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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNS Extensions O. Kolkman 3 Internet-Draft RIPE NCC 4 Expires: March 23, 2004 J. Schlyter 6 E. Lewis 7 ARIN 8 September 23, 2003 10 KEY RR Secure Entry Point Flag 11 draft-ietf-dnsext-keyrr-key-signing-flag-09 13 Status of this Memo 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that other 20 groups may also distribute working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at http:// 28 www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on March 23, 2004. 35 Copyright Notice 37 Copyright (C) The Internet Society (2003). All Rights Reserved. 39 Abstract 41 With the Delegation Signer (DS) resource record the concept of a key 42 acting as a secure entry point has been introduced. During 43 key-exchanges with the parent there is a need to differentiate secure 44 entry point keys from other keys in the KEY resource record set. A 45 flag bit in the KEY RR is defined to indicate that KEY is to be used 46 as a secure entry point. The flag bit is intended to assist in 47 oprational procedures to correctly generate DS resource records, or 48 to indicate what keys are intended for static configuration. The flag 49 bit is not to be used in the DNS verification protocol. This document 50 updates RFC 2535 and RFC 3445. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. The Secure Entry Point (SEP) Flag . . . . . . . . . . . . . . . 4 56 3. DNSSEC Protocol Changes . . . . . . . . . . . . . . . . . . . . 4 57 4. Operational Guidelines . . . . . . . . . . . . . . . . . . . . . 4 58 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 59 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 60 7. Internationalization Considerations . . . . . . . . . . . . . . 6 61 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6 62 Normative References . . . . . . . . . . . . . . . . . . . . . . 6 63 Informative References . . . . . . . . . . . . . . . . . . . . . 6 64 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 65 Intellectual Property and Copyright Statements . . . . . . . . . 8 67 1. Introduction 69 "All keys are equal but some keys are more equal than others" [6] 71 With the definition of the Delegation Signer Resource Record (DS RR) 72 [5] it has become important to differentiate between the zone keys 73 that are (to be) pointed to by parental DS RRs and other keys in the 74 zone. We refer to these keys as Secure Entry Point (SEP) keys. A 75 SEP key is either used to generate a DS RR or is distributed to 76 resolvers that use the key as the root of a trusted subtree[3]. 78 In early deployment tests, the use of two (kinds of) keys in each 79 zone has been prevalent. One key is used to sign just the zone's KEY 80 RR set and is the key referenced by a DS RR at the parent or 81 configured statically in a resolver. Another key is used to sign the 82 rest of the zone's data sets. The former key is called a key-signing 83 key (KSK) and the latter is called a zone-signing key (ZSK). In 84 practice there have been usually one of each kind of key, but there 85 will be multiples of each at times. 87 It should be noted that division of zone keys into KSK's and ZSK's is 88 not mandatory in any definition of DNSSEC, not even with the 89 introduction of the DS RR. But, in testing, this distinction has 90 been helpful when designing key roll over (key super-cession) 91 schemes. Given that the distinction has proven helpful, the labels 92 KSK and ZSK have begun to stick. 94 There is a need to differentiate between a KSK and a ZSK by the zone 95 administrator. This need is driven by knowing which keys are to be 96 sent for DS RRs, which keys are to be distributed to resolvers, and 97 which keys are fed to the signer application at the appropriate time. 99 The reason for the term "SEP" is a result of the observation that the 100 distinction between KSK and ZSK is only significant to the signer 101 element of the DNS. Servers, resolvers and verifiers do not need to 102 make the distinction. Further, distinguishing between a KSK and ZSK 103 requires more than one bit, as a key could be fulfilling both roles. 104 Therefore, we provide no definition for a ZSK bit and another for a 105 KSK bit, just a single bit to assist operational procedures to 106 correctly generate DS RRs, or to indicate what keys are intended for 107 static configuration. 109 In the flow between signer and (parental) key-collector and in the 110 flow between the signer and the resolver configuration it is 111 important to be able to differentiate the SEP keys from the other 112 keys in a KEY RR set. The SEP flag is to be of no interest to the 113 flow between the verifier and the authoritative data store. 115 The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED", 116 "RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be 117 interpreted as described in RFC2119 [1]. 119 2. The Secure Entry Point (SEP) Flag 121 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 122 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 124 | flags |S| protocol | algorithm | 125 | |E| | | 126 | |P| | | 127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 128 | / 129 / public key / 130 / / 131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 133 KEY RR Format 135 The SEP bit (TBD) in the flags field is assigned to be the secure 136 entry point flag. If the the bit is set to 1 the key is intended to 137 be used as secure entry point key. One SHOULD NOT assign special 138 meaning to the key if the bit is set to 0. This document assigns the 139 15th bit [4] as the SEP bit. This way operators can recognize the 140 secure entry point key by the even or odd-ness of the decimal 141 representation of the flag field. 143 3. DNSSEC Protocol Changes 145 The bit MUST NOT be used during the resolving and verification 146 process. The SEP flag is only used to provide a hint about the 147 different administrative properties of the key and therefore the use 148 of the SEP flag does not change the DNS resolution and resolution 149 protocol. 151 4. Operational Guidelines 153 The SEP bit is set by the key-generator and MAY be used by the zone 154 signer to decide whether the key is to be prepared for input to a DS 155 RR generation function. As the SEP bit is within the data that is 156 used to compute a KEY RR's footprint, changing the SEP bit will 157 change the identity of the key within DNS. 159 When a key pair is created, the operator needs to indicate whether 160 the SEP bit is to be set in the KEY RR. The SEP bit is recommended 161 whenever the public key of the key pair will be distributed to the 162 parent zone to build the authentication chain or if the public key is 163 to be distributed for static configuration in verifiers. 165 When signing a zone, it is intended that the key(s) with the SEP bit 166 set (if such keys exist) are used to sign the KEY RR set of the zone. 167 The same key can be used to sign the rest of the zone data too. It 168 is conceivable that not all keys with a SEP bit set will sign the KEY 169 RR set, such keys might be pending retirement or not yet in use. 171 When verifying a RR set, the SEP bit is not intended to play a role. 172 How the key is used by the verifier is not intended to be a 173 consideration at key creation time. 175 Although the SEP flag provides a hint on which key to be used as 176 trusted root, administrators can choose to ignore the fact that a KEY 177 has its SEP bit set or not when configuring a trusted root for their 178 resolvers. 180 Using the flag a key roll over can be automated. The parent can use 181 an existing trust relation to verify key sets in which a new key with 182 the SEP flag appears. 184 5. Security Considerations 186 As stated in Section 3 the flag is not to be used in the resolution 187 protocol or to determine the security status of a key. The flag is to 188 be used for administrative purposes only. 190 No trust in a key should be inferred from this flag - trust MUST be 191 inferred from an existing chain of trust or an out-of-band exchange. 193 Since this flag might be used for automating key exchanges, we think 194 the following consideration is in place. 196 Automated mechanisms for roll over of the DS RR might be vulnerable 197 to a class of replay attacks. This might happen after a key exchange 198 where a key set, containing two keys with the SEP flag set, is sent 199 to the parent. The parent verifies the key set with the existing 200 trust relation and creates the new DS RR from the key that the 201 current DS is not pointing to. This key exchange might be replayed. 202 Parents are encouraged to implement a replay defense. A simple 203 defense can be based on a registry of keys that have been used to 204 generate DS RRs during the most recent roll over. These same 205 considerations apply to entities that configure keys in resolvers. 207 6. IANA Considerations 209 [4] eliminates all flags field except for the zone key flag in the 210 KEY RR. We assign the 15'th bit as the SEP bit; the decimal 211 representation of the flagfield will then be odd for key-signing 212 keys. 214 7. Internationalization Considerations 216 Although SEP is a popular acronym in many different languages, there 217 are no internationalization considerations. 219 8. Acknowledgments 221 The ideas documented in this document are inspired by communications 222 we had with numerous people and ideas published by other folk. Among 223 others Mark Andrews, Miek Gieben, Olafur Gudmundsson, Daniel 224 Karrenberg, Dan Massey, Marcos Sanz and Sam Weiler have contributed 225 ideas and provided feedback. 227 This document saw the light during a workshop on DNSSEC operations 228 hosted by USC/ISI in August 2002. 230 Normative References 232 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 233 Levels", BCP 14, RFC 2119, March 1997. 235 [2] Eastlake, D., "Domain Name System Security Extensions", RFC 236 2535, March 1999. 238 [3] Lewis, E., "DNS Security Extension Clarification on Zone 239 Status", RFC 3090, March 2001. 241 [4] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource 242 Record (RR)", RFC 3445, December 2002. 244 Informative References 246 [5] Gudmundsson, O., "Delegation Signer Resource Record", 247 draft-ietf-dnsext-delegation-signer-14 (work in progress), May 248 2003. 250 [6] Orwell, G. and R. Steadman (illustrator), "Animal Farm; a Fairy 251 Story"", ISBN 0151002177 (50th anniversery edition), April 1996. 253 Authors' Addresses 255 Olaf M. Kolkman 256 RIPE NCC 257 Singel 256 258 Amsterdam 1016 AB 259 NL 261 Phone: +31 20 535 4444 262 EMail: olaf@ripe.net 263 URI: http://www.ripe.net/ 265 Jakob Schlyter 266 Karl Gustavsgatan 15 267 Goteborg SE-411 25 268 Sweden 270 EMail: jakob@schlyter.se 272 Edward P. Lewis 273 ARIN 274 3635 Concorde Parkway Suite 200 275 Chantilly, VA 20151 276 US 278 Phone: +1 703 227 9854 279 EMail: edlewis@arin.net 280 URI: http://www.arin.net/ 282 Intellectual Property Statement 284 The IETF takes no position regarding the validity or scope of any 285 intellectual property or other rights that might be claimed to 286 pertain to the implementation or use of the technology described in 287 this document or the extent to which any license under such rights 288 might or might not be available; neither does it represent that it 289 has made any effort to identify any such rights. Information on the 290 IETF's procedures with respect to rights in standards-track and 291 standards-related documentation can be found in BCP-11. 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