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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 272, 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reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) == Outdated reference: A later version (-08) exists of draft-ietf-6man-ipv6-address-generation-privacy-01 == Outdated reference: A later version (-08) exists of draft-ietf-opsec-ipv6-host-scanning-04 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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: March 9, 2015 Huawei Technologies 6 September 5, 2014 8 A Method for Generating Semantically Opaque Interface Identifiers with 9 Dynamic Host Configuration Protocol for IPv6 (DHCPv6) 10 draft-gont-dhc-stable-privacy-addresses-00 12 Abstract 14 This document specifies a method for generating IPv6 Interface 15 Identifiers to be used by Dynamic Host Configuration Protocol for 16 IPv6 (DHCPv6) servers. This method results in stable addresses 17 within each subnet, even in the presence of multiple DHCPv6 servers 18 or even DHCPv6 server reinstallments. This method is a 19 DHCPv6-variant of the method specified in RFC 7217 for IPv6 Stateless 20 Address Autoconfiguration. 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 March 9, 2015. 39 Copyright Notice 41 Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. Method Specification . . . . . . . . . . . . . . . . . . . . 3 59 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 60 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 61 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 62 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 64 7.2. Informative References . . . . . . . . . . . . . . . . . 7 65 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 67 1. Introduction 69 Stable IPv6 addresses tend to simplify event logging, trouble- 70 shooting, enforcement of access controls and quality of service, etc. 71 However, there are a number of scenarios in which a host employing 72 the DHCPv6 protocol [RFC3315] may be assigned different IPv6 73 addresses for the same interface within the same subnet over time. 74 For example, this may happen when multiple servers operate on the 75 same network to provide increased availability, but may also happen 76 as a result of DHCPv6 server reinstallments and other scenarios. 78 This document specifies a method to be employed by DHCPv6 servers for 79 generating IPv6 addresses, with the following properties: 81 o The resulting IPv6 addresses remain stable within each subnet for 82 the same network interface of the same client, even when different 83 DHCPv6 servers (implementing this specification) are employed. 85 o It must be difficult for an outsider to predict the IPv6 addresses 86 that will be generated by the method specified in this document, 87 even with knowledge of the IPv6 addresses generated for other 88 nodes within the same network. 90 The method specified in this document achieves the aforementioned 91 goals by means of a calculated technique as opposed to e.g. state- 92 sharing among DHCPv6 servers . This approach has been already 93 suggested in [RFC7031]. We note that the method specified in this 94 document is essentially a DHCPv6-version of the "Method for 95 Generating Semantically Opaque Interface Identifiers with IPv6 96 Stateless Address Autoconfiguration (SLAAC)" specified in [RFC7217]. 98 2. Terminology 100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 102 document are to be interpreted as described in RFC 2119 [RFC2119]. 104 3. Method Specification 106 DHCPv6 server implementations conforming to this specification MUST 107 generate non-temporary IPv6 addresses using the algorithm specified 108 in this section. 110 Implementations conforming to this specification SHOULD provide the 111 means for a system administrator to enable or disable the use of this 112 algorithm for generating IPv6 addresses. 114 Unless otherwise noted, all of the parameters included in the 115 expression below MUST be included when generating an IPv6 address. 117 1. Compute a random (but stable) identifier with the expression: 119 RID = F(Prefix | Client_DUID | IA_NA | Counter | secret_key) 121 Where: 123 RID: 124 Random (but stable) Identifier 126 F(): 127 A pseudorandom function (PRF) that MUST NOT be computable from 128 the outside (without knowledge of the secret key). F() MUST 129 also be difficult to reverse, such that it resists attempts to 130 obtain the secret_key, even when given samples of the output 131 of F() and knowledge or control of the other input parameters. 132 F() SHOULD produce an output of at least 64 bits. F() could 133 be implemented as a cryptographic hash of the concatenation of 134 each of the function parameters. The default algorithm to be 135 employed for F() SHOULD be SHA-1 [FIPS-SHS]. An 136 implementation MAY provide the means for selecting other other 137 algorithms (e.g., SHA-256) for F(). Note: MD5 [RFC1321] is 138 considered unacceptable for F() [RFC6151]. 140 |: 141 An operator representing "concatenation". 143 Prefix: 144 The prefix from which the DHCPv6 is assigning addresses (i.e., 145 the prefix representing the address pool). 147 Client_DUID: 148 The DUID value contained in the Client Identifier option 149 received in the client message. 151 IAID: 152 The IAID value contained in the IA_NA option received in the 153 client message. 155 Counter: 156 A variable that is employed to resolve address conflicts. It 157 MUST be initialized to 0. 159 secret_key: 160 A secret key configured by the DHCPv6 server administrator, 161 which MUST NOT be known by the attacker. An implementation of 162 this specification MUST provide an interface for viewing and 163 changing the secret key. All DHCPv6 servers leasing addresses 164 from the same Prefix MUST employ the same secret key. 166 2. The Interface Identifier is obtained by taking as many bits from 167 the RID value (computed in the previous step) as necessary, 168 starting from the least significant bit. 170 We note that [RFC4291] requires that, the Interface IDs of all 171 unicast addresses (except those that start with the binary 172 value 000) be 64-bit long. However, the method discussed in 173 this document could be employed for generating Interface IDs 174 of any arbitrary length, albeit at the expense of reduced 175 entropy (when employing Interface IDs smaller than 64 bits). 177 The resulting Interface Identifier MUST be compared against the 178 reserved IPv6 Interface Identifiers [RFC5453] 179 [IANA-RESERVED-IID]. In the event that an unacceptable 180 identifier has been generated, the Counter variable should be 181 incremented by 1, and a new Interface ID should be computed with 182 the updated Counter value. 184 3. The IPv6 address is finally obtained by concatenating the Prefix 185 with the Interface Identifier obtained in the previous step. If 186 the resulting address is not available (e.g., there is a 187 conflicting binding), the server should increment the Counter 188 variable, and a new Interface ID and IPv6 address should be 189 computed with the updated Counter value. 191 This document requires that SHA-1 be the default function to be used 192 for F(), such that, all other configuration parameters being the 193 same, different implementations of this specification result in the 194 same IPv6 addresses. 196 Including the Prefix in the PRF computation causes the Interface 197 Identifier to for each address from a different prefix assigned to 198 the same client. This mitigates the correlation of activities of 199 multi-homed nodes (since each of the corresponding addresses will 200 employ a different Interface ID), host-tracking (since the network 201 prefix will change as the node moves from one network to another), 202 and any other attacks that benefit from predictable Interface 203 Identifiers (such as IPv6 address scanning attacks) 204 [I-D.ietf-6man-ipv6-address-generation-privacy]. 206 As required by [RFC3315], an IAID is associated with each of the 207 client's network interfaces, and is consistent across restarts of the 208 DHCP client. 210 The Counter parameter provides the means to intentionally cause this 211 algorithm to produce a different IPv6 addresses (all other parameters 212 being the same). This could be necessary to resolve address 213 conflicts (e.g. the resulting address having a conflicting binding). 215 Note that the result of F() in the algorithm above is no more secure 216 than the secret key. If an attacker is aware of the PRF that is 217 being used by the DHCPv6 server (which we should expect), and the 218 attacker can obtain enough material (i.e. addresses generated by the 219 DHCPv6 server), the attacker may simply search the entire secret-key 220 space to find matches. To protect against this, the secret key 221 SHOULD be of at least 128 bits. Key lengths of at least 128 bits 222 should be adequate. 224 Providing a mechanism to display and change the secret_key is crucial 225 for having different DHCPv6 servers produce the same IPv6 addresses, 226 and for causing a replacement system to generate the same IPv6 227 addresses as the system being replaced. We note that since the 228 privacy of the scheme specified in this document relies on the 229 secrecy of the secret_key parameter, implementations should constrain 230 access to the secret_key parameter to the extent practicable (e.g., 231 require superuser privileges to access it). Furthermore, in order to 232 prevent leakages of the secret_key parameter, it should not be used 233 for any other purposes than being a parameter to the scheme specified 234 in this document. 236 We note that all of the bits in the resulting Interface IDs are 237 treated as "opaque" bits [RFC7136]. For example, the universal/local 238 bit of Modified EUI-64 format identifiers is treated as any other bit 239 of such identifier. 241 4. IANA Considerations 243 There are no IANA registries within this document. The RFC-Editor 244 can remove this section before publication of this document as an 245 RFC. 247 5. Security Considerations 249 The method specified in this document results in IPv6 Interface 250 Identifiers (and hence IPv6 addresses) that do not follow any 251 specific pattern. Thus, address-scanning attacks 252 [I-D.ietf-opsec-ipv6-host-scanning] are mitigated. 254 The method specified in this document neither mitigates nor 255 exacerbates the security considerations for DHCPv6 discussed in 256 [RFC3315]. 258 6. Acknowledgements 260 This document is based on [RFC7217], authored by Fernando Gont. 262 The authors would like to thank Ted Lemon, who kindly answered some 263 DHCPv6-related questions. 265 7. References 267 7.1. Normative References 269 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 270 Requirement Levels", BCP 14, RFC 2119, March 1997. 272 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 273 (IPv6) Specification", RFC 2460, December 1998. 275 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 276 and M. Carney, "Dynamic Host Configuration Protocol for 277 IPv6 (DHCPv6)", RFC 3315, July 2003. 279 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 280 Architecture", RFC 4291, February 2006. 282 [RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers", RFC 283 5453, February 2009. 285 [RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6 286 Interface Identifiers", RFC 7136, February 2014. 288 7.2. Informative References 290 [FIPS-SHS] 291 FIPS, , "Secure Hash Standard (SHS)", Federal Information 292 Processing Standards Publication 180-4, March 2012, 293 . 296 [I-D.ietf-6man-ipv6-address-generation-privacy] 297 Cooper, A., Gont, F., and D. Thaler, "Privacy 298 Considerations for IPv6 Address Generation Mechanisms", 299 draft-ietf-6man-ipv6-address-generation-privacy-01 (work 300 in progress), February 2014. 302 [I-D.ietf-opsec-ipv6-host-scanning] 303 Gont, F. and T. Chown, "Network Reconnaissance in IPv6 304 Networks", draft-ietf-opsec-ipv6-host-scanning-04 (work in 305 progress), June 2014. 307 [IANA-RESERVED-IID] 308 Reserved IPv6 Interface Identifiers, , 309 "http://www.iana.org/assignments/ipv6-interface-ids/ 310 ipv6-interface-ids.xml", . 312 [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, 313 April 1992. 315 [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations 316 for the MD5 Message-Digest and the HMAC-MD5 Algorithms", 317 RFC 6151, March 2011. 319 [RFC7031] Mrugalski, T. and K. Kinnear, "DHCPv6 Failover 320 Requirements", RFC 7031, September 2013. 322 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 323 Interface Identifiers with IPv6 Stateless Address 324 Autoconfiguration (SLAAC)", RFC 7217, April 2014. 326 Authors' Addresses 327 Fernando Gont 328 SI6 Networks / UTN-FRH 329 Evaristo Carriego 2644 330 Haedo, Provincia de Buenos Aires 1706 331 Argentina 333 Phone: +54 11 4650 8472 334 Email: fgont@si6networks.com 335 URI: http://www.si6networks.com 337 Will(Shucheng) Liu 338 Huawei Technologies 339 Bantian, Longgang District 340 Shenzhen 518129 341 P.R. China 343 Email: liushucheng@huawei.com