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'4') (Obsoleted by RFC 4033, RFC 4034, RFC 4035) Summary: 4 errors (**), 0 flaws (~~), 6 warnings (==), 4 comments (--). 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 28, 2004 J. Schlyter 6 E. Lewis 7 ARIN 8 September 28, 2003 10 KEY RR Secure Entry Point Flag 11 draft-ietf-dnsext-keyrr-key-signing-flag-10 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 28, 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 (RR) set. 45 A flag bit in the KEY RR is defined to indicate that KEY is to be 46 used as a secure entry point. The flag bit is intended to assist in 47 operational 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 . . . . . . . . . . . . . . . . . . . . . . 5 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 resource record (RR) set and is the key referenced by a DS RR at the 81 parent or configured statically in a resolver. Another key is used to 82 sign the rest of the zone's data sets. The former key is called a 83 key-signing key (KSK) and the latter is called a zone-signing key 84 (ZSK). In practice there have been usually one of each kind of key, 85 but there 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 In the flow between signer and (parental) key-collector and in the 100 flow between the signer and the resolver configuration it is 101 important to be able to differentiate the SEP keys from the other 102 keys in a KEY RR set. The SEP flag is to be of no interest to the 103 flow between the verifier and the authoritative data store. 105 The reason for the term "SEP" is a result of the observation that the 106 distinction between KSK and ZSK is made by the signer, a key could be 107 both a KSK and a ZSK. To be clear, the term SEP was coined to lessen 108 the confusion caused by the overlap. (Once this label was applied, it 109 had the side effect of removing the temptation to have a KSK flag bit 110 and a ZSK flag bit, setting on needing just one bit.) 112 The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED", 113 "RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be 114 interpreted as described in RFC2119 [1]. 116 2. The Secure Entry Point (SEP) Flag 118 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 119 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 1 120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 121 | flags |S| protocol | algorithm | 122 | |E| | | 123 | |P| | | 124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 125 | / 126 / public key / 127 / / 128 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 130 KEY RR Format 132 The SEP bit (TBD) in the flags field is assigned to be the secure 133 entry point flag. If the the bit is set to 1 the key is intended to 134 be used as secure entry point key. One SHOULD NOT assign special 135 meaning to the key if the bit is set to 0. This document assigns the 136 15'th bit [4] as the SEP bit. This way operators can recognize the 137 secure entry point key by the even or odd-ness of the decimal 138 representation of the flag field. 140 3. DNSSEC Protocol Changes 142 The bit MUST NOT be used during the resolving and verification 143 process. The SEP flag is only used to provide a hint about the 144 different administrative properties of the key and therefore the use 145 of the SEP flag does not change the DNS resolution protocol or the 146 resolution process. 148 4. Operational Guidelines 150 The SEP bit is set by the key-generator and MAY be used by the zone 151 signer to decide whether the key is to be prepared for input to a DS 152 RR generation function. The SEP bit is recommended to be set (to 1) 153 whenever the public key of the key pair will be distributed to the 154 parent zone to build the authentication chain or if the public key is 155 to be distributed for static configuration in verifiers. 157 When a key pair is created, the operator needs to indicate whether 158 the SEP bit is to be set in the KEY RR. As the SEP bit is within the 159 data that is used to compute the 'key tag field' in the SIG RR, 160 changing the SEP bit will change the identity of the key within DNS. 162 In other words, once a key is used to generate signatures, the 163 setting of the SEP bit is to remain constant. If not, a verifier will 164 not be able to find the relevant KEY RR. 166 When signing a zone, it is intended that the key(s) with the SEP bit 167 set (if such keys exist) are used to sign the KEY RR set of the zone. 168 The same key can be used to sign the rest of the zone data too. It 169 is conceivable that not all keys with a SEP bit set will sign the KEY 170 RR set, such keys might be pending retirement or not yet in use. 172 When verifying a RR set, the SEP bit is not intended to play a role. 173 How the key is used by the verifier is not intended to be a 174 consideration at key creation time. 176 Although the SEP flag provides a hint on which key to be used as 177 trusted root, administrators can choose to ignore the fact that a KEY 178 has its SEP bit set or not when configuring a trusted root for their 179 resolvers. 181 Using the flag a key roll over can be automated. The parent can use 182 an existing trust relation to verify key sets in which a new key with 183 the SEP flag appears. 185 5. Security Considerations 187 As stated in Section 3 the flag is not to be used in the resolution 188 protocol or to determine the security status of a key. The flag is to 189 be used for administrative purposes only. 191 No trust in a key should be inferred from this flag - trust MUST be 192 inferred from an existing chain of trust or an out-of-band exchange. 194 Since this flag might be used for automating key exchanges, we think 195 the following consideration is in place. 197 Automated mechanisms for roll over of the DS RR might be vulnerable 198 to a class of replay attacks. This might happen after a key exchange 199 where a key set, containing two keys with the SEP flag set, is sent 200 to the parent. The parent verifies the key set with the existing 201 trust relation and creates the new DS RR from the key that the 202 current DS is not pointing to. This key exchange might be replayed. 203 Parents are encouraged to implement a replay defense. A simple 204 defense can be based on a registry of keys that have been used to 205 generate DS RRs during the most recent roll over. These same 206 considerations apply to entities that configure keys in resolvers. 208 6. IANA Considerations 209 IANA considerations: The flag bits in the KEY RR are assigned by 210 IETF consensus. There is no action on IANA. 212 7. Internationalization Considerations 214 Although SEP is a popular acronym in many different languages, there 215 are no internationalization considerations. 217 8. Acknowledgments 219 The ideas documented in this document are inspired by communications 220 we had with numerous people and ideas published by other folk. Among 221 others Mark Andrews, Miek Gieben, Olafur Gudmundsson, Daniel 222 Karrenberg, Dan Massey, Scott Rose, Marcos Sanz and Sam Weiler have 223 contributed ideas and provided feedback. 225 This document saw the light during a workshop on DNSSEC operations 226 hosted by USC/ISI in August 2002. 228 Normative References 230 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 231 Levels", BCP 14, RFC 2119, March 1997. 233 [2] Eastlake, D., "Domain Name System Security Extensions", RFC 234 2535, March 1999. 236 [3] Lewis, E., "DNS Security Extension Clarification on Zone 237 Status", RFC 3090, March 2001. 239 [4] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource 240 Record (RR)", RFC 3445, December 2002. 242 Informative References 244 [5] Gudmundsson, O., "Delegation Signer Resource Record", 245 draft-ietf-dnsext-delegation-signer-15 (work in progress), June 246 2003. 248 [6] Orwell, G. and R. Steadman (illustrator), "Animal Farm; a Fairy 249 Story", ISBN 0151002177 (50th anniversary edition), April 1996. 251 Authors' Addresses 253 Olaf M. Kolkman 254 RIPE NCC 255 Singel 256 256 Amsterdam 1016 AB 257 NL 259 Phone: +31 20 535 4444 260 EMail: olaf@ripe.net 261 URI: http://www.ripe.net/ 263 Jakob Schlyter 264 Karl Gustavsgatan 15 265 Goteborg SE-411 25 266 Sweden 268 EMail: jakob@schlyter.se 270 Edward P. Lewis 271 ARIN 272 3635 Concorde Parkway Suite 200 273 Chantilly, VA 20151 274 US 276 Phone: +1 703 227 9854 277 EMail: edlewis@arin.net 278 URI: http://www.arin.net/ 280 Intellectual Property Statement 282 The IETF takes no position regarding the validity or scope of any 283 intellectual property or other rights that might be claimed to 284 pertain to the implementation or use of the technology described in 285 this document or the extent to which any license under such rights 286 might or might not be available; neither does it represent that it 287 has made any effort to identify any such rights. Information on the 288 IETF's procedures with respect to rights in standards-track and 289 standards-related documentation can be found in BCP-11. 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