idnits 2.17.1 draft-ietf-dnsext-dnssec-algo-signal-10.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 (April 08, 2013) is 4029 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) -- Possible downref: Normative reference to a draft: ref. 'I-D.ietf-dnsext-rfc2671bis-edns0' Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 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: October 10, 2013 NIST 6 April 08, 2013 8 Signaling Cryptographic Algorithm Understanding in DNSSEC 9 draft-ietf-dnsext-dnssec-algo-signal-10 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. The proposed extensions 19 allow the signaling of new algorithm uptake in client code to allow 20 zone administrators to know when it is possible to complete an 21 algorithm rollover in a DNSSEC signed zone. 23 Requirements Language 25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 26 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 27 "OPTIONAL" in this document are to be interpreted as described in RFC 28 2119 [RFC2119]. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on October 10, 2013. 47 Copyright Notice 48 Copyright (c) 2013 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 64 2. Signaling DNSSEC Algorithm Understood (DAU), DS Hash 65 Understood (DHU) and NSEC3 Hash Understood (N3U) Using EDNS . 3 66 3. Client Considerations . . . . . . . . . . . . . . . . . . . . 4 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 73 4. Intermediate System Considerations . . . . . . . . . . . . . 6 74 5. Server Considerations . . . . . . . . . . . . . . . . . . . . 6 75 6. Traffic Analysis Considerations . . . . . . . . . . . . . . . 6 76 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 77 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 78 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 81 1. Introduction 83 The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and 84 [RFC4035] were developed to provide origin authentication and 85 integrity protection for DNS data by using digital signatures. Each 86 digital signature RR (RRSIG) contains an algorithm code number. 87 These algorithm codes tell validators which cryptographic algorithm 88 was used to generate the digital signature. 90 Likewise, Delegation Signer (DS) RRs and NSEC3 RRs use a hashed value 91 as part of their RDATA and, like digital signature algorithms, these 92 hash algorithms have code numbers. All three algorithm codes (RRSIG/ 93 DNSKEY, DS and NSEC3) are maintained in unique IANA registries. 95 This draft sets out to specify a way for validating end-system 96 resolvers to tell a server in a DNS query which digital signature and 97 /or hash algorithms they support. This is done using the new EDNS 98 options specified below in Section 2 for use in the OPT meta-RR 99 [I-D.ietf-dnsext-rfc2671bis-edns0]. These three new EDNS option 100 codes are all OPTIONAL to implement and use. 102 These proposed EDNS options serve to measure the acceptance and use 103 of new digital signing algorithms. These signaling options can be 104 used by zone administrators as a gauge to measure the successful 105 deployment of code that implements newly deployed digital signature 106 algorithm, DS hash and NSEC3 hash algorithm used with DNSSEC. A zone 107 administrator is able to determine when to stop signing with a 108 superseded algorithm when the server sees that a significant number 109 of its clients signal that they are able to accept the new algorithm. 110 Note that this survey may be conducted over the period of years 111 before a tipping point is seen. 113 This draft does not seek to introduce another process for including 114 new algorithms for use with DNSSEC. It also does not address the 115 question of which algorithms are to be included in any official list 116 of mandatory or recommended cryptographic algorithms for use with 117 DNSSEC. Rather, this document specifies a means by which a client 118 query can signal the set of algorithms and hashes which it 119 implements. 121 2. Signaling DNSSEC Algorithm Understood (DAU), DS Hash Understood 122 (DHU) and NSEC3 Hash Understood (N3U) Using EDNS 124 The EDNS0 specification outlined in 125 [I-D.ietf-dnsext-rfc2671bis-edns0] defines a way to include new 126 options using a standardized mechanism. These options are contained 127 in the RDATA of the OPT meta-RR. This document defines three new 128 EDNS options for a client to signal which digital signature and/or 129 hash algorithms the client supports. These options can be used 130 independently of each other and MAY appear in any order in the OPT 131 RR. Each option code can appear only once in an OPT RR. 133 The figure below shows how each option is defined in the RDATA of the 134 OPT RR specified in [I-D.ietf-dnsext-rfc2671bis-edns0]: 136 0 8 16 137 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 138 | OPTION-CODE (TBD) | 139 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 140 | LIST-LENGTH | 141 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 142 | ALG-CODE | ... \ 143 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 145 OPTION-CODE is the code for the given signaling option. They are: 147 o DNSSEC Algorithm Understood (DAU) option for DNSSEC digital 148 signing algorithms. Its value is fixed at TBD1. 150 o DS Hash Understood (DHU) option for DS RR hash algorithms. Its 151 value is fixed at TBD2. 153 o NSEC3 Hash Understood (N3U) option for NSEC3 hash algorithms. Its 154 value is fixed at TBD3. 156 LIST-LENGTH is the length of the list of digital signature or hash 157 algorithm codes in octets. Each algorithm code occupies a single 158 octet. 160 ALG-CODE is the list of assigned values of DNSSEC zone signing 161 algorithms, DS hash algorithms, or NSEC3 hash algorithms (depending 162 on the OPTION-CODE in use) that the client declares to be supported. 163 The order of the code values can be arbitrary and MUST NOT be used to 164 infer preference. 166 If all three options are included in the OPT RR, there is a potential 167 for the OPT RR to take up considerable size in the DNS message. 168 However, in practical terms, including all three options is likely to 169 take up 22-32 octets (average of 6-10 digital signature algorithms, 170 3-5 DS hash algorithms and 1-5 NSEC3 hash algorithms) including the 171 EDNS option codes and option lengths in potential future examples. 173 3. Client Considerations 175 A validating end-system resolver sets the DAU, DHU and/or N3U option, 176 or combination thereof in the OPT meta-RR when sending a query. The 177 validating end-system resolver MUST also set the DNSSEC-OK bit 178 [RFC4035] to indicate that it wishes to receive DNSSEC RRs in the 179 response. 181 Note that the PRIVATEDNS (253) and/or the PRIVATEOID (254) digital 182 signature codes both cover a potentially wide range of algorithms and 183 are likely not useful to a server. There is no compelling reason for 184 a client to include these codes in its list of the DAU. Likewise, 185 clients MUST NOT include RESERVED codes in any of the options. 186 Likewise, a client is under no obligation to list every algorithm it 187 implements and MAY choose to only list algorithms the client wishes 188 to signal as understood. 190 Since the DAU, DHU and/or N3U options are only set in the query, if a 191 client sees these options in the response, no action needs to be 192 taken and the client MUST ignore the option values. 194 3.1. Stub Resolvers 196 Typically, stub resolvers rely on an upstream recursive server (or 197 cache) to provide a response. So optimal setting of the DAU, DSU and 198 N3U options depends on whether the stub resolver elects to perform 199 its own validation. 201 3.1.1. Validating Stub Resolvers 203 A validating stub resolver already (usually) sets the DO bit 204 [RFC4035] to indicate that it wishes to receive additional DNSSEC RRs 205 (i.e. RRSIG RRs) in the response. Such validating resolvers SHOULD 206 include the DAU, DHU and/or the N3U option(s) in the OPT RR when 207 sending a query. 209 3.1.2. Non-Validating Stub Resolvers 211 The DAU, DHU and N3U EDNS options MUST NOT be included by non- 212 validating stub resolvers. 214 3.2. Recursive Resolvers 216 3.2.1. Validating Recursive Resolvers 218 A validating recursive resolver sets the DAU, DHU and/or N3U 219 option(s) when performing recursion based on its list of algorithms 220 and any DAU, DHU and/or N3U option lists in the stub client query. 221 When the recursive server receives a query with one or more of the 222 options set, the recursive server MUST set the algorithm list for any 223 outgoing iterative queries for that resolution chain to a union of 224 the stub client's list and the validating recursive resolver's list. 225 For example, if the recursive resolver's algorithm list for the DAU 226 option is (3, 5, 7) and the stub's algorithm list is (7, 8), the 227 final DAU algorithm list would be (3, 5, 7, 8). 229 If the client did include the DO and CD bits, but did not include the 230 DAU, DHU and/or N3U option(s) in the query, the validating recursive 231 resolver MAY include the option(s) with its own list in full. If one 232 or more of the options are missing, the validating recursive resolver 233 MAY include the missing options with its own list in full. 235 Validating recursive resolvers MUST NOT set the DAU, DHU and/or N3U 236 option(s) in the final response to the stub client. 238 3.2.2. Non-validating Recursive Resolvers 240 Recursive resolvers that do not do validation MUST copy the DAU, DHU 241 and/or N3U option(s) seen in received queries as they represent the 242 wishes of the validating downstream resolver that issued the original 243 query. 245 4. Intermediate System Considerations 247 Intermediate proxies [RFC5625] (Section 4.4.2) that understand DNS 248 are RECOMMENDED to behave like a comparable recursive resolver when 249 dealing with the DAU, DHU and N3U options. 251 5. Server Considerations 253 When an authoritative server sees the DAU, DHU and/or N3U option(s) 254 in the OPT meta-RR in a request the normal algorithm for servicing 255 requests is followed. The options MUST NOT trigger any special 256 processing (e.g. RRSIG filtering in responses) on the server side. 258 If the options are present but the DNSSEC-OK (OK) bit is not set, the 259 server does not do any DNSSEC processing, including any recording of 260 the option(s). 262 If the server sees one (or more) of the options set with RESERVED 263 values, the server MAY ignore recoding of those values. 265 Authoritative servers MUST NOT set the DAU, DHU and/or N3U option(s) 266 on any responses. These values are only set in queries. 268 6. Traffic Analysis Considerations 269 Zone administrators that are planning or are in the process of a 270 cryptographic algorithm rollover operation should monitor DNS query 271 traffic and record the number of queries, the presence of the OPT RR 272 in queries and the values of the DAU/DHU/N3U option(s) (if present). 273 This monitoring can be used to measure the deployment of client code 274 that implements (and signals) specific algorithms. Description of 275 the techniques used to capture DNS traffic and measure new algorithm 276 adoption is beyond the scope of this document. 278 Zone administrators that need to comply with changes to their 279 organization's security policy (with regards to cryptographic 280 algorithm use) can use this data to set milestone dates for 281 performing an algorithm rollover. For example, zone administrators 282 can use the data to determine when older algorithms can be phased out 283 without disrupting a significant number of clients. In order to keep 284 this disruption to a minimum, zone administrators should wait to 285 complete an algorithm rollover until a large majority of clients 286 signal that they recognize the new algorithm. This may be in the 287 order of years rather than months. 289 Note that clients that do not implement these options are likely to 290 be older implementations which would also not implement any newly 291 deployed algorithm. 293 7. IANA Considerations 295 The algorithm codes used to identify DNSSEC algorithms, DS RR hash 296 algorithms and NSEC3 hash algorithms have already been established by 297 IANA. This document does not seek to alter that registry in any way. 299 This draft seeks to update the "DNS EDNS Options" registry by adding 300 the DAU, DHU and N3U options and referencing this document. The code 301 for these options are TBD1, TBD2 and TBD3 respectively. 303 8. Security Considerations 305 This document specifies a way for a client to signal its digital 306 signature and hash algorithm knowledge to a cache or server. It is 307 not meant to be a discussion on algorithm superiority. The signals 308 are optional codes contained in the OPT meta-RR used with EDNS. The 309 goal of these options are to signal new algorithm uptake in client 310 code to allow zone administrators to know when it is possible to 311 complete an algorithm rollover in a DNSSEC signed zone. 313 There is a possibility that an eavesdropper or server could infer the 314 validator in use by a client by the presence of the AU options and/or 315 algorithm code list. This information leakage in itself is not very 316 useful to a potential attacker but it could be used to identify the 317 validator or narrow down the possible validator implementations in 318 use by a client, which could have a known vulnerability that could be 319 exploited by the attacker. 321 9. Normative References 323 [I-D.ietf-dnsext-rfc2671bis-edns0] 324 Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 325 for DNS (EDNS(0))", draft-ietf-dnsext-rfc2671bis-edns0-10 326 (work in progress), December 2012. 328 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 329 Requirement Levels", BCP 14, RFC 2119, March 1997. 331 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 332 Rose, "DNS Security Introduction and Requirements", RFC 333 4033, March 2005. 335 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 336 Rose, "Resource Records for the DNS Security Extensions", 337 RFC 4034, March 2005. 339 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 340 Rose, "Protocol Modifications for the DNS Security 341 Extensions", RFC 4035, March 2005. 343 [RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines", BCP 344 152, RFC 5625, August 2009. 346 Authors' Addresses 348 Steve Crocker 349 Shinkuro Inc. 350 5110 Edgemoor Lane 351 Bethesda, MD 20814 352 USA 354 EMail: steve@shinkuro.com 356 Scott Rose 357 NIST 358 100 Bureau Dr. 359 Gaithersburg, MD 20899 360 USA 362 Phone: +1-301-975-8439 363 EMail: scottr.nist@gmail.com