idnits 2.17.1 draft-ietf-dnsext-dnssec-algo-signal-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (September 24, 2012) is 4233 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-10) exists of draft-ietf-dnsext-rfc2671bis-edns0-09 -- Possible downref: Normative reference to a draft: ref. 'I-D.ietf-dnsext-rfc2671bis-edns0' Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNS Extensions Working Group S. Crocker 3 Internet-Draft Shinkuro Inc. 4 Intended status: Standards Track S. Rose 5 Expires: March 28, 2013 NIST 6 September 24, 2012 8 Signaling Cryptographic Algorithm Understanding in DNSSEC 9 draft-ietf-dnsext-dnssec-algo-signal-09 11 Abstract 13 The DNS Security Extensions (DNSSEC) were developed to provide origin 14 authentication and integrity protection for DNS data by using digital 15 signatures. These digital signatures can be generated using 16 different algorithms. This draft sets out to specify a way for 17 validating end-system resolvers to signal to a server which digital 18 signature and hash algorithms they support. 20 Requirements Language 22 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 23 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 24 "OPTIONAL" in this document are to be interpreted as described in RFC 25 2119 [RFC2119]. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on March 28, 2013. 44 Copyright Notice 46 Copyright (c) 2012 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Signaling DNSSEC Algorithm Understood (DAU), DS Hash 64 Understood (DHU) and NSEC3 Hash Understood (N3U) Using EDNS . . 3 66 3. Client Considerations . . . . . . . . . . . . . . . . . . . . . 5 67 3.1. Stub Resolvers . . . . . . . . . . . . . . . . . . . . . . 5 68 3.1.1. Validating Stub Resolvers . . . . . . . . . . . . . . . 5 69 3.1.2. Non-Validating Stub Resolvers . . . . . . . . . . . . . 5 70 3.2. Recursive Resolvers . . . . . . . . . . . . . . . . . . . . 5 71 3.2.1. Validating Recursive Resolvers . . . . . . . . . . . . 5 72 3.2.2. Non-validating Recursive Resolvers . . . . . . . . . . 6 74 4. Intermediate System Considerations . . . . . . . . . . . . . . 6 76 5. Server Considerations . . . . . . . . . . . . . . . . . . . . . 6 78 6. Traffic Analysis Considerations . . . . . . . . . . . . . . . . 6 80 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 82 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 84 9. Normative References . . . . . . . . . . . . . . . . . . . . . 7 86 1. Introduction 88 The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and 89 [RFC4035] were developed to provide origin authentication and 90 integrity protection for DNS data by using digital signatures. Each 91 digital signature RR (RRSIG) contains an algorithm code number. 92 These algorithm codes tell validators which cryptographic algorithm 93 was used to generate the digital signature. 95 Likewise, Delegation Signer (DS) RRs and NSEC3 RRs use a hashed value 96 as part of their RDATA and, like digital signature algorithms, these 97 hash algorithms have code numbers. All three algorithm codes (RRSIG/ 98 DNSKEY, DS and NSEC3) are maintained in unique IANA registries. 100 This draft sets out to specify a way for validating end-system 101 resolvers to tell a server in a DNS query which digital signature 102 and/or hash algorithms they support. This is done using the new EDNS 103 options specified below in Section 2 for use in the OPT meta-RR 104 [I-D.ietf-dnsext-rfc2671bis-edns0]. These three new EDNS option 105 codes are all OPTIONAL to implement and use. 107 These proposed EDNS options serve to measure the acceptance and use 108 of new digital signing algorithms. These signaling options can be 109 used by zone administrators as a gauge to measure the successful 110 deployment of code that implements newly deployed digital signature 111 algorithm, DS hash and NSEC3 hash algorithm used with DNSSEC. A zone 112 administrator is able to determine when to stop signing with a 113 superseded algorithm when the server sees that a significant number 114 of its clients signal that they are able to accept the new algorithm. 115 Note that this survey may be conducted over the period of years 116 before a tipping point is seen. 118 This draft does not seek to introduce another process for including 119 new algorithms for use with DNSSEC. It also does not address the 120 question of which algorithms are to be included in any official list 121 of mandatory or recommended cryptographic algorithms for use with 122 DNSSEC. Rather, this document specifies a means by which a client 123 query can signal the set of algorithms and hashes which it 124 implements. 126 2. Signaling DNSSEC Algorithm Understood (DAU), DS Hash Understood 127 (DHU) and NSEC3 Hash Understood (N3U) Using EDNS 129 The EDNS0 specification outlined in 130 [I-D.ietf-dnsext-rfc2671bis-edns0] defines a way to include new 131 options using a standardized mechanism. These options are contained 132 in the RDATA of the OPT meta-RR. This document defines three new 133 EDNS options for a client to signal which digital signature and/or 134 hash algorithms the client supports. These options can be used 135 independently of each other and MAY appear in any order in the OPT 136 RR. Each option code can appear only once in an OPT RR. 138 The figure below shows how each option is defined in the RDATA of the 139 OPT RR specified in [I-D.ietf-dnsext-rfc2671bis-edns0]: 141 0 8 16 142 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 143 | OPTION-CODE (TBD) | 144 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 145 | LIST-LENGTH | 146 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 147 | ALG-CODE | ... \ 148 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 150 OPTION-CODE is the code for the given signaling option. They are: 152 o DNSSEC Algorithm Understood (DAU) option for DNSSEC digital 153 signing algorithms. Its value is fixed at TBD1. 155 o DS Hash Understood (DHU) option for DS RR hash algorithms. Its 156 value is fixed at TBD2. 158 o NSEC3 Hash Understood (N3U) option for NSEC3 hash algorithms. Its 159 value is fixed at TBD3. 161 LIST-LENGTH is the length of the list of digital signature or hash 162 algorithm codes in octets. Each algorithm code occupies a single 163 octet. 165 ALG-CODE is the list of assigned values of DNSSEC zone signing 166 algorithms, DS hash algorithms, or NSEC3 hash algorithms (depending 167 on the OPTION-CODE in use) that the client declares to be supported. 168 The order of the code values can be arbitrary and MUST NOT be used to 169 infer preference. 171 If all three options are included in the OPT RR, there is a potential 172 for the OPT RR to take up considerable size in the DNS message. 173 However, in practical terms, including all three options is likely to 174 take up 22-32 octets (average of 6-10 digital signature algorithms, 175 3-5 DS hash algorithms and 1-5 NSEC3 hash algorithms) including the 176 EDNS option codes and option lengths in a potential future example. 178 3. Client Considerations 180 A validating end-system resolver sets the DAU, DHU and/or N3U option, 181 or combination thereof in the OPT meta-RR when sending a query. The 182 validating end-system resolver MUST also set the DNSSEC-OK bit 183 [RFC4035] to indicate that it wishes to receive DNSSEC RRs in the 184 response. 186 Note that the PRIVATEDNS (253) and/or the PRIVATEOID (254) digital 187 signature codes both cover a potentially wide range of algorithms and 188 are likely not useful to a server. There is no compelling reason for 189 a client to include these codes in its list of the DAU. Likewise, 190 clients MUST NOT include RESERVED codes in any of the options. 192 3.1. Stub Resolvers 194 Typically, stub resolvers rely on an upstream recursive server (or 195 cache) to provide a response. So optimal setting of the DAU, DSU and 196 N3U options depends on whether the stub resolver elects to perform 197 its own validation. 199 3.1.1. Validating Stub Resolvers 201 A validating stub resolver already (usually) sets the DO bit 202 [RFC4035] to indicate that it wishes to receive additional DNSSEC RRs 203 (i.e. RRSIG RRs) in the response. Such validating resolvers SHOULD 204 include the DAU, DHU and/or the N3U option(s) in the OPT RR when 205 sending a query. 207 3.1.2. Non-Validating Stub Resolvers 209 The DAU, DHU and N3U EDNS options MUST NOT be included by non- 210 validating stub resolvers. 212 3.2. Recursive Resolvers 214 3.2.1. Validating Recursive Resolvers 216 A validating recursive resolver sets the DAU, DHU and/or N3U 217 option(s) when performing recursion based on its list of algorithms 218 and any DAU, DHU and/or N3U option lists in the stub client query. 219 When the recursive server receives a query with one or more of the 220 options set, the recursive server MUST set the algorithm list to a 221 union of the stub client's list and the validating recursive 222 resolver's list. For example, if the recursive resolver's algorithm 223 list for the DAU option is (3, 5, 7) and the stub's algorithm list is 224 (7, 8), the final DAU algorithm list would be (3, 5, 7, 8). 226 If the client did include the DO and CD bits, but did not include the 227 DAU, DHU and/or N3U option(s) in the query, the validating recursive 228 resolver MAY include the option(s) with its own list in full. If one 229 or more of the options are missing, the validating recursive resolver 230 MAY include the missing options with its own list in full. 232 3.2.2. Non-validating Recursive Resolvers 234 Recursive resolvers that do not do validation MUST copy the DAU, DHU 235 and/or N3U option(s) seen in received queries as they represent the 236 wishes of the validating downstream resolver that issued the original 237 query. 239 4. Intermediate System Considerations 241 Intermediate proxies [RFC5625] that understand DNS are RECOMMENDED to 242 behave like a comparable recursive resolver when dealing with the 243 DAU, DHU and N3U options. 245 5. Server Considerations 247 When an authoritative server sees the DAU, DHU and/or N3U option(s) 248 in the OPT meta-RR in a request the normal algorithm for servicing 249 requests is followed. The options MUST NOT trigger any special 250 processing (e.g. RRSIG filtering in responses) on the server side. 252 If the options are present but the DNSSEC-OK (OK) bit is not set, the 253 server does not do any DNSSEC processing, including any recording of 254 the option(s). 256 6. Traffic Analysis Considerations 258 Zone administrators that are planning or are in the process of a 259 cryptographic algorithm rollover operation should monitor DNS query 260 traffic and record the number of queries, the presence of the OPT RR 261 in queries and the values of the DAU/DHU/N3U option(s) (if present). 262 This monitoring can be used to measure the deployment of client code 263 that implements (and signals) specific algorithms. Description of 264 the techniques used to capture DNS traffic and measure new algorithm 265 adoption is beyond the scope of this document. 267 Zone administrators that need to comply with changes to their 268 organization's security policy (with regards to cryptographic 269 algorithm use) can use this data to set milestone dates for 270 performing an algorithm rollover. For example, zone administrators 271 can use the data to determine when older algorithms can be phased out 272 without disrupting a significant number of clients. In order to keep 273 this disruption to a minimum, zone administrators should wait to 274 complete an algorithm rollover until a large majority of clients 275 signal that they recognize the new algorithm. This may be in the 276 order of years rather than months. 278 Note that clients that do not implement these options are likely to 279 be older implementations which would also not implement any newly 280 deployed algorithm. 282 7. IANA Considerations 284 The algorithm codes used to identify DNSSEC algorithms, DS RR hash 285 algorithms and NSEC3 hash algorithms have already been established by 286 IANA. This document does not seek to alter that registry in any way. 288 This draft seeks to update the "DNS EDNS Options" registry by adding 289 the DAU, DHU and N3U options and referencing this document. The code 290 for these options are TBD1, TBD2 and TBD3 respectively. 292 8. Security Considerations 294 This document specifies a way for a client to signal its digital 295 signature and hash algorithm knowledge to a cache or server. It is 296 not meant to be a discussion on algorithm superiority. The signals 297 are optional codes contained in the OPT meta-RR used with EDNS. The 298 goal of these options are to signal new algorithm uptake in client 299 code to allow zone administrators to know when it is possible to 300 complete an algorithm rollover in a DNSSEC signed zone. 302 There is a possibility that an eavesdropper or server could infer the 303 validator in use by a client by the presence of the AU options and/or 304 algorithm code list. This information leakage in itself is not very 305 useful to a potential attacker but it could be used to identify the 306 validator or narrow down the possible validator implementations in 307 use by a client, which could have a known vulnerability that could be 308 exploited by the attacker. 310 9. Normative References 312 [I-D.ietf-dnsext-rfc2671bis-edns0] Damas, J., Graff, M., and P. 313 Vixie, "Extension Mechanisms for 314 DNS (EDNS0)", draft-ietf-dnsext- 315 rfc2671bis-edns0-09 (work in 316 progress), August 2012. 318 [RFC2119] Bradner, S., "Key words for use 319 in RFCs to Indicate Requirement 320 Levels", BCP 14, RFC 2119, 321 March 1997. 323 [RFC4033] Arends, R., Austein, R., Larson, 324 M., Massey, D., and S. Rose, "DNS 325 Security Introduction and 326 Requirements", RFC 4033, 327 March 2005. 329 [RFC4034] Arends, R., Austein, R., Larson, 330 M., Massey, D., and S. Rose, 331 "Resource Records for the DNS 332 Security Extensions", RFC 4034, 333 March 2005. 335 [RFC4035] Arends, R., Austein, R., Larson, 336 M., Massey, D., and S. Rose, 337 "Protocol Modifications for the 338 DNS Security Extensions", 339 RFC 4035, March 2005. 341 [RFC5625] Bellis, R., "DNS Proxy 342 Implementation Guidelines", 343 BCP 152, RFC 5625, August 2009. 345 Authors' Addresses 347 Steve Crocker 348 Shinkuro Inc. 349 5110 Edgemoor Lane 350 Bethesda, MD 20814 351 USA 353 EMail: steve@shinkuro.com 355 Scott Rose 356 NIST 357 100 Bureau Dr. 358 Gaithersburg, MD 20899 359 USA 361 Phone: +1-301-975-8439 362 EMail: scottr.nist@gmail.com