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Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 4282 (Obsoleted by RFC 7542) ** Obsolete normative reference: RFC 5996 (Obsoleted by RFC 7296) -- Obsolete informational reference (is this intentional?): RFC 3588 (Obsoleted by RFC 6733) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Y. Nir 3 Internet-Draft Check Point 4 Intended status: Experimental Q. Wu 5 Expires: June 23, 2013 Huawei 6 December 20, 2012 8 An IKEv2 Extension for Supporting ERP 9 draft-nir-ipsecme-erx-10 11 Abstract 13 This document updates the IKEv2 protocol, described in RFC 5996. 14 This extension allows an IKE Security Association (SA) to be created 15 and authenticated using the EAP Re-authentication Protocol extension 16 as described in RFC 6696. 18 Status of this Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on June 23, 2013. 35 Copyright Notice 37 Copyright (c) 2012 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 1. Introduction 52 IKEv2, as specified in section 2.16 of [RFC5996], allows 53 authentication of the initiator using an EAP method. Using EAP 54 significantly increases the count of round-trips required to 55 establish the IPsec SA, and also may require user interaction. This 56 makes it inconvenient to allow a single remote access client to 57 create multiple IPsec tunnels with multiple IPsec gateways that 58 belong to the same domain. 60 The EAP Re-authentication Protocol (ERP), as described in [RFC6696], 61 allows an EAP peer to authenticate to multiple authenticators, while 62 performing the full EAP method only once. Subsequent authentications 63 require fewer round-trips and no user interaction. 65 Bringing these two technologies together allows a remote access IPsec 66 client to create multiple tunnels with different gateways that belong 67 to a single domain, as well as using the keys from other contexts of 68 using EAP, such as network access within the same domain, to 69 transparently connect to VPN gateways within this domain. 71 Additionally, it allows for faster setting up of new tunnels when 72 previous tunnels have been torn down due to things like network 73 outage, device suspension, or temporarily moving out of range. This 74 is similar to the session resumption mechanism described in 75 [RFC5723], except that instead of a ticket stored by the client, the 76 re-authentication MSK (rMSK - see section 4.6 of RFC 6696) is used as 77 the session key stored on both the client and the AAA server. 79 1.1. Conventions Used in This Document 81 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 82 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 83 document are to be interpreted as described in [RFC2119]. 85 2. Usage Scenarios 87 This work is motivated by the following scenarios: 88 o Multiple tunnels for a single remote access VPN client. Suppose a 89 company has offices in New York City, Paris, and Shanghai. For 90 historical reasons, the email server is located in the Paris 91 office, while most of the servers hosting the company's intranet 92 are located in Shanghai, and the finance department servers are in 93 New York City. An employee using remote access VPN may need to 94 connect to servers from all three locations. While it is possible 95 to connect to a single gateway, and have that gateway route the 96 requests to the other gateways (perhaps through site to site VPN), 97 this is not efficient, and it is more desirable to have the client 98 initiate three different tunnels. It is, however, not desirable 99 to have the user type in a password three times. 100 o Roaming. In these days of mobile phones and tablets, users often 101 move from the wireless LAN in their office, where access may be 102 granted through 802.1x, to a cellular network where VPN is 103 necessary and back again. Both the VPN server and the 802.1x 104 access point are authenticators that connect to the same 105 Authentication, Authorization and Accounting (AAA) servers. So it 106 makes sense to make the transition smooth, without requiring user 107 interaction. The device still needs to detect whether it is 108 within the protected network, in which case it should not use VPN, 109 but this process is beyond the scope of this document. 110 [SecureBeacon] is a now-abandoned attempt at this. 111 o Resumption. If a device gets disconnected from an IKE peer, ERP 112 can be used to reconnect to the same gateway without user 113 intervention. 115 3. Protocol Outline 117 Supporting ERX requires an EAP payload in the first IKE_AUTH request. 118 This is a deviation from the rules in RFC 5996, so support needs to 119 be indicated through a Notify payload in the IKE_SA_INIT response. 120 This Notify serves the same purpose as the EAP-Initiate/Re-auth-Start 121 message of ERX, as specified in section 5.3.1 of RFC 6696. The 122 domain name included in the Domain-Name TLV as specified in section 123 5.3.1.1 of the same document. 125 A supporting initiator that has unexpired keys for this domain will 126 send the EAP_Initiate/Re-auth message in an EAP payload in the first 127 IKE_AUTH request. 129 The responder sends the EAP payload content to a backend AAA server. 130 If that server has a valid rMSK for that session, it sends those 131 along with an EAP-Finish/Re-auth message. The responder then 132 forwards the EAP-Finish/Re-auth message to the Initiator in an EAP 133 payload within the first IKE_AUTH response. 135 The initiator then sends an additional IKE_AUTH request, that 136 includes the AUTH payload which has been calculated using the rMSK in 137 the role of the MSK as described in sections 2.15 and 2.16 of RFC 138 5996. The responder replies similarly, and the IKE_AUTH exchange is 139 finished. 141 If the backend AAA server does not have valid keys for the Re-auth- 142 Start message, it sends back a normal EAP request, and no rMSK key. 143 EAP flow continues as in RFC 5996. 145 The following figure is adapted from appendixes C.1 and C.3 of RFC 146 5996, with most of the optional payloads removed. Note that the 147 EAP_Initiate/Re-auth message is added. 149 IKE_SA_INIT Exchange: 150 | init request --> SA, KE, Ni, 151 | 152 | init response <-- SA, KE, Nr, 153 | N[ERX_SUPPORTED] 155 IKE_AUTH Exchanges: 156 | first request --> EAP(EAP_Initiate/Re-auth), 157 | IDi, 158 | SA, TSi, TSr 159 | 160 | first response <-- IDr, [CERT+], AUTH, 161 | EAP(EAP-Finish/Re-auth) 162 | 163 | last request --> AUTH 164 | 165 | last response <-- AUTH, 166 | SA, TSi, TSr 168 The IDi payload MUST have ID Type ID_RFC822_ADDR and the data field 169 MUST contain the same value as the KeyName-NAI TLV in the 170 EAP_Initiate/Re-auth message. See Section 3.2 for details. 172 3.1. Clarification About EAP Codes 174 Section 3.16 of RFC 5996 enumerates the EAP codes in EAP messages 175 which are carried in EAP payloads. The enumeration goes only to 4. 176 It is not clear whether that list is supposed to be exhaustive or 177 not. 179 To clarify, an implementation conforming to this specification MUST 180 accept and transmit EAP messages with at least the codes for Initiate 181 and Finish (5 and 6) from RFC 6696, in addition to the four codes 182 enumerated in RFC 5996. This document is intentionally silent about 183 other EAP codes that are neither enumerated in RFC 5996 nor in that 184 document. 186 3.2. User Name in the Protocol 188 The authors, as well as participants of the HOKEY and IPsecME working 189 groups believe that all use cases for this extension to IKE have a 190 single backend AAA server doing both the authentication and the re- 191 authentication. The reasoning behind this is that IKE runs over the 192 Internet, and would naturally connect to the user's home network. 194 This section addresses instances where this is not the case. 196 Section 5.3.2 of RFC 6696 describes the EAP-Initiate/Re-auth packet, 197 which in the case of IKEv2 is carried in the first IKE_AUTH request. 198 This packet contains the KeyName-NAI TLV. This TLV contains the 199 username used in authentication. It is relayed to the AAA server in 200 the AccessRequest message, and is returned from the AAA server in the 201 AccessAccept message. 203 The username part of the NAI within the TLV is the EMSKName 204 ([RFC5295]) encoded in hexadecimal digits. The domain part is the 205 domain name of the home domain of the user. The username part is 206 ephemeral in the sense that a new one is generated for each full 207 authentication. This ephemeral value is not a good basis for making 208 policy decisions, and they are also a poor source of user 209 identification for the purposes of logging. 211 Instead, it is up to the implementation in the IPsec gateway to make 212 policy decisions based on other factors. The following list is by no 213 means exhaustive: 214 o In some cases the home domain name may be enough to make policy 215 decisions. If all users with a particular home domain get the 216 same authorization, then policy does not depend on the real user 217 name. Meaningful logs can still be issued by correlating VPN 218 gateway IKE events with AAA servers access records. 219 o Sometimes users receive different authorizations based on groups 220 they belong to. The AAA server can communicate such information 221 to the VPN gateway, for example using the CLASS attribute 222 ([RFC2865]) in RADIUS and Diameter ([RFC3588]). Logging again 223 depends on correlation with AAA servers. 224 o AAA servers may support extensions that allow them to communicate 225 with their clients (in our case - the VPN gateway) to push user 226 information. For example, a certain product integrates a RADIUS 227 server with the Lightweight Directory Access Protocol (LDAP - 228 [RFC4511]), so a client could query the server using LDAP and 229 receive the real record for this user. Others may provide this 230 data through vendor-specific extensions to RADIUS or DIAMETER. 232 In any case authorization is a major issue in deployments, if the 233 backend AAA server supporting the re-authentication is different from 234 the AAA server that had supported the original authentication. It is 235 up to the re-authenticating AAA server to provide the necessary 236 information for authorization. A conforming implementation of this 237 protocol MAY reject initiators for which it is unable to make policy 238 decisions because of these reasons. 240 4. ERX_SUPPORTED Notification 242 The Notify payload is as described in RFC 5996: 244 1 2 3 245 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 1 246 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 247 ! Next Payload !C! RESERVED ! Payload Length ! 248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 249 ! Protocol ID ! SPI Size ! ERX Notify Message Type ! 250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 251 ! Domain Name ! 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 o Protocol ID (1 octet) MUST be zero, as this message is related to 255 an IKE SA. 256 o SPI Size (1 octet) MUST be zero, in conformance with section 3.10 257 of RFC 5996. 258 o ERX Notify Message Type (2 octets) - MUST be xxxxx, the value 259 assigned for ERX. TBA by IANA. 260 o Domain Name (variable) - contains the domain name or realm, as 261 these terms are used in RFC 6696, and encoded as ASCII, as 262 specified in [RFC4282]. 264 5. Operational ConsiderationsS. 266 This specification changes the behavior of IKE peers, both initiators 267 and responders. The behavior of back-end AAA servers is not changed 268 by this specification, but they are required to support RFC 6696. 269 The same goes for the EAP client, if it's not integrated into the IKE 270 Initiator (for example, if it's an operating system component). 272 This specification is silent about key storage and key lifetimes on 273 either EAP client or EAP server. These issues are covered in 274 sections 3, 4, and 5 of RFC 6696. The key lifetime can be 275 communicated from the AAA server to the EAP client via the Lifetime 276 attribute in the EAP-Finish/Re-auth message. If the server does not 277 have a valid key, while the client does have one, regular EAP is used 278 (see Section 3). This should not happen if lifetimes are 279 communicated. In such a case, the IKEv2 initiator / EAP client MAY 280 alert the user and MAY log the event. Note that this does not 281 necessarily indicate an attack. It could simply be a loss of state 282 on the AAA server. 284 6. Security Considerations 286 The protocol extension described in this document extends the 287 authentication from one EAP context, which may or may not be part of 288 IKEv2, to an IKEv2 context. Successful completion of the protocol 289 proves to the authenticator, which in our case is a VPN gateway, that 290 the supplicant, or VPN client, has authenticated in some other EAP 291 context. 293 The protocol supplies the authenticator with the domain name with 294 which the supplicant has authenticated, but does not supply it with a 295 specific identity. Instead, the gateway receives an EMSKName, which 296 is an ephemeral ID. With this variant of the IKEv2 protocol, the 297 initiator never sends its real identity on the wire, while the server 298 does. This is different from the usual IKEv2 practice of the 299 initiator revealing its identity first. 301 If the domain name is sufficient to make access control decisions, 302 this is enough. If not, then the gateway needs to find out either 303 the real name or authorization information for that particular user. 304 This may be done using the AAA protocol or by some other federation 305 protocol, which is out of scope for this specification. 307 7. IANA Considerations 309 IANA is requested to assign a notify message type from the status 310 types range (16418-40959) of the "IKEv2 Notify Message Types" 311 registry with name "ERX_SUPPORTED". 313 8. Acknowledgements 315 The authors would like to thank Yaron Sheffer for comments and 316 suggested text that have contributed to this document. 318 9. References 320 9.1. Normative References 322 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 323 Requirement Levels", BCP 14, RFC 2119, March 1997. 325 [RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The 326 Network Access Identifier", RFC 4282, December 2005. 328 [RFC5295] Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri, 329 "Specification for the Derivation of Root Keys from an 330 Extended Master Session Key (EMSK)", RFC 5295, 331 August 2008. 333 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 334 "Internet Key Exchange Protocol: IKEv2", RFC 5996, 335 September 2010. 337 [RFC6696] Cao, Z., He, B., Shi, Y., Wu, Q., and G. Zorn, "EAP 338 Extensions for the EAP Re-authentication Protocol (ERP)", 339 RFC 6696, July 2012. 341 9.2. Informative References 343 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 344 "Remote Authentication Dial In User Service (RADIUS)", 345 RFC 2865, June 2000. 347 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 348 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 350 [RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol 351 (LDAP): The Protocol", RFC 4511, June 2006. 353 [RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange 354 Protocol Version 2 (IKEv2) Session Resumption", RFC 5273, 355 January 2010. 357 [SecureBeacon] 358 Sheffer, Y. and Y. Nir, "Secure Beacon: Securely Detecting 359 a Trusted Network", draft-sheffer-ipsecme-secure-beacon 360 (work in progress), June 2009. 362 Authors' Addresses 364 Yoav Nir 365 Check Point Software Technologies Ltd. 366 5 Hasolelim st. 367 Tel Aviv 67897 368 Israel 370 Email: ynir@checkpoint.com 371 Qin Wu 372 Huawei Technologies Co., Ltd. 373 101 Software Avenue, Yuhua District 374 Nanjing, JiangSu 210012 375 China 377 Email: sunseawq@huawei.com