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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) == Unused Reference: 'RFC2460' is defined on line 291, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) == Outdated reference: A later version (-08) exists of draft-ietf-6man-ipv6-address-generation-privacy-01 == Outdated reference: A later version (-08) exists of draft-ietf-opsec-ipv6-host-scanning-04 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Dynamic Host Configuration (dhc) F. Gont 3 Internet-Draft SI6 Networks / UTN-FRH 4 Intended status: Standards Track W. Liu 5 Expires: April 4, 2015 Huawei Technologies 6 October 1, 2014 8 A Method for Generating Semantically Opaque Interface Identifiers with 9 Dynamic Host Configuration Protocol for IPv6 (DHCPv6) 10 draft-ietf-dhc-stable-privacy-addresses-00 12 Abstract 14 This document specifies a method for selecting IPv6 Interface 15 Identifiers, to be employed by Dynamic Host Configuration Protocol 16 for IPv6 (DHCPv6) servers when leasing non-temporary IPv6 addresses 17 to DHCPv6 clients. This method is a DHCPv6 server side algorithm, 18 that does not require any updates to the existing DHCPv6 19 specifications. The aforementioned method results in stable 20 addresses within each subnet, even in the presence of multiple DHCPv6 21 servers or even DHCPv6 server reinstallments. It is a DHCPv6-variant 22 of the method specified in RFC 7217 for IPv6 Stateless Address 23 Autoconfiguration. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on April 4, 2015. 42 Copyright Notice 44 Copyright (c) 2014 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3. Method Specification . . . . . . . . . . . . . . . . . . . . 3 62 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 63 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 64 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 65 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 66 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 67 7.2. Informative References . . . . . . . . . . . . . . . . . 7 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 70 1. Introduction 72 Stable IPv6 addresses tend to simplify event logging, trouble- 73 shooting, enforcement of access controls and quality of service, etc. 74 However, there are a number of scenarios in which a host employing 75 the DHCPv6 protocol [RFC3315] may be assigned different IPv6 76 addresses for the same interface within the same subnet over time. 77 For example, this may happen when multiple servers operate on the 78 same network to provide increased availability, but may also happen 79 as a result of DHCPv6 server reinstallments and other scenarios. 81 This document specifies a method for selecting IPv6 Interface 82 Identifiers, to be employed by Dynamic Host Configuration Protocol 83 for IPv6 (DHCPv6) servers when leasing non-temporary IPv6 addresses 84 to DHCPv6 clients (i.e., to be employed with IA_NA options). This 85 method is a DHCPv6 server side algorithm, that does not require any 86 updates to the existing DHCPv6 specifications. The aforementioned 87 method has the following properties: 89 o The resulting IPv6 addresses remain stable within each subnet for 90 the same network interface of the same client, even when different 91 DHCPv6 servers (implementing this specification) are employed. 93 o It must be difficult for an outsider to predict the IPv6 addresses 94 that will be generated by the method specified in this document, 95 even with knowledge of the IPv6 addresses generated for other 96 nodes within the same network. 98 The method specified in this document achieves the aforementioned 99 goals by means of a calculated technique as opposed to e.g. state- 100 sharing among DHCPv6 servers . This approach has been already 101 suggested in [RFC7031]. We note that the method specified in this 102 document is essentially a DHCPv6-version of the "Method for 103 Generating Semantically Opaque Interface Identifiers with IPv6 104 Stateless Address Autoconfiguration (SLAAC)" specified in [RFC7217]. 106 2. Terminology 108 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 109 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 110 document are to be interpreted as described in RFC 2119 [RFC2119]. 112 3. Method Specification 114 DHCPv6 server implementations conforming to this specification MUST 115 generate non-temporary IPv6 addresses using the algorithm specified 116 in this section. 118 Implementations conforming to this specification SHOULD provide the 119 means for a system administrator to enable or disable the use of this 120 algorithm for generating IPv6 addresses. 122 Unless otherwise noted, all of the parameters included in the 123 expression below MUST be included when generating an IPv6 address. 125 1. Compute a random (but stable) identifier with the expression: 127 RID = F(Prefix | Client_DUID | IAID | Counter | secret_key) 129 Where: 131 RID: 132 Random (but stable) Identifier 134 F(): 135 A pseudorandom function (PRF) that MUST NOT be computable from 136 the outside (without knowledge of the secret key). F() MUST 137 also be difficult to reverse, such that it resists attempts to 138 obtain the secret_key, even when given samples of the output 139 of F() and knowledge or control of the other input parameters. 140 F() SHOULD produce an output of at least 64 bits. F() could 141 be implemented as a cryptographic hash of the concatenation of 142 each of the function parameters. The default algorithm to be 143 employed for F() SHOULD be SHA-1 [FIPS-SHS]. An 144 implementation MAY provide the means for selecting other other 145 algorithms (e.g., SHA-256) for F(). Note: MD5 [RFC1321] is 146 considered unacceptable for F() [RFC6151]. 148 |: 149 An operator representing "concatenation". 151 Prefix: 152 A prefix that represents an IPv6 address pool from which the 153 DHCPv6 server will assign addresses. That is, this algorithm 154 REQUIRES that the DHCPv6 server manages all the IPv6 address 155 space within a specified prefix (as opposed to, e.g., an 156 address range that cannot be represented with a prefix 157 notation) and that it can be configured with such a prefix. 158 If multiple servers operate on the same network to provide 159 increased availability, all such DHCPv6 servers MUST be 160 configured with the same Prefix. It is the administrator's 161 responsibility that the aforementioned requirement is met. 163 Client_DUID: 164 The DUID value contained in the Client Identifier option 165 received in the client message. 167 IAID: 168 The IAID value contained in the IA_NA option received in the 169 client message. 171 Counter: 172 A variable that is employed to resolve address conflicts. It 173 MUST be initialized to 0. 175 secret_key: 176 A secret key configured by the DHCPv6 server administrator, 177 which MUST NOT be known by the attacker. An implementation of 178 this specification MUST provide an interface for viewing and 179 changing the secret key. All DHCPv6 servers leasing addresses 180 from the same Prefix MUST employ the same secret key. 182 2. The Interface Identifier is obtained by taking as many bits from 183 the RID value (computed in the previous step) as necessary, 184 starting from the least significant bit. 186 We note that [RFC4291] requires that, the Interface IDs of all 187 unicast addresses (except those that start with the binary 188 value 000) be 64-bit long. However, the method discussed in 189 this document could be employed for generating Interface IDs 190 of any arbitrary length, albeit at the expense of reduced 191 entropy (when employing Interface IDs smaller than 64 bits). 193 The resulting Interface Identifier MUST be compared against the 194 reserved IPv6 Interface Identifiers [RFC5453] 195 [IANA-RESERVED-IID]. In the event that an unacceptable 196 identifier has been generated, the Counter variable should be 197 incremented by 1, and a new Interface ID should be computed with 198 the updated Counter value. 200 3. The IPv6 address is finally obtained by concatenating the Prefix 201 with the Interface Identifier obtained in the previous step. If 202 the resulting address is not available (e.g., there is a 203 conflicting binding), the server should increment the Counter 204 variable, and a new Interface ID and IPv6 address should be 205 computed with the updated Counter value. 207 This document requires that SHA-1 be the default function to be used 208 for F(), such that, all other configuration parameters being the 209 same, different implementations of this specification result in the 210 same IPv6 addresses. 212 Including the Prefix in the PRF computation causes the Interface 213 Identifier to for each address from a different prefix assigned to 214 the same client. This mitigates the correlation of activities of 215 multi-homed nodes (since each of the corresponding addresses will 216 employ a different Interface ID), host-tracking (since the network 217 prefix will change as the node moves from one network to another), 218 and any other attacks that benefit from predictable Interface 219 Identifiers (such as IPv6 address scanning attacks) 220 [I-D.ietf-6man-ipv6-address-generation-privacy]. 222 As required by [RFC3315], an IAID is associated with each of the 223 client's network interfaces, and is consistent across restarts of the 224 DHCP client. 226 The Counter parameter provides the means to intentionally cause this 227 algorithm to produce a different IPv6 addresses (all other parameters 228 being the same). This could be necessary to resolve address 229 conflicts (e.g. the resulting address having a conflicting binding). 231 Note that the result of F() in the algorithm above is no more secure 232 than the secret key. If an attacker is aware of the PRF that is 233 being used by the DHCPv6 server (which we should expect), and the 234 attacker can obtain enough material (i.e. addresses generated by the 235 DHCPv6 server), the attacker may simply search the entire secret-key 236 space to find matches. To protect against this, the secret key 237 SHOULD be of at least 128 bits. Key lengths of at least 128 bits 238 should be adequate. 240 Providing a mechanism to display and change the secret_key is crucial 241 for having different DHCPv6 servers produce the same IPv6 addresses, 242 and for causing a replacement system to generate the same IPv6 243 addresses as the system being replaced. We note that since the 244 privacy of the scheme specified in this document relies on the 245 secrecy of the secret_key parameter, implementations should constrain 246 access to the secret_key parameter to the extent practicable (e.g., 247 require superuser privileges to access it). Furthermore, in order to 248 prevent leakages of the secret_key parameter, it should not be used 249 for any other purposes than being a parameter to the scheme specified 250 in this document. 252 We note that all of the bits in the resulting Interface IDs are 253 treated as "opaque" bits [RFC7136]. For example, the universal/local 254 bit of Modified EUI-64 format identifiers is treated as any other bit 255 of such identifier. 257 4. IANA Considerations 259 There are no IANA registries within this document. The RFC-Editor 260 can remove this section before publication of this document as an 261 RFC. 263 5. Security Considerations 265 The method specified in this document results in IPv6 Interface 266 Identifiers (and hence IPv6 addresses) that do not follow any 267 specific pattern. Thus, address-scanning attacks 268 [I-D.ietf-opsec-ipv6-host-scanning] are mitigated. 270 The method specified in this document neither mitigates nor 271 exacerbates the security considerations for DHCPv6 discussed in 272 [RFC3315]. 274 6. Acknowledgements 276 This document is based on [RFC7217], authored by Fernando Gont. 278 The authors would like to thank Tatuya Jinmei for providing valuable 279 comments on earlier versions of this documents. 281 The authors would like to thank Ted Lemon, who kindly answered some 282 DHCPv6-related questions. 284 7. References 286 7.1. Normative References 288 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 289 Requirement Levels", BCP 14, RFC 2119, March 1997. 291 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 292 (IPv6) Specification", RFC 2460, December 1998. 294 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 295 and M. Carney, "Dynamic Host Configuration Protocol for 296 IPv6 (DHCPv6)", RFC 3315, July 2003. 298 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 299 Architecture", RFC 4291, February 2006. 301 [RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers", RFC 302 5453, February 2009. 304 [RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6 305 Interface Identifiers", RFC 7136, February 2014. 307 7.2. Informative References 309 [FIPS-SHS] 310 FIPS, , "Secure Hash Standard (SHS)", Federal Information 311 Processing Standards Publication 180-4, March 2012, 312 . 315 [I-D.ietf-6man-ipv6-address-generation-privacy] 316 Cooper, A., Gont, F., and D. Thaler, "Privacy 317 Considerations for IPv6 Address Generation Mechanisms", 318 draft-ietf-6man-ipv6-address-generation-privacy-01 (work 319 in progress), February 2014. 321 [I-D.ietf-opsec-ipv6-host-scanning] 322 Gont, F. and T. Chown, "Network Reconnaissance in IPv6 323 Networks", draft-ietf-opsec-ipv6-host-scanning-04 (work in 324 progress), June 2014. 326 [IANA-RESERVED-IID] 327 Reserved IPv6 Interface Identifiers, , 328 "http://www.iana.org/assignments/ipv6-interface-ids/ 329 ipv6-interface-ids.xml", . 331 [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, 332 April 1992. 334 [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations 335 for the MD5 Message-Digest and the HMAC-MD5 Algorithms", 336 RFC 6151, March 2011. 338 [RFC7031] Mrugalski, T. and K. Kinnear, "DHCPv6 Failover 339 Requirements", RFC 7031, September 2013. 341 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 342 Interface Identifiers with IPv6 Stateless Address 343 Autoconfiguration (SLAAC)", RFC 7217, April 2014. 345 Authors' Addresses 347 Fernando Gont 348 SI6 Networks / UTN-FRH 349 Evaristo Carriego 2644 350 Haedo, Provincia de Buenos Aires 1706 351 Argentina 353 Phone: +54 11 4650 8472 354 Email: fgont@si6networks.com 355 URI: http://www.si6networks.com 357 Will(Shucheng) Liu 358 Huawei Technologies 359 Bantian, Longgang District 360 Shenzhen 518129 361 P.R. China 363 Email: liushucheng@huawei.com