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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) == Missing Reference: 'Q' is mentioned on line 166, but not defined == Missing Reference: 'R' is mentioned on line 167, but not defined == Missing Reference: 'A' is mentioned on line 166, but not defined == Missing Reference: 'B' is mentioned on line 166, but not defined == Missing Reference: 'C' is mentioned on line 180, but not defined == Missing Reference: 'D' is mentioned on line 168, but not defined == Missing Reference: 'SG-A' is mentioned on line 178, but not defined == Outdated reference: A later version (-11) exists of draft-ietf-btns-connection-latching-00 == Outdated reference: A later version (-07) exists of draft-ietf-btns-prob-and-applic-05 ** Downref: Normative reference to an Informational draft: draft-ietf-btns-prob-and-applic (ref. 'I-D.ietf-btns-prob-and-applic') == Outdated reference: A later version (-07) exists of draft-ietf-kitten-gssapi-channel-bindings-02 -- Possible downref: Normative reference to a draft: ref. 'I-D.ietf-nfsv4-channel-bindings' ** Obsolete normative reference: RFC 2408 (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 2409 (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 4306 (Obsoleted by RFC 5996) Summary: 6 errors (**), 0 flaws (~~), 15 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NETWORK WORKING GROUP N. Williams 3 Internet-Draft Sun 4 Expires: September 1, 2007 M. Richardson 5 SSW 6 February 28, 2007 8 Better-Than-Nothing-Security: An Unauthenticated Mode of IPsec 9 draft-ietf-btns-core-02.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on September 1, 2007. 36 Copyright Notice 38 Copyright (C) The IETF Trust (2007). 40 Abstract 42 This document specifies how to use the Internet Key Exchange (IKE) 43 protocols, such as IKEv1 and IKEv2, to setup "unauthenticated" 44 security associations (SAs) for use with the IPsec Encapsulating 45 Security Payload (ESP) and the IPsec Authentication Header (AH). No 46 IKE extensions are needed, but Peer Authorization Database (PAD) and 47 Security Policy Database (SPD) extensions are specified. 48 Unauthenticated IPsec is herein referred to by its popular acronym, 49 "BTNS" (Better Than Nothing Security). 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 54 1.1. Conventions used in this document . . . . . . . . . . . . . 3 55 2. BTNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 3. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . 6 57 3.1. Example #1: sgA . . . . . . . . . . . . . . . . . . . . . . 6 58 3.2. Example #2: Q . . . . . . . . . . . . . . . . . . . . . . . 8 59 3.3. Example #3: C . . . . . . . . . . . . . . . . . . . . . . . 9 60 3.4. Miscaellaneous examples . . . . . . . . . . . . . . . . . . 9 61 4. Security Considerations . . . . . . . . . . . . . . . . . . 10 62 4.1. Connection-Latching and Channel Binding . . . . . . . . . . 10 63 4.2. Leap-of-Faith (LoF) for BTNS . . . . . . . . . . . . . . . . 10 64 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 65 5.1. Normative References . . . . . . . . . . . . . . . . . . . . 12 66 5.2. Informative References . . . . . . . . . . . . . . . . . . . 12 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 14 68 Intellectual Property and Copyright Statements . . . . . . . 15 70 1. Introduction 72 Here we describe how to establish unauthenticated IPsec SAs using 73 IKEv1 [RFC2408] [RFC2409] or IKEv2 [RFC4306] and unauthenticated 74 public keys. No new on-the-wire protocol elements are added to IKE 75 or IKEv2. 77 The [RFC4301] processing model is assumed. 79 This document does not define an opportunistic BTNS mode of IPsec 80 whereby nodes may fallback on unprotected IP when their peers do not 81 support IKE or IKEv2, nor does it describe "leap-of-faith" modes, or 82 "connection latching." 84 See [I-D.ietf-btns-prob-and-applic] for the applicability and uses of 85 BTNS. 87 1.1. Conventions used in this document 89 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 90 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 91 document are to be interpreted as described in [RFC2119]. 93 2. BTNS 95 The IPsec processing model, IKE and IKEv2 are hereby modified as 96 follows: 98 o A new ID type is added, 'PUBLICKEY'; IDs of this type have public 99 keys as values. This ID type is not used on the wire. 101 o A BTNS-specific PAD entry. This entry is intended to be the last 102 entry in the PAD when BTNS is enabled. A peer that matches no 103 other PAD entries is to be "authenticated" by verifying that the 104 signature in its AUTH (or SIG) payload in the IKEv2 (or v1) 105 exchange with the public key from the peer's CERT payload. The 106 peer's ID MUST then be coerced to be of 'PUBLICKEY' type with the 107 peer's public key as its value. 109 o A new flag for SPD entries: 'BTNS_OK'. Traffic to/from peers that 110 match the BTNS PAD entry will only match SPD entries that have the 111 BTNS_OK flag set. The SPD may be searched by address or by ID (of 112 type PUBLICKEY, of course, for BTNS peers), as per the IPsec 113 processing model [RFC4301]; searching by ID in this case requires 114 creation of SPD entries that are bound to public key values (this 115 could be used to build "leap-of-faith" behaviour, for example). 117 Nodes MUST reject IKE_SA proposals from peers that match non-BTNS PAD 118 entries but fail to authenticate properly. 120 Nodes wishing to be treated as BTNS nodes by their peers SHOULD use 121 bare RSA key CERT payloads and MAY use certificates known not to have 122 been pre-shared with their peers or outside their trust anchors 123 (e.g., self-signed certificates). RSA keys for use in BTNS may be 124 generated at any time, but "connection latching" 125 [I-D.ietf-btns-connection-latching] requires that they remain 126 constant between IKE exchanges setting up SAs for latched 127 connections. 129 To preserve standard IPsec access control semantics BTNS responders 130 MUST NOT allow BTNS peers to assert addresses which could be asserted 131 by non-BTNS peers. This can be achieved by processing the PAD in 132 order both, when peers authenticate and when BTNS peers negotiate 133 child SAs -- in the first case the PAD is searched for a matching PAD 134 entry as usual, and in the second it is searched to make sure that 135 BTNS peers' asserted child SA traffic selectors do not conflict with 136 non-BTNS PAD entries. Note that in general, if there are multiple 137 PAD entries with wildcard matching on peer ID then all but the last 138 one should constrain the traffic selectors for matching peers. 140 Note that nodes may unwittingly match peers' BTNS PAD entries and be 141 authenticated as BTNS nodes. This may be used in specifying the 142 "latching" of traffic flows to peer IDs 143 [I-D.ietf-btns-connection-latching]. 145 3. Usage Scenarios 147 In order to explain the above rules a number of scenarios will be 148 postulated. The goal here is to demonstrate that the above rules are 149 both sufficient and required. 151 To explain the scenarios a reference diagram describing a canonical 152 network will be used. It is as follows: 154 [Q] [R] 155 AS1 . . AS2 156 [A]----+----[SG-A].......+....+.......[SG-B]-------[B] 157 ...... \ 158 ..PI.. ----[btns-B] 159 ...... 160 [btns-C].....+....+.......[btns-D] 162 Figure 1: Reference Network Diagram 164 In this diagram, there are six end-nodes: A, B, C and D. Two of the 165 systems are security gateways: SG-A, SG-B, protecting networks on 166 which [A] and [B] reside. There is a node [Q] which is IPsec and 167 BTNS capable, and node [R] is a simple node, with no IPsec or BTNS 168 capability. Nodes [C] and [D] are BTNS capable. We will examine 169 interactions between the BTNS enabled nodes, and the IPsec enabled 170 nodes. 172 Nodes C and Q have a fixed addresses. Node D non-fixed addresses. 174 PI is the Public Internet ("The Wild"). 176 3.1. Example #1: sgA 178 The machine that we will care about will be [SG-A], a firewall device 179 of some kind which we wish to configure to respond to BTNS 180 connections from [C] 182 SG-A has the following "VPN" PAD and SPD entries: 184 Child SA 185 Rule Remote ID IDs allowed SPD Search by 186 ---- --------- ----------- ------------- 187 1 by-IP 188 2 by-IP 189 3 PUBLICKEY:any ANY by-IP 191 The last entry is the BTNS entry. 193 Figure 2: SG-A PAD table 195 Here is any address that is not part of A's network, and is not 196 claimed by any other entry. Note that sgA's PAD entry has one and 197 only one wildcard PAD entry: the BTNS catch-all PAD entry, so, as 198 described in Section 2. 200 and are from [RFC4301] section 201 4.4.3 203 Rule Local Remote Next Layer BTNS Action 204 addr addr Protocol ok 205 ---- ----- ------ ---------- ---- ----------------------- 206 1 A R ANY N/A BYPASS 207 2 A Q ANY no PROTECT(ESP,tunnel,AES, 208 SHA256) 209 3 A B-net ANY no PROTECT(ESP,tunnel,AES, 210 SHA256) 211 4 A ANY ANY yes PROTECT(ESP,transport, 212 integr+conf) 214 Figure 3: SG-A SPD table 216 The processing by sgA of various peers then is as follows: 218 o Q does not match PAD entry #1, but does match PAD entry #2; PAD 219 processing stops, then the SPD is searched by Q's ID to find entry 220 #2; CHILD SAs are then allowed that have sgA's and Q's addresses 221 as the end-point addresses. 223 o sgB matches PAD entry #1; PAD processing stops, then the SPD is 224 searched by sgB's ID to find SPD entry #3; CHILD SAs are then 225 allowed that have sgA's address and any addresses from B's network 226 as the end-point addresses. 228 o R does not initiate any IKE_SAs; its traffic to A is bypassed by 229 SPD entry #1. 231 o C does not match PAD entries #1 or #2, but does match entry #3, 232 the BTNS wildcard PAD entry; the SPD is searched by C's address 233 and SPD entry #4 is matched. CHILD SAs are then allowed that have 234 sgA's address and C's address as the end-point addresses provided 235 that C's address is neither Q's nor any of B's (see Section 2). 237 o Rogue BTNS nodes attempting to assert Q's or B's addresses will 238 either match the PAD entries for Q or B and fail to authenticate 239 as Q or B, in which case they are rejected, or they will match PAD 240 entry #3 but will not be allowed to create CHILD SAs with Q's or 241 B's addresses as traffic selectors. 243 o Rogue BTNS nodes attempting to assert C's address are allowed. 244 Protection for C requires additional bindings of C's specific BTNS 245 ID (that is, its public key) to its traffic flows through 246 connection-latching and channel binding, or leap-of-faith, none of 247 which are described here. 249 3.2. Example #2: Q 251 Q is either a BITS or native IPsec implementation; if it is a native 252 implementation it may have IPsec-aware applications, specifically 253 NFSv4 (TCP port 2049). 255 In any case, Q wants to communicate with A generally, and with BTNS 256 peers for NFSv4 only. It's PAD and SPD are configured as follows: 258 Child SA 259 Rule Remote ID IDs allowed SPD Search by 260 ---- --------- ----------- ------------- 261 1 by-IP 262 2 PUBLICKEY:any ANY by-IP 264 The last entry is the BTNS entry. 266 Figure 4: Q PAD table 268 Rule Local Remote Next Layer BTNS Action 269 addr addr Protocol ok 270 ---- ----- ------ ---------- ---- ----------------------- 271 1 Q A ANY no PROTECT(ESP,tunnel,AES, 272 SHA256) 273 2 Q ANY ANY yes PROTECT(ESP,transport, 274 and integr+conf) 275 port 276 2049 278 Figure 5: SG-A SPD table 280 The same analysis shown above in Section 3.1 applies here with 281 respect to sgA, C and rogue peers, except that C is allowed only 282 access to the NFSv4 service on Q. Additionally sgB is treated as a 283 BTNS peer as it is not known to Q, and therefore any host behind sgB 284 can access the NFSv4 service on Q (and, because Q has no formal 285 relationship with sgB, rogues can impersonate B). 287 3.3. Example #3: C 289 C only supports BTNS and wants to use BTNS to protect NFSv4 traffic. 290 It's PAD and SPD are configured as follows: 292 Child SA 293 Rule Remote ID IDs allowed SPD Search by 294 ---- --------- ----------- ------------- 295 1 PUBLICKEY:any ANY by-IP 297 The last entry is the BTNS entry. 299 Figure 6: Q PAD table 301 Rule Local Remote Next Layer BTNS Action 302 addr addr Protocol ok 303 ---- ----- ------ ---------- ---- ----------------------- 304 1 C ANY ANY yes PROTECT(ESP,transport, 305 and integr+conf) 306 port 307 2049 309 2 C ANY ANY N/A BYPASS 311 Figure 7: SG-A SPD table 313 3.4. Miscaellaneous examples 315 If sgA were not BTNS-capable then it would not have PAD and SPD 316 entries #3 and #4, respectively. Then C would be rejected as usual 317 under the standard IPsec model [RFC4301]. 319 Similarly, if Q were not BTNS-capable then it would not have PAD and 320 SPD entries #2. Then C would be rejected as usual under the standard 321 IPsec model [RFC4301]. 323 4. Security Considerations 325 Unauthenticated security association negotiation is subject to MITM 326 attacks and should be used with care. Where security infrastructures 327 are lacking this may indeed be better than nothing. 329 Use with applications that bind authentication at higher network 330 layers to secure channels at lower layers may provide one secure way 331 to use unauthenticated IPsec, but this is not specified herein. 333 Use of multiple wildcard PAD entries can be problematic. Where it is 334 important that addresses and node identities be tightly bound it is 335 important that such PAD entries limit the addresses that matching 336 peers can assert for their CHILD SAs to non-overlapping address 337 spaces. In practice this may be difficult to configure; if it is not 338 feasible to configure systems in this way then either BTNS should not 339 be used or BTNS PAD entries should constrain matching peers only to 340 using services for which authentication is not normally necessary or 341 where IPsec-aware/connection-latching applications are used. 343 4.1. Connection-Latching and Channel Binding 345 BTNS is subject to MITM attacks. One way to protect against MITM 346 attacks subsequent to initial communications is to use "connection 347 latching" [I-D.ietf-btns-connection-latching], whereby ULPs cooperate 348 with IPsec in native IPsec implementations to bind individual packet 349 flows to sequences of SAs whose end-point IDs (public keys, in the 350 case of BTNS end-points) and other characteristics (e.g., quality of 351 protection) must all be the same. 353 MITMs can be detected by using application-layer authentication 354 frameworks and/or mechanisms, such as the GSS-API [RFC2743], with 355 channel binding [I-D.ietf-nfsv4-channel-bindings] 356 [I-D.ietf-kitten-gssapi-channel-bindings], where the channels to be 357 bound to application-layer authentication are latched connections and 358 where the channel bindings data strongly identify the end-points of 359 the latched connection (e.g., the public keys of the end-points). 361 4.2. Leap-of-Faith (LoF) for BTNS 363 "Leap of faith" is the term generally used for the habit of accepting 364 that a given key identifies a peer that one wanted to talk to without 365 strong evidence for that proposition. Specifically this is a common 366 mode of operation for Secure Shell [RFC4251] clients where, when a 367 server is encountered for the first time the client may ask the user 368 whether to accept the server's public key as its identity and, if so, 369 records the server's name (as given by the user) and public key in a 370 database. 372 Leap of Faith can work in a similar way for BTNS nodes, but it is 373 currently still being designed and specified by the IETF BTNS WG. 375 5. References 377 5.1. Normative References 379 [I-D.ietf-btns-connection-latching] 380 Williams, N., "IPsec Channels: Connection Latching", 381 draft-ietf-btns-connection-latching-00 (work in progress), 382 February 2006. 384 [I-D.ietf-btns-prob-and-applic] 385 Touch, J., "Problem and Applicability Statement for Better 386 Than Nothing Security (BTNS)", 387 draft-ietf-btns-prob-and-applic-05 (work in progress), 388 February 2007. 390 [I-D.ietf-kitten-gssapi-channel-bindings] 391 Williams, N., "Clarifications and Extensions to the GSS- 392 API for the Use of Channel Bindings", 393 draft-ietf-kitten-gssapi-channel-bindings-02 (work in 394 progress), June 2006. 396 [I-D.ietf-nfsv4-channel-bindings] 397 Williams, N., "On the Use of Channel Bindings to Secure 398 Channels", draft-ietf-nfsv4-channel-bindings-04 (work in 399 progress), June 2006. 401 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 402 Requirement Levels", BCP 14, RFC 2119, March 1997. 404 [RFC2408] Maughan, D., Schneider, M., and M. Schertler, "Internet 405 Security Association and Key Management Protocol 406 (ISAKMP)", RFC 2408, November 1998. 408 [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange 409 (IKE)", RFC 2409, November 1998. 411 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 412 Internet Protocol", RFC 4301, December 2005. 414 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 415 RFC 4306, December 2005. 417 5.2. Informative References 419 [RFC2743] Linn, J., "Generic Security Service Application Program 420 Interface Version 2, Update 1", RFC 2743, January 2000. 422 [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) 423 Protocol Architecture", RFC 4251, January 2006. 425 Authors' Addresses 427 Nicolas Williams 428 Sun Microsystems 429 5300 Riata Trace Ct 430 Austin, TX 78727 431 US 433 Email: Nicolas.Williams@sun.com 435 Michael C. Richardson 436 Sandelman Software Works 437 470 Dawson Avenue 438 Ottawa, ON K1Z 5V7 439 CA 441 Email: mcr@sandelman.ottawa.on.ca 442 URI: http://www.sandelman.ottawa.on.ca/ 444 Full Copyright Statement 446 Copyright (C) The IETF Trust (2007). 448 This document is subject to the rights, licenses and restrictions 449 contained in BCP 78, and except as set forth therein, the authors 450 retain all their rights. 452 This document and the information contained herein are provided on an 453 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 454 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 455 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 456 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 457 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 458 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 460 Intellectual Property 462 The IETF takes no position regarding the validity or scope of any 463 Intellectual Property Rights or other rights that might be claimed to 464 pertain to the implementation or use of the technology described in 465 this document or the extent to which any license under such rights 466 might or might not be available; nor does it represent that it has 467 made any independent effort to identify any such rights. 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