Signature Type Downgrade Attacks . . . . . . . . . . . . . 8 74 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 75 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 76 10.1. Normative References . . . . . . . . . . . . . . . . . . . 9 77 10.2. Informative References . . . . . . . . . . . . . . . . . . 9 78 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10 80 1. Introduction 82 The Domain Name System (DNS) is the global hierarchical distributed 83 database for Internet Naming. The DNS has been extended to use 84 cryptographic keys and digital signatures for the verification of the 85 authenticity and integrity of its data. RFC 4033 [RFC4033], RFC 4034 86 [RFC4034], and RFC 4035 [RFC4035] describe these DNS Security 87 Extensions, called DNSSEC. 89 RFC 4034 describes how to store DNSKEY and RRSIG resource records, 90 and specifies a list of cryptographic algorithms to use. This 91 document extends that list with the algorithms RSA/SHA-256 and RSA/ 92 SHA-512, and specifies how to store DNSKEY data and how to produce 93 RRSIG resource records with these hash algorithms. 95 Familiarity with DNSSEC, RSA and the SHA-2 [FIPS.180-3.2008] family 96 of algorithms is assumed in this document. 98 To refer to both SHA-256 and SHA-512, this document will use the name 99 SHA-2. This is done to improve readability. When a part of text is 100 specific for either SHA-256 or SHA-512, their specific names are 101 used. The same goes for RSA/SHA-256 and RSA/SHA-512, which will be 102 grouped using the name RSA/SHA-2. 104 The term "SHA-2" is not officially defined, but is usually used to 105 refer to the collection of the algorithms SHA-224, SHA-256, SHA-384 106 and SHA-512. Since SHA-224 and SHA-384 are not used in DNSSEC, SHA-2 107 will only refer to SHA-256 and SHA-512 in this document. 109 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 110 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 111 document are to be interpreted as described in [RFC2119]. 113 2. DNSKEY Resource Records 115 The format of the DNSKEY RR can be found in RFC 4034 [RFC4034]. RFC 116 3110 [RFC3110] describes the use of RSA/SHA-1 for DNSSEC signatures. 118 2.1. RSA/SHA-256 DNSKEY Resource Records 120 RSA public keys for use with RSA/SHA-256 are stored in DNSKEY 121 resource records (RRs) with the algorithm number {TBA1}. 123 For interoperability, as in RFC 3110 [RFC3110], the key size of RSA/ 124 SHA-256 keys MUST NOT be less than 512 bits, and MUST NOT be more 125 than 4096 bits. 127 2.2. RSA/SHA-512 DNSKEY Resource Records 129 RSA public keys for use with RSA/SHA-512 are stored in DNSKEY 130 resource records (RRs) with the algorithm number {TBA2}. 132 The key size of RSA/SHA-512 keys MUST NOT be less than 1024 bits, and 133 MUST NOT be more than 4096 bits. 135 3. RRSIG Resource Records 137 The value of the signature field in the RRSIG RR follows the RSASSA- 138 PKCS1-v1_5 signature scheme, and is calculated as follows. The 139 values for the RDATA fields that precede the signature data are 140 specified in RFC 4034 [RFC4034]. 142 hash = SHA-XXX(data) 144 Here XXX is either 256 or 512, depending on the algorithm used, as 145 specified in FIPS PUB 180-3 [FIPS.180-3.2008], and "data" is the wire 146 format data of the resource record set that is signed, as specified 147 in RFC 4034 [RFC4034]. 149 signature = ( 00 | 01 | FF* | 00 | prefix | hash ) ** e (mod n) 151 Here "|" is concatenation, "00", "01", "FF" and "00" are fixed octets 152 of corresponding hexadecimal value, "e" is the private exponent of 153 the signing RSA key, and "n" is the public modulus of the signing 154 key. The FF octet MUST be repeated the exact number of times so that 155 the total length of the concatenated term in parentheses equals the 156 length of the modulus of the signer's public key ("n"). 158 The "prefix" is intended to make the use of standard cryptographic 159 libraries easier. These specifications are taken directly from the 160 specifications of RSASSA-PKCS1-v1_5 in PKCS #1 v2.1 section 8.2 161 [RFC3447], and EMSA-PKCS1-v1_5 encoding in PKCS #1 v2.1 section 9.2 162 [RFC3447]. The prefixes for the different algorithms are specified 163 below. 165 3.1. RSA/SHA-256 RRSIG Resource Records 167 RSA/SHA-256 signatures are stored in the DNS using RRSIG resource 168 records (RRs) with algorithm number {TBA1}. 170 The prefix is the ASN.1 DER SHA-256 algorithm designator prefix as 171 specified in PKCS #1 v2.1 [RFC3447]: 173 hex 30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20 175 3.2. RSA/SHA-512 RRSIG Resource Records 177 RSA/SHA-512 signatures are stored in the DNS using RRSIG resource 178 records (RRs) with algorithm number {TBA2}. 180 The prefix is the ASN.1 DER SHA-512 algorithm designator prefix as 181 specified in PKCS #1 v2.1 [RFC3447]: 183 hex 30 51 30 0d 06 09 60 86 48 01 65 03 04 02 03 05 00 04 40 185 4. Deployment Considerations 187 4.1. Key Sizes 189 Apart from the restrictions in section 2, this document will not 190 specify what size of keys to use. That is an operational issue and 191 depends largely on the environment and intended use. A good starting 192 point for more information would be NIST SP 800-57 [NIST800-57]. 194 4.2. Signature Sizes 196 In this family of signing algorithms, the size of signatures is 197 related to the size of the key, and not the hashing algorithm used in 198 the signing process. Therefore, RRSIG resource records produced with 199 RSA/SHA-256 or RSA/SHA-512 will have the same size as those produced 200 with RSA/SHA-1, if the keys have the same length. 202 5. Implementation Considerations 204 5.1. Support for SHA-2 signatures 206 DNSSEC aware implementations SHOULD be able to support RRSIG and 207 DNSKEY resource records created with the RSA/SHA-2 algorithms as 208 defined in this document. 210 5.2. Support for NSEC3 Denial of Existence 212 RFC 5155 [RFC5155] defines new algorithm identifiers for existing 213 signing algorithms, to indicate that zones signed with these 214 algorithm identifiers can use NSEC3 as well as NSEC records to 215 provide denial of existence. That mechanism was chosen to protect 216 implementations predating RFC5155 from encountering resource records 217 they could not know about. This document does not define such 218 algorithm aliases. 220 A DNSSEC validator that implements RSA/SHA-2 MUST be able to validate 221 negative answers in the form of both NSEC and NSEC3 with hash 222 algorithm 1, as defined in [RFC5155]. An authoritative server that 223 does not implement NSEC3 MAY still serve zones that use RSA/SHA-2 224 with NSEC denial of existence. 226 6. Examples 228 6.1. RSA/SHA-256 Key and Signature 230 Given a private key with the following values (in Base64): 232 Private-key-format: v1.2 233 Algorithm: 8 (RSASHA256) 234 Modulus: wVwaxrHF2CK64aYKRUibLiH30KpPuPBjel7E8ZydQW1HYWHfoGm 235 idzC2RnhwCC293hCzw+TFR2nqn8OVSY5t2Q== 236 PublicExponent: AQAB 237 PrivateExponent: UR44xX6zB3eaeyvTRzmskHADrPCmPWnr8dxsNwiDGHzrMKLN+i/ 238 HAam+97HxIKVWNDH2ba9Mf1SA8xu9dcHZAQ== 239 Prime1: 4c8IvFu1AVXGWeFLLFh5vs7fbdzdC6U82fduE6KkSWk= 240 Prime2: 2zZpBE8ZXVnL74QjG4zINlDfH+EOEtjJJ3RtaYDugvE= 241 Exponent1: G2xAPFfK0KGxGANDVNxd1K1c9wOmmJ51mGbzKFFNMFk= 242 Exponent2: GYxP1Pa7CAwtHm8SAGX594qZVofOMhgd6YFCNyeVpKE= 243 Coefficient: icQdNRjlZGPmuJm2TIadubcO8X7V4y07aVhX464tx8Q= 245 The DNSKEY record for this key would be: 247 example.net. 3600 IN DNSKEY (256 3 8 AwEAAcFcGsaxxdgiuuGmCkVI 248 my4h99CqT7jwY3pexPGcnUFtR2Fh36BponcwtkZ4cAgtvd4Qs8P 249 kxUdp6p/DlUmObdk= );{id = 9033 (zsk), size = 512b} 251 With this key, sign the following RRSet, consisting of 1 A record: 253 www.example.net. 3600 IN A 192.0.2.91 255 If the inception date is set at 00:00 hours on January 1st, 2000, and 256 the expiration date at 00:00 hours on January 1st, 2030, the 257 following signature should be created: 259 www.example.net. 3600 IN RRSIG (A 8 3 3600 20300101000000 260 20000101000000 9033 example.net. kRCOH6u7l0QGy9qpC9 261 l1sLncJcOKFLJ7GhiUOibu4teYp5VE9RncriShZNz85mwlMgNEa 262 cFYK/lPtPiVYP4bwg== ;{id = 9033} 264 6.2. RSA/SHA-512 Key and Signature 266 Given a private key with the following values (in Base64): 268 Private-key-format: v1.2 269 Algorithm: 10 (RSASHA512) 270 Modulus: 0eg1M5b563zoq4k5ZEOnWmd2/BvpjzedJVdfIsDcMuuhE5SQ3pf 271 Q7qmdaeMlC6Nf8DKGoUPGPXe06cP27/WRODtxXquSUytkO0kJDk 272 8KX8PtA0+yBWwy7UnZDyCkynO00Uuk8HPVtZeMO1pHtlAGVnc8V 273 jXZlNKdyit99waaE4s= 274 PublicExponent: AQAB 275 PrivateExponent: rFS1IPbJllFFgFc33B5DDlC1egO8e81P4fFadODbp56V7sphKa6 276 AZQCx8NYAew6VXFFPAKTw41QdHnK5kIYOwxvfFDjDcUGza88qbj 277 yrDPSJenkeZbISMUSSqy7AMFzEolkk6WSn6k3thUVRgSlqDoOV3 278 SEIAsrB043XzGrKIVE= 279 Prime1: 8mbtsu9Tl9v7tKSHdCIeprLIQXQLzxlSZun5T1n/OjvXSUtvD7x 280 nZJ+LHqaBj1dIgMbCq2U8O04QVcK3TS9GiQ== 281 Prime2: 3a6gkfs74d0Jb7yL4j4adAif4fcp7ZrGt7G5NRVDDY/Mv4TERAK 282 Ma0TKN3okKE0A7X+Rv2K84mhT4QLDlllEcw== 283 Exponent1: v3D5A9uuCn5rgVR7wgV8ba0/KSpsdSiLgsoA42GxiB1gvvs7gJM 284 MmVTDu/ZG1p1ZnpLbhh/S/Qd/MSwyNlxC+Q== 285 Exponent2: m+ezf9dsDvYQK+gzjOLWYeKq5xWYBEYFGa3BLocMiF4oxkzOZ3J 286 PZSWU/h1Fjp5RV7aPP0Vmx+hNjYMPIQ8Y5w== 287 Coefficient: Je5YhYpUron/WdOXjxNAxDubAp3i5X7UOUfhJcyIggqwY86IE0Q 288 /Bk0Dw4SC9zxnsimmdBXW2Izd8Lwuk8FQcQ== 290 The DNSKEY record for this key would be: 292 example.net. 3600 IN DNSKEY (256 3 10 AwEAAdHoNTOW+et86KuJOWRD 293 p1pndvwb6Y83nSVXXyLA3DLroROUkN6X0O6pnWnjJQujX/AyhqFD 294 xj13tOnD9u/1kTg7cV6rklMrZDtJCQ5PCl/D7QNPsgVsMu1J2Q8g 295 pMpztNFLpPBz1bWXjDtaR7ZQBlZ3PFY12ZTSncorffcGmhOL 296 );{id = 3740 (zsk), size = 1024b} 298 With this key, sign the following RRSet, consisting of 1 A record: 300 www.example.net. 3600 IN A 192.0.2.91 302 If the inception date is set at 00:00 hours on January 1st, 2000, and 303 the expiration date at 00:00 hours on January 1st, 2030, the 304 following signature should be created: 306 www.example.net. 3600 IN RRSIG (A 10 3 3600 20300101000000 307 20000101000000 3740 example.net. tsb4wnjRUDnB1BUi+t 308 6TMTXThjVnG+eCkWqjvvjhzQL1d0YRoOe0CbxrVDYd0xDtsuJRa 309 eUw1ep94PzEWzr0iGYgZBWm/zpq+9fOuagYJRfDqfReKBzMweOL 310 DiNa8iP5g9vMhpuv6OPlvpXwm9Sa9ZXIbNl1MBGk0fthPgxdDLw 311 =);{id = 3740} 313 7. IANA Considerations 315 This document updates the IANA registry "DNS SECURITY ALGORITHM 316 NUMBERS -- per [RFC4035] " 317 (http://www.iana.org/assignments/dns-sec-alg-numbers). The following 318 entries are added to the registry: 320 Zone Trans. 321 Value Description Mnemonic Signing Sec. References 322 {TBA1} RSA/SHA-256 RSASHA256 y * {this memo} 323 {TBA2} RSA/SHA-512 RSASHA512 y * {this memo} 325 * There has been no determination of standardization of the use of this 326 algorithm with Transaction Security. 328 8. Security Considerations 330 8.1. SHA-1 versus SHA-2 Considerations for RRSIG Resource Records 332 Users of DNSSEC are encouraged to deploy SHA-2 as soon as software 333 implementations allow for it. SHA-2 is widely believed to be more 334 resilient to attack than SHA-1, and confidence in SHA-1's strength is 335 being eroded by recently-announced attacks. Regardless of whether or 336 not the attacks on SHA-1 will affect DNSSEC, it is believed (at the 337 time of this writing) that SHA-2 is the better choice for use in 338 DNSSEC records. 340 SHA-2 is considered sufficiently strong for the immediate future, but 341 predictions about future development in cryptography and 342 cryptanalysis are beyond the scope of this document. 344 The signature scheme RSASSA-PKCS1-v1_5 is chosen to match the one 345 used for RSA/SHA-1 signatures. This should ease implementation of 346 the new hashing algorithms in DNSSEC software. 348 8.2. Signature Type Downgrade Attacks 350 Since each RRSet MUST be signed with each algorithm present in the 351 DNSKEY RRSet at the zone apex (see [RFC4035] Section 2.2), a 352 malicious party cannot filter out the RSA/SHA-2 RRSIG, and force the 353 validator to use the RSA/SHA-1 signature if both are present in the 354 zone. This should provide resilience against algorithm downgrade 355 attacks, if the validator supports RSA/SHA-2. 357 9. Acknowledgments 359 This document is a minor extension to RFC 4034 [RFC4034]. Also, we 360 try to follow the documents RFC 3110 [RFC3110] and RFC 4509 [RFC4509] 361 for consistency. The authors of and contributors to these documents 362 are gratefully acknowledged for their hard work. 364 The following people provided additional feedback and text: Jaap 365 Akkerhuis, Mark Andrews, Roy Arends, Rob Austein, Francis Dupont, 366 Miek Gieben, Alfred Hoenes, Paul Hoffman, Peter Koch, Michael St. 367 Johns, Scott Rose and Wouter Wijngaards. 369 10. References 371 10.1. Normative References 373 [FIPS.180-3.2008] 374 National Institute of Standards and Technology, "Secure 375 Hash Standard", FIPS PUB 180-3, October 2008. 377 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 378 Requirement Levels", RFC 2119, March 1997. 380 [RFC3110] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain 381 Name System (DNS)", RFC 3110, May 2001. 383 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 384 Rose, "DNS Security Introduction and Requirements", 385 RFC 4033, March 2005. 387 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 388 Rose, "Resource Records for the DNS Security Extensions", 389 RFC 4034, March 2005. 391 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 392 Rose, "Protocol Modifications for the DNS Security 393 Extensions", RFC 4035, March 2005. 395 10.2. Informative References 397 [NIST800-57] 398 Barker, E., Barker, W., Burr, W., Polk, W., and M. Smid, 399 "Recommendations for Key Management", NIST SP 800-57, 400 March 2007. 402 [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography 403 Standards (PKCS) #1: RSA Cryptography Specifications 404 Version 2.1", RFC 3447, February 2003. 406 [RFC4509] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer 407 (DS) Resource Records (RRs)", RFC 4509, May 2006. 409 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 410 Security (DNSSEC) Hashed Authenticated Denial of 411 Existence", RFC 5155, March 2008. 413 Author's Address 415 Jelte Jansen 416 NLnet Labs 417 Kruislaan 419 418 Amsterdam 1098VA 419 NL 421 Email: jelte@NLnetLabs.nl 422 URI: http://www.nlnetlabs.nl/