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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2671 (Obsoleted by RFC 6891) Summary: 2 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: April 11, 2011 NIST 6 October 8, 2010 8 Signaling Cryptographic Algorithm Understanding in DNSSEC 9 draft-crocker-dnssec-algo-signal-07 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 18 cryptographic algorithms they support. 20 Requirements Language 22 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 23 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 24 document are to be interpreted as described in RFC 2119 [RFC2119]. 26 Status of This Memo 28 This Internet-Draft is submitted to IETF in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF), its areas, and its working groups. Note that 33 other groups may also distribute working documents as Internet- 34 Drafts. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 The list of current Internet-Drafts can be accessed at 42 http://www.ietf.org/ietf/1id-abstracts.txt. 44 The list of Internet-Draft Shadow Directories can be accessed at 45 http://www.ietf.org/shadow.html. 47 This Internet-Draft will expire on April 11, 2011. 49 Copyright Notice 51 Copyright (c) 2010 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Signaling Algorithm Understood (AU) Using EDNS . . . . . . . . 3 70 3. Client Considerations . . . . . . . . . . . . . . . . . . . . . 4 71 3.1. Recommendations for Stub Clients . . . . . . . . . . . . . 5 72 3.2. Recursive Cache Considerations . . . . . . . . . . . . . . 5 74 4. Intermediate Middlebox Considerations . . . . . . . . . . . . . 5 76 5. Server Considerations . . . . . . . . . . . . . . . . . . . . . 5 78 6. Traffic Analysis Considerations . . . . . . . . . . . . . . . . 6 80 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 82 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 84 9. Normative References . . . . . . . . . . . . . . . . . . . . . 6 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 tells validators which cryptographic algorithm 93 was used to generate the digital signature. Authentication across 94 delegation boundries is maintained by storing a hash of a subzone's 95 key in the parent zone stored in a Delegation Signer (DS) RR. These 96 DS RR's contain a second code number to identify the hash algorithm 97 used to contruct the DS RR. 99 This draft sets out to specify a way for validating end-system 100 resolvers to tell a server which cryptographic and/or hash algorithms 101 they support in a DNS query. This is done using the EDNS attribute 102 values in the OPT meta-RR [RFC2671]. 104 This proposed EDNS option serves to measure the acceptance and use of 105 new digital signing and hash algorithms. This algorithm signaling 106 option can be used by zone administrators as a gauge to measure the 107 successful deployment of code that implements a newly deployed 108 digital signature or hash algorithm used with DNSSEC. A zone 109 administrator may be able to determine when to stop serving the old 110 algorithm when the server sees that all or almost all of its clients 111 signal that they are able to accept the new algorithm. 113 This draft does not seek to include another process for including new 114 algorithms for use with DNSSEC (see . 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 a set of algorithms it implements. 120 2. Signaling Algorithm Understood (AU) Using EDNS 122 The ENDS0 specification outlined in [RFC2671] defines a way to 123 include new options using a standardized mechanism. These options 124 are contained in the RDATA of the OPT meta-RR. This document defines 125 a new EDNS0 option for a client to signal which algorithms the client 126 supports. 128 The figure below shows how the signally attribute is defined in the 129 RDATA of the OPT RR specified in [RFC2671]: 131 0 8 16 132 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 133 | OPTION-CODE (TBD) | 134 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 135 | DIGITAL-SIG-LIST-LENGTH | 136 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 137 | ALG-CODE | ... \ 138 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 139 | DS-HASH-LIST-LENGTH | 140 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 141 | HASH-CODE | ... \ 142 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 144 OPTION-CODE is the code for the Algorithm Understood (AU) option. 145 Its value is fixed at TBD. 147 DIGITAL-SIG-LIST-LENGTH is the length of the list of digital 148 signature algorithms in octets. DNSSEC algorithm codes are 1 octet 149 long so this value is the number of octets. 151 ALG-CODE is the list of assigned values of DNSSEC zone signing 152 algorithms that the client indicates as understood. The values 153 SHOULD be in descending order of preference, with the most preferred 154 algorithm first. For example, if a validating client implements RSA/ 155 SHA-1, RSA/SHA-256 and prefers the latter, the value of ALG-CODE 156 would be: 8 (RSA/SHA-256), 5 (RSA/SHA-1). 158 DS-HASH-LIST-LENGTH is the length of the list of hash algorithms in 159 octets. DNSSEC DS hash codes are 1 octet long so this value is the 160 number of octets. 162 HASH-CODE is the list of assigned values of DNSSEC DS hash algorithms 163 that the client indicates as understood. Like the ALG-CODE above, 164 the values SHOULD be in descending order of preference, with the most 165 preferred algorithm first. 167 3. Client Considerations 169 A validating end-system resolver sets the AU option in the OPT 170 meta-RR when sending a query. The validating end-system resolver 171 sets the value(s) in the order of preference, with the most preferred 172 algorithm(s) first as described in section 2. The end-system 173 resolver MUST also set the DNSSEC-OK bit [RFC4035] to indicate that 174 it wishes to receive DNSSEC RRs in the response. 176 Note that when including the PRIVATEDNS (253) and/or the PRIVATEOID 177 (254) codes, the client only indicates that it understands one or 178 more private algorithms but does not indicate which algorithms. 180 3.1. Recommendations for Stub Clients 182 Typically, stub resolvers rely on an upstream recursive server (or 183 cache) to provide a response; any algorithm support on the stub 184 resolver's side could be overruled by the upstream recursive server. 185 The AU EDNS option is NOT RECOMMENDED for non-validating stub 186 clients. 188 The exception to the above is that validating stub resolvers which 189 set the CD bit in queries MAY set the AU option. In the most common 190 scenario, the validating stub indicates that it wishes to perform its 191 own validation (via the CD bit) and may therefore wish to indicate 192 which cryptographic algorithm(s) it supports. 194 3.2. Recursive Cache Considerations 196 DNSSEC validating recursive caches MAY set the AU option on any 197 outgoing query from the cache when performing recursion on behalf of 198 a non-DNSSEC aware stub client. If the stub indicates it is DNSSEC- 199 aware, but does not set the AU option in the query, the DNSSEC 200 validating recursive cache SHOULD NOT set the AU option to avoid 201 conflicts. 203 Forwarders that do not do validation or caching SHOULD copy the AU 204 option seen in received queries as they represent the wishes of the 205 validating downstream resolver that issued the original query. 207 4. Intermediate Middlebox Considerations 209 Intermediate middleboxes SHOULD copy the AU option seen in queries 210 from end system resolvers. If the system is validating, it SHOULD 211 also check for the presence of the CD bit in the query. If present, 212 the intermediate middlebox SHOULD copy the AU option as seen in the 213 query. If not set or if the DNSSEC-OK bit is not set, then the 214 validating intermediate middlebox MAY chose to ignore the AU option 215 in the query and MAY include its own preference as the AU option. 217 5. Server Considerations 219 When an authoritative server sees the AU option in the OPT meta-RR in 220 a request the normal algorithm for servicing requests is followed. 222 If the AU option is present but the DNSSEC-OK bit is not set, then 223 the authoritative server ignores the ALG-CODE list and does not 224 include any additional DNSSEC RRs in the response. 226 6. Traffic Analysis Considerations 228 Zone administrators that are planning or are in the process of 229 completing a cryptographic algorithm rollover operation should 230 monitor DNS query traffic and record the values of the AU option in 231 queries. This monitoring can measure the deployment of client code 232 that implements (and signals) certain algorithms. Exactly how to 233 capture DNS traffic and measure new algorithm adoption is beyond the 234 scope of this document. 236 Zone administrators can use this data to set plans for starting an 237 algorithm rollover and when older algorithms can be phased out 238 without disrupting the majority of clients. In order to keep this 239 disruption to a minimum, zone administrators should wait to complete 240 an algorithm rollover until a large majority of clients signal that 241 they understand the new algorithm. Note that clients that do not 242 implement the AU option may be older implementations which would also 243 not implement any newly deployed algorithm. 245 7. IANA Considerations 247 The algorithm codes used to identify DNSSEC algorithms has already 248 been established by IANA. This document does not seek to alter that 249 registry in any way. 251 This draft seeks to update the "DNS EDNS0 Options" registry by adding 252 the AU option and referencing this document. The code for the option 253 should be TBD. 255 8. Security Considerations 257 This document specifies a way for a client to signal its digital 258 signature algorithm preference to a cache or server. It is not meant 259 to be a discussion on algorithm superiority. The signal is an 260 optional code contained in the OPT meta-RR used with EDNS0. The goal 261 of this option is to signal new algorithm uptake in client code to 262 allow zone administrators to know when it is possible to complete an 263 algorithm rollover in a DNSSEC signed zone. 265 9. Normative References 267 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 268 Requirement Levels", BCP 14, RFC 2119, March 1997. 270 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", 271 RFC 2671, August 1999. 273 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 274 Rose, "DNS Security Introduction and Requirements", 275 RFC 4033, March 2005. 277 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 278 Rose, "Resource Records for the DNS Security Extensions", 279 RFC 4034, March 2005. 281 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 282 Rose, "Protocol Modifications for the DNS Security 283 Extensions", RFC 4035, March 2005. 285 Authors' Addresses 287 Steve Crocker 288 Shinkuro Inc. 289 5110 Edgemoor Lane 290 Bethesda, MD 20814 291 USA 293 EMail: steve@shinkuro.com 295 Scott Rose 296 NIST 297 100 Bureau Dr. 298 Gaithersburg, MD 20899 299 USA 301 Phone: +1-301-975-8439 302 EMail: scottr.nist@gmail.com