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Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Sheng Jiang 2 Internet Draft Huawei Technologies Co., Ltd 3 Intended status: Informational Sean Shen 4 Expires: March 11, 2011 CNNIC 5 Tim Chown 6 University of Southampton 7 September 8, 2010 9 DHCPv6 and CGA Interaction: Problem Statement 11 draft-ietf-csi-dhcpv6-cga-ps-04.txt 13 Status of this Memo 15 This Internet-Draft is submitted in full conformance with the 16 provisions of BCP 78 and BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF). Note that other groups may also distribute working 20 documents as Internet-Drafts. The list of current Internet-Drafts is 21 at http://datatracker.ietf.org/drafts/current/. 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 This Internet-Draft will expire on March 11, 2011. 30 Copyright Notice 32 Copyright (c) 2010 IETF Trust and the persons identified as the 33 document authors. All rights reserved. 35 This document is subject to BCP 78 and the IETF Trust's Legal 36 Provisions Relating to IETF Documents 37 (http://trustee.ietf.org/license-info) in effect on the date of 38 publication of this document. Please review these documents 39 carefully, as they describe your rights and restrictions with respect 40 to this document. Code Components extracted from this document must 41 include Simplified BSD License text as described in Section 4.e of 42 the Trust Legal Provisions and are provided without warranty as 43 described in the Simplified BSD License. 45 Abstract 47 This document describes potential issues in the interaction between 48 DHCPv6 and Cryptographically Generated Addresses (CGAs). Firstly, the 49 scenario of using CGAs in DHCPv6 environments is discussed. Some 50 operations are clarified for the interaction of DHCPv6 servers and 51 CGA-associated hosts. We then also discuss how CGAs and DHCPv6 may 52 have mutual benefits for each other, including using CGAs in DHCPv6 53 operations to enhance its security features and using DHCPv6 to 54 provide the CGA generation function. 56 Table of Contents 58 1. Introduction.................................................3 59 2. Coexistence of DHCPv6 and CGA................................3 60 3. What DHCPv6 can do for CGA...................................4 61 4. What CGA can do for DHCPv6...................................5 62 5. Security Considerations......................................6 63 6. IANA Considerations..........................................7 64 7. Acknowledgements.............................................7 65 8. Change Log [RFC Editor please remove]........................7 66 9. References...................................................8 67 9.1. Normative References....................................8 68 Author's Addresses..............................................9 70 1. Introduction 72 The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315] 73 can assign addresses statefully. Although there are other ways to 74 assign IPv6 addresses [RFC4862, RFC5739], DHCPv6 is still useful when 75 an administrator requires more control over address assignments to 76 hosts. DHCPv6 can also be used to distribute other network 77 configuration information. 79 Cryptographically Generated Addresses (CGAs) [RFC3972] are IPv6 80 addresses for which the interface identifiers are generated by 81 computing a cryptographic one-way hash function from a public key and 82 auxiliary parameters. Associated with public & private key pairs, 83 CGAs are used in protocols, such as SEND [RFC3971] or SHIM6 84 [RFC5533], to provide address validation and integrity protection in 85 message exchanging. 87 This document describes potential issues in the interaction between 88 DHCPv6 and Cryptographically Generated Addresses (CGAs). Firstly, the 89 scenario of using CGAs in DHCPv6 environments is discussed. Some 90 operations are clarified for the interaction of DHCPv6 servers and 91 CGA-associated hosts. We then also discuss how CGAs and DHCPv6 may 92 have mutual benefits for each other, including using CGAs in DHCPv6 93 operations to enhance its security features and using DHCPv6 to 94 provide the CGA generation function. This document is designed to 95 generate further discussion on the specifics of if/how the ideas in 96 the document could be realized. 98 2. Coexistence of DHCPv6 and CGA 100 CGAs can be used with IPv6 Stateless Address Configuration [RFC4862]. 101 The public key system associated with the CGA address provides 102 message origin validation and integrity protection without the need 103 for negotiation and transportation of key materials. 105 The current CGA specifications do not mandate which device generates 106 a CGA address. In many cases, a CGA address is generated by the 107 associated key pair owner, which normally is also the host that will 108 use the CGA address. However, in a DHCPv6-managed network, hosts 109 should use IPv6 global addresses only from a DHCPv6 server. This 110 difference of roles needs to be carefully considered if there is a 111 requirement to use CGAs in DHCPv6-managed environments. 113 The current DHCPv6 specification [RFC3315] has a mechanism that could 114 be used to allow a host to self-generate a CGA for use in a DHCPv6- 115 managed environment, i.e. the DHCPv6 server can grant the use of 116 host-generated CGA addresses on request from the client. 118 Specifically, a node can request that a DHCPv6 server grants the use 119 of a self-generated CGA by sending a DHCPv6 Request message. This 120 DHCPv6 Request message contains an IA option including the CGA 121 address. Depending on whether the CGA satisfies the CGA-related 122 configuration parameters of the network, the DHCPv6 server can then 123 send an acknowledgement to the node to either grant the use of the 124 CGA or to indicate that the node must generate a new CGA with the 125 correct CGA-related configuration parameters of the network. In the 126 meantime the DHCPv6 server may log the requested address/host 127 combination. 129 3. What DHCPv6 can do for CGA 131 In the current CGA specifications there is a lack of procedures to 132 enable central management of CGA generation. Administrators should be 133 able to configure parameters used to generate CGAs. DHCPv6 could be 134 used to assign subnet prefixes or certificates to CGA address owners. 135 In some scenarios, the administrator may further want to enforce some 136 parameters, in particular the necessary security-related parameters 137 such as the SEC value. 139 In the CGA generation procedure, the generation of the Modifier field 140 of a CGA address is computationally intensive. This operation can 141 lead to apparent slow performance and/or battery consumption problems 142 for end hosts with limited computing ability and/or restricted 143 battery power (e.g. mobile devices). In such cases, a mechanism to 144 delegate the computation of the modifier would be desirable. It is 145 possible that the whole CGA generation procedure could be delegated 146 to the DHCPv6 server. This would be especially useful for large SEC 147 values. 149 Generating a key pair, which will be used to generate a CGA, also 150 requires a notable computation. Generation and distribution of a key 151 pair can also be done by a DHCPv6 server. Of course, when designing 152 these new functions, one should carefully consider the impact on 153 security. However, the security considerations of specific solutions 154 are out of scope of this document. 156 New DHCPv6 options could be defined to carry management parameters 157 from a DHCPv6 server to the client that wishes to use a CGA. A new 158 DHCPv6 prefix assignment option could be defined to propagate a 159 subnet prefix. More DHCPv6 options may be defined to propagate 160 additional CGA-relevant configuration information, such as the SEC 161 value, certificate information, SEND proxy information, etc. 163 It may be possible to define a delegation operation that allows a 164 client to pass computations to a DHCPv6 server, by introducing new 165 DHCPv6 option(s). A node could thus initiate a DHCPv6 request to the 166 DHCPv6 server requesting the computation of the Modifier or the CGA. 167 The DHCPv6 server could then either compute the Modifier by itself, 168 or redirect the computation requirement to another server. Once the 169 DHCPv6 server generates (or obtains from the redirected computational 170 server) the Modifier or the CGA address, it can respond to the node 171 with the Modifier or the resulting address and the corresponding CGA 172 Parameters data structure. 174 Depending on the scenario, the configuration information needed to 175 generate CGAs (including a SEC value, a subnet prefix, a modifier, a 176 public key, a Collision Count value and any Extension Fields) may be 177 provided by either hosts or DHCPv6 servers. A DHCPv6 server might 178 receive from hosts the configuration information customized by hosts, 179 generate CGAs by using configuration information provided by both 180 parties and deliver CGAs and their associated CGA Parameters data 181 structures to hosts. The details of such potential new methods need 182 to be defined clearly in the solution specifications. 184 New DHCPv6 options may be defined to support the interactions that 185 are required when a DHCPv6 server generates a key pair for hosts. 187 When designing such solutions, the designer should thoroughly 188 consider the impact on DHCPv6 model and the security of CGA usage. In 189 order to be compatible with DHCPv6, the configuring procedure of CGA 190 parameters should be compatible with the current DHCPv6 definition. 191 When a DHCP6 server configures CGA parameters, integrity protection 192 may be needed to avoid attacks, such as downgrade attack. 194 4. What CGA can do for DHCPv6 196 DHCPv6 is vulnerable to various attacks, e.g. fake address attacks 197 where a 'rogue' DHCPv6 server responds with incorrect address 198 information. A malicious rogue DHCPv6 server can also provide 199 incorrect configuration to the client in order to divert the client 200 to communicate with malicious services, like DNS or NTP. It may also 201 mount a Denial of Service attack through mis-configuration of the 202 client that causes all network communication from the client to fail. 203 A rogue DHCPv6 server may also collect some critical information from 204 the client. Attackers may be able to gain unauthorized access to some 205 resources, such as network access. See Section 23 [RFC3315]. 207 In the basic DHCPv6 specifications, regular IPv6 addresses are used. 208 However, DHCPv6 servers, relay agents and clients could use CGAs as 209 their own addresses. A DHCPv6 message (from either a server, relay 210 agent or client) with a CGA as source address can carry the CGA 211 Parameters data structure and a digital signature. The receiver can 212 verify both the CGA and signature, then process the payload of the 213 DHCPv6 message only if the validation is successful. A CGA option 214 with an address ownership proof mechanism and a signature option with 215 a corresponding verification mechanism may be introduced into DHCPv6 216 protocol. With these two new options, the receiver of a DHCPv6 217 message can verify the sender address of the DHCPv6 message, which 218 improves communication security of DHCPv6 messages. CGAs can be used 219 for all DHCPv6 messages/processes as long as CGAs are available on 220 the sender side. 222 Using CGAs in DHCPv6 protocol can efficiently improve the security of 223 DHCPv6. The address of a DHCPv6 message sender (which can be a DHCPv6 224 server, a reply agent or a client) can be verified by a receiver. 225 Also, the integrity of the sent data is provided if they are signed 226 with the private key associated to the public key used to generate 227 the CGA. The usage of CGA with pre-configured authorization, as 228 introduced in next paragraph, can efficiently avoid the 229 abovementioned attacks. It improves the communication security of 230 DHCPv6 interactions. The usage of CGAs can also avoid DHCPv6's 231 dependence on IPsec [RFC3315] in relay scenarios. This mechanism is 232 applicable in environments where physical security on the link is not 233 assured (such as over certain wireless infrastructures) or where 234 available security mechanisms are not sufficient, and attacks on 235 DHCPv6 are a concern. 237 A CGA generated from an unauthorized public & private key pair can 238 prove the source address ownership and provide data integrity 239 protection. Furthermore, a CGA generated from a certificated public & 240 private key pair can also achieve authorization for DHCPv6 servers or 241 relays, or on another direction, user authorization. The public keys 242 may be pre-configured on both parties of communication or have a 243 third party authority available for users to retrieve public keys. 244 The public keys will be used for users to generate CGAs and verify 245 CGAs and signatures. The pre-configuration can also include 246 configuring more CGA parameters such as SEC value or more depend on 247 policies. The pre-configuration can even be the whole CGA and related 248 parameters, but in this case the address will be fixed. It may 249 increase the vulnerability to, e.g., brute force attacks. 251 5. Security Considerations 253 As Section 4 of this document has discussed, CGAs can provide 254 additional security features for DHCPv6. However, in defining 255 solutions using DHCPv6 to configure CGAs, as suggested in Section 3 256 of this document, careful consideration is required to evaluate 257 whether the new mechanism introduces new security vulnerabilities. 259 When DHCPv6 is used to manage CGAs, CGA relevant information is 260 stored in a central repository, DHCPv6 server. It does not increase 261 privacy risks. The CGA relevant information is only exposed to the 262 network management plane. The privacy risks are not higher than other 263 network managed entities, like normal IPv6 addresses managed by DHCP, 264 or addresses logged by ACL. 266 6. IANA Considerations 268 There are no IANA considerations in this document. 270 7. Acknowledgements 272 Useful comments were made by Marcelo Bagnulo and Alberto Garcia, 273 UC3M, Spain and other members of the IETF CSI working group. 275 8. Change Log [RFC Editor please remove] 277 draft-jiang-csi-dhacpv6-cga-ps-00, original version, 2008-10-27 279 draft-jiang-csi-dhacpv6-cga-ps-01, revised after comments at IETF 73, 280 2009-01-08 282 draft-jiang-csi-dhacpv6-cga-ps-02, revised after comments at CSI 283 mailing list, 2009-06-17 285 draft-jiang-csi-dhacpv6-cga-ps-03, revised after comments at CSI 286 mailing list, 2009-09-18 288 draft-ietf-csi-dhacpv6-cga-ps-00, revised after comments at CSI 289 mailing list and wg adoption call, 2009-10-12 291 draft-ietf-csi-dhacpv6-cga-ps-01, revised after comments at IETF 76, 292 2009-12-16 294 draft-ietf-csi-dhacpv6-cga-ps-02, revised after comments received in 295 CSI mail list, 2010-04-23 297 draft-ietf-csi-dhacpv6-cga-ps-03, revised after comments received in 298 CSI mail list, 2010-06-22 300 draft-ietf-csi-dhacpv6-cga-ps-04, revised after comments received in 301 CSI mail list, 2010-09-08 303 9. References 305 9.1. Normative References 307 [RFC3315] R. Droms, Ed., J. Bound, B. Volz, T. Lemon, C. Perkins and 308 M. Carney, "Dynamic Host Configure Protocol for IPv6", RFC 309 3315, July 2003. 311 [RFC3971] J. Arkko, J. Kempf, B. Zill and P. Nikander, "SEcure 312 Neighbor Discovery (SEND)", RFC 3971, March 2005. 314 [RFC3972] T. Aura, "Cryptographically Generated Address", RFC 3972, 315 March 2005. 317 [RFC4862] S. Thomson and T. Narten, "IPv6 Stateless Address 318 Autoconfiguration", RFC 4862, September 2007. 320 [RFC5533] M. Bagnulo and E. Nordmark, "Shim6: Level 3 Multihoming 321 Shim Protocol for IPv6", RFC 5533, June 2009. 323 [RFC5739] P. Eronen, J. Laganier, C. Madson, "IPv6 Configuration in 324 Internet Key Exchange Protocol Version 2 (IKEv2)", 325 RFC 5739, February 2010. 327 Author's Addresses 329 Sheng Jiang 330 Huawei Technologies Co., Ltd 331 KuiKe Building, No.9 Xinxi Rd., 332 Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085 333 P.R. China 334 Phone: 86-10-82836081 335 Email: shengjiang@huawei.com 337 Sean Shen 338 CNNIC 339 4, South 4th Street, Zhongguancun 340 Beijing 100190 341 P.R. China 342 Email: shenshuo@cnnic.cn 344 Tim Chown 345 University of Southampton 346 Highfield 347 Southampton, Hampshire SO17 1BJ 348 United Kingdom 349 Email: tjc@ecs.soton.ac.uk