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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references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Experimental RFC: RFC 5739 == Outdated reference: A later version (-10) exists of draft-ietf-ipsecme-ddos-protection-00 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group V. Smyslov 3 Internet-Draft ELVIS-PLUS 4 Updates: 4301 (if approved) P. Wouters 5 Intended status: Standards Track Red Hat 6 Expires: October 22, 2015 April 20, 2015 8 The NULL Authentication Method in IKEv2 Protocol 9 draft-ietf-ipsecme-ikev2-null-auth-06 11 Abstract 13 This document specifies the NULL Authentication method and the 14 ID_NULL Identification Payload ID Type for the IKEv2 Protocol. This 15 allows two IKE peers to establish single-side authenticated or mutual 16 unauthenticated IKE sessions for those use cases where a peer is 17 unwilling or unable to authenticate or identify itself. This ensures 18 IKEv2 can be used for Opportunistic Security (also known as 19 Opportunistic Encryption) to defend against Pervasive Monitoring 20 attacks without the need to sacrifice anonymity. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on October 22, 2015. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 1.1. Conventions Used in This Document . . . . . . . . . . . . 3 58 2. Using the NULL Authentication Method . . . . . . . . . . . . . 5 59 2.1. Authentication Payload . . . . . . . . . . . . . . . . . . 5 60 2.2. Identification Payload . . . . . . . . . . . . . . . . . . 5 61 2.3. INITIAL_CONTACT Notification . . . . . . . . . . . . . . . 6 62 2.4. Interaction with Peer Authorization Database (PAD) . . . . 6 63 2.5. Traffic Selectors . . . . . . . . . . . . . . . . . . . . 7 64 3. Security Considerations . . . . . . . . . . . . . . . . . . . 8 65 3.1. Audit trail and peer identification . . . . . . . . . . . 8 66 3.2. Resource management and robustness . . . . . . . . . . . . 8 67 3.3. IKE configuration selection . . . . . . . . . . . . . . . 9 68 3.4. Networking topology changes . . . . . . . . . . . . . . . 9 69 4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 70 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 71 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 72 6.1. Normative References . . . . . . . . . . . . . . . . . . . 12 73 6.2. Informative References . . . . . . . . . . . . . . . . . . 12 74 Appendix A. Update of PAD processing in RFC4301 . . . . . . . . . 13 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 77 1. Introduction 79 The Internet Key Exchange Protocol version 2 (IKEv2), specified in 80 [RFC7296], provides a way for two parties to perform an authenticated 81 key exchange. While the authentication methods used by the peers can 82 be different, there is no method for one or both parties to remain 83 unauthenticated and anonymous. This document extends the 84 authentication methods to support unauthenticated and anonymous IKE 85 sessions. 87 In some situations mutual authentication is undesirable, superfluous 88 or impossible. The following three examples illustrate these 89 unauthenticated use cases: 91 o A user wants to establish an anonymous secure connection to a 92 server. In this situation the user should be able to authenticate 93 the server without presenting or authenticating to the server with 94 their own identity. This case uses a single-sided authentication 95 of the responder. 97 o A sensor that periodically wakes up from a suspended state wants 98 to send a measurement (e.g. temperature) to a collecting server. 99 The sensor must be authenticated by the server to ensure 100 authenticity of the measurement, but the sensor does not need to 101 authenticate the server. This case uses a single-sided 102 authentication of the initiator. 104 o Two peers without any trust relationship wish to defend against 105 widespread pervasive monitoring attacks as described in [RFC7258]. 106 Without a trust relationship, the peers cannot authenticate each 107 other. Opportunistic Security [RFC7435] states that 108 unauthenticated encrypted communication is preferred over 109 cleartext communication. The peers want to use IKE to setup an 110 unauthenticated encrypted connection, that gives them protection 111 against pervasive monitoring attacks. An attacker that is able 112 and willing to send packets can still launch a Man-in-the-Middle 113 attack to obtain a copy of the unencrypted communication. This 114 case uses a fully unauthenticated key exchange. 116 To meet these needs, this document introduces the NULL Authentication 117 method, and the ID_NULL ID type. This allows an IKE peer to 118 explicitly indicate that it is unwilling or unable to certify its 119 identity. 121 1.1. Conventions Used in This Document 123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 124 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 125 document are to be interpreted as described in [RFC2119]. 127 2. Using the NULL Authentication Method 129 In IKEv2, each peer independently selects the method to authenticate 130 itself to the other side. A peer may choose to refrain from 131 authentication by using the NULL Authentication method. If a peer 132 that requires authentication receives an AUTH payload containing the 133 NULL Authentication method type, it MUST return an 134 AUTHENTICATION_FAILED notification. If an initiator uses EAP, the 135 responder MUST NOT use the NULL Authentication Method (in conformance 136 with the section 2.16 of [RFC7296]). 138 NULL Authentication affects how the Authentication and the 139 Identification payloads are formed in the IKE_AUTH exchange. 141 2.1. Authentication Payload 143 NULL Authentication still requires a properly formed AUTH payload to 144 be present in the IKE_AUTH exchange messages, as the AUTH payload 145 cryptographically links the IKE_SA_INIT exchange messages with the 146 other messages sent over this IKE SA. 148 When using NULL Authentication, the content of the AUTH payload is 149 computed using the syntax of pre-shared secret authentication, 150 described in Section 2.15 of [RFC7296]. The value of SK_pi for the 151 initiator and SK_pr for the responder is used as the shared secret 152 for the content of the AUTH payload. Implementers should note this 153 means that authentication keys used by the two peers are different in 154 each direction. This is identical to how the content of the two last 155 AUTH payloads is generated for the non-key-generating EAP methods 156 (see Section 2.16 of [RFC7296] for details). 158 The IKEv2 Authentication Method value for NULL Authentication is 13. 160 2.2. Identification Payload 162 When a remote peer is not authenticated, any ID presented in the 163 Identification Data field of the ID payload cannot be validated. To 164 avoid the need of sending a bogus ID Type with placeholder data, this 165 specification defines a new ID Type, ID_NULL. The Identification 166 Data field of the ID payload for this ID Type MUST be empty. 168 If NULL Authentication is in use and anonymity is a concern then 169 ID_NULL SHOULD be used in the Identification payload. Some examples 170 of cases where a non-null identity type and value with NULL 171 Authentication can be used are logging, troubleshooting and in 172 scenarios where authentication takes place out of band after the IKE 173 SA is created (like in [AUTOVPN]). The content of the Identification 174 payload MUST NOT be used for any trust and policy checking in 175 IKE_AUTH exchange when NULL Authentication is employed (see Section 176 2.4 for details). 178 ID_NULL is primarily intended to be used with NULL Authentication but 179 could be used in other situations where the content of the 180 Identification Payload is not used. For example, ID_NULL could be 181 used when authentication is performed via raw public keys and the 182 identities are the keys themselves. These alternative uses of 183 ID_NULL should be described in their own respective documents. 185 The IKEv2 Identification Payload ID Type for ID_NULL is 13. 187 2.3. INITIAL_CONTACT Notification 189 The identity of a peer using NULL Authentication cannot be used to 190 find existing IKE SAs created by the same peer, as the peer identity 191 is not authenticated. For that reason the INITIAL_CONTACT 192 notifications MUST NOT be used to delete any other IKE SAs based on 193 the same peer identity without additional verification that the 194 existing IKE SAs with matching identity are actually stale. 196 The standard IKE Liveness Check procedure, described in Section 2.4 197 of [RFC7296], can be used to detect stale IKE SAs created by peers 198 using NULL Authentication. Inactive unauthenticated IKE SAs should 199 be checked periodically. Additionally, the event of creating a new 200 unauthenticated IKE SA can be used to trigger an out-of-order check 201 on existing unauthenticated IKE SAs, possibly limited to identical or 202 close-by IP addresses or to identical identities of the just created 203 IKE SA. 205 Implementations should weigh the resource consumption of sending 206 Liveness Checks against the memory usage of possible orphaned IKE 207 SAs. Implementations may choose to handle situations with thousands 208 of unauthenticated IKE SAs differently from situations with very few 209 such SAs. 211 2.4. Interaction with Peer Authorization Database (PAD) 213 Section 4.4.3 of [RFC4301] defines the Peer Authorization Database 214 (PAD), which provides the link between Security Policy Database (SPD) 215 and the IKEv2. The PAD contains an ordered list of records with 216 peers' identities along with corresponding authentication data and 217 Child SA authorization data. When the IKE SA is being established 218 the PAD is consulted to determine how the peer should be 219 authenticated and what Child SAs it is authorized to create. 221 When using NULL Authentication, the peer identity is not 222 authenticated and cannot be trusted. If ID_NULL is used with NULL 223 Authentication, there is no ID at all. The processing of PAD 224 described in Section 4.4.3 of [RFC4301] is updated for NULL 225 Authentication as follows. 227 NULL authentication is added as one of supported authentication 228 methods. This method does not have any authentication data. ID_NULL 229 is included into the list of allowed ID types. The matching rule for 230 ID_NULL consists only of whether this type is used, i.e. no actual ID 231 matching is done, as ID_NULL contains no identity data. 233 When using the NULL authentication method those matching rules MUST 234 include matching of a new flag in the SPD entry specifying whether 235 unauthenticated users are allowed to use that entry. I.e. each SPD 236 entry needs to be augmented to have a flag specifying whether it can 237 be used with NULL authentication or not, and only those rules that 238 explicitly have that flag turned on can be used with unauthenticated 239 connections. 241 The specific updates of text in Section 4.4.3 of [RFC4301] are listed 242 in Appendix A. 244 2.5. Traffic Selectors 246 Traffic Selectors and narrowing allow two IKE peers to mutually agree 247 on a traffic range for an IPsec SA. An unauthenticated peer must not 248 be allowed to use this mechanism to steal traffic that an IKE peer 249 intended to be for another host. This is especially problematic when 250 supporting anonymous IKE peers behind NAT, as such IKE peers build an 251 IPsec SA using their pre-NAT IP address that are different from the 252 source IP of their IKE packets. A rogue IKE peer could use malicious 253 Traffic Selectors to obtain access to traffic that the host never 254 intended to hand out. Implementations SHOULD restrict and isolate 255 all anonymous IKE peers from each other and itself and only allow it 256 access to itself and possibly its intended network ranges. 258 One method to achieve this is to always assign internal IP addresses 259 to unauthenticated IKE clients, as described in Section 2.19 of 260 [RFC7296]. Implementations may also use other techniques, such as 261 internal NAT and connection tracking. 263 Implementations MAY force unauthenticated IKE peers to single host- 264 to-host IPsec SAs. When using IPv6 this is not always possible, so 265 implementations MUST be able to assign full /64 address block to the 266 peer as described in [RFC5739], even if it is not authenticated. 268 3. Security Considerations 270 If authenticated IKE sessions are possible for a certain traffic 271 selector range between the peers, then unauthenticated IKE SHOULD NOT 272 be allowed for that traffic selector range. When mixing 273 authenticated and unauthenticated IKE with the same peer, policy 274 rules should ensure the highest level of security will be used to 275 protect the communication between the two peers. See [RFC7435] for 276 details. 278 If both peers use NULL Authentication, the entire key exchange 279 becomes unauthenticated. This makes the IKE session vulnerable to 280 active Man-in-the-Middle Attacks. 282 Using an ID Type other than ID_NULL with the NULL Authentication 283 Method may compromise the client's anonymity in case of an active 284 MITM attack. 286 IKE implementations without NULL Authentication have always performed 287 mutual authentication and were not designed for use with 288 unauthenticated IKE peers. Implementations might have made 289 assumptions that remote peers are identified. With NULL 290 Authentication these assumptions are no longer valid. Furthermore, 291 the host itself might have made trust assumptions or may not be aware 292 of the network topology changes that resulted from IPsec SAs from 293 unauthenticated IKE peers. 295 3.1. Audit trail and peer identification 297 With NULL Authentication an established IKE session is no longer 298 guaranteed to provide a verifiable (authenticated) entity known to 299 the system or network. Implementers that implement NULL 300 Authentication should ensure their implementation does not make any 301 assumptions that depend on IKE peers being "friendly", "trusted" or 302 "identifiable". 304 3.2. Resource management and robustness 306 Section 2.6 of [RFC7296] provides guidance for mitigation of "Denial 307 of Service" attacks by issuing COOKIES in response to resource 308 consumption of half-open IKE SAs. Furthermore, [DDOS-PROTECTION] 309 offers additional counter-measures in an attempt to distinguish 310 attacking IKE packets from legitimate IKE peers. 312 These defense mechanisms do not take into account IKE systems that 313 allow unauthenticated IKE peers. An attacker using NULL 314 Authentication is a fully legitimate IKE peer that is only 315 distinguished from authenticated IKE peers by having used NULL 316 Authentication. 318 While implementations should have been written to account for abusive 319 authenticated clients, any omission or error in handling abusive 320 clients may have gone unnoticed because abusive clients has been a 321 rare or non-existent problem. When adding support for 322 unauthenticated IKE peers, these implementation omissions and errors 323 will be found and abused by attackers. For example, an 324 unauthenticated IKE peer could send an abusive amount of Liveness 325 probes or Delete requests. 327 3.3. IKE configuration selection 329 Combining authenticated and unauthenticated IKE peers on a single 330 host can be dangerous, assuming the authenticated IKE peer gains more 331 or different access from non-authenticated peers (otherwise, why not 332 only allow unauthenticated peers). An unauthenticated IKE peer MUST 333 NOT be able to reach resources only meant for authenticated IKE peers 334 and MUST NOT be able to replace the Child SAs of an authenticated IKE 335 peer. 337 3.4. Networking topology changes 339 When a host relies on packet filters or firewall software to protect 340 itself, establishing an IKE SA and installing an IPsec SA might 341 accidentally circumvent these packet filters and firewall 342 restrictions, as the encrypted ESP (protocol 50) or ESPinUDP (UDP 343 port 4500) packets do not match the packet filters defined. IKE 344 peers supporting unauthenticated IKE MUST pass all decrypted traffic 345 through the same packet filters and security mechanisms as incoming 346 plaintext traffic. 348 4. Acknowledgments 350 The authors would like to thank Yaron Sheffer and Tero Kivinen for 351 their reviews, valuable comments and contributed text. 353 5. IANA Considerations 355 This document defines a new entry in the "IKEv2 Authentication 356 Method" registry: 358 13 NULL Authentication 360 This document also defines a new entry in the "IKEv2 Identification 361 Payload ID Types" registry: 363 13 ID_NULL 365 6. References 367 6.1. Normative References 369 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 370 Requirement Levels", BCP 14, RFC 2119, March 1997. 372 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 373 Internet Protocol", RFC 4301, December 2005. 375 [RFC5739] Eronen, P., Laganier, J., and C. Madson, "IPv6 376 Configuration in Internet Key Exchange Protocol Version 2 377 (IKEv2)", RFC 5739, February 2010. 379 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 380 Kivinen, "Internet Key Exchange Protocol Version 2 381 (IKEv2)", STD 79, RFC 7296, October 2014. 383 6.2. Informative References 385 [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an 386 Attack", BCP 188, RFC 7258, May 2014. 388 [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection 389 Most of the Time", RFC 7435, December 2014. 391 [AUTOVPN] Sheffer, Y. and Y. Nir, "The AutoVPN Architecture", Work 392 in Progress, draft-sheffer-autovpn-00, February 2014. 394 [DDOS-PROTECTION] 395 Nir, Y., "Protecting Internet Key Exchange (IKE) 396 Implementations from Distributed Denial of Service 397 Attacks", draft-ietf-ipsecme-ddos-protection-00 (work in 398 progress), October 2014. 400 Appendix A. Update of PAD processing in RFC4301 402 This appendix lists the specific updates of the text in Section 4.4.3 403 of [RFC4301] that should be followed when implementing NULL 404 Authentication. 406 A new item is added to the list of supported ID types in Section 407 4.4.3.1 409 o NULL ID (matches ID type only) 411 and the following text is added at the end of the section: 413 Added text: 414 The NULL ID type is defined as having no data. For this name type 415 the matching function is defined as comparing the ID type only. 417 A new item is added to the list of authentication data types in 418 Section 4.4.3.2 420 - NULL authentication 422 and the next paragraph is updated as follows: 424 Old: 425 For authentication based on an X.509 certificate [...] For 426 authentication based on a pre-shared secret, the PAD contains the 427 pre-shared secret to be used by IKE. 429 New: 430 For authentication based on an X.509 certificate [...] For 431 authentication based on a pre-shared secret, the PAD contains the 432 pre-shared secret to be used by IKE. For NULL authentication the 433 PAD contains no data. 435 In addition the following text is added at the end of Section 4.4.3.4 437 Added text: 438 When using the NULL authentication method implementations MUST 439 make sure that they do not mix authenticated and not-authenticated 440 SPD rules, i.e. implementations need to keep them separately, for 441 example by adding flag in SPD to tell whether NULL authentication 442 can be used or not for the entry. I.e. each SPD entry needs to be 443 augmented to have a flag specifying whether it can be used with 444 NULL authentication or not, and only those rules that explictly 445 have that flag set can be used with unauthenticated connections. 447 Authors' Addresses 449 Valery Smyslov 450 ELVIS-PLUS 451 PO Box 81 452 Moscow (Zelenograd) 124460 453 Russian Federation 455 Phone: +7 495 276 0211 456 Email: svan@elvis.ru 458 Paul Wouters 459 Red Hat 461 Email: pwouters@redhat.com