idnits 2.17.1 draft-ietf-dhc-dhcpv6-privacy-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (December 27, 2015) is 3043 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 2629 (Obsoleted by RFC 7749) -- Obsolete informational reference (is this intentional?): RFC 3633 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 4941 (Obsoleted by RFC 8981) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 dhc S. Krishnan 3 Internet-Draft Ericsson 4 Intended status: Informational T. Mrugalski 5 Expires: June 29, 2016 ISC 6 S. Jiang 7 Huawei Technologies Co., Ltd 8 December 27, 2015 10 Privacy considerations for DHCPv6 11 draft-ietf-dhc-dhcpv6-privacy-02 13 Abstract 15 DHCPv6 is a protocol that is used to provide addressing and 16 configuration information to IPv6 hosts. This document described the 17 privacy issues associated with the use of DHCPv6 by the Internet 18 users. It is intended to be an analysis of the present situation and 19 doe not propose any solutions. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on June 29, 2016. 38 Copyright Notice 40 Copyright (c) 2015 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. DHCPv6 options carrying identifiers . . . . . . . . . . . . . 4 58 3.1. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3.2. Client Identifier Option . . . . . . . . . . . . . . . . 4 60 3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options . . 4 61 3.4. Client FQDN Option . . . . . . . . . . . . . . . . . . . 5 62 3.5. Client Link-layer Address Option . . . . . . . . . . . . 5 63 3.6. Option Request Option . . . . . . . . . . . . . . . . . . 6 64 3.7. Vendor Class and Vendor-specific Information Options . . 6 65 3.8. Civic Location Option . . . . . . . . . . . . . . . . . . 6 66 3.9. Coordinate-Based Location Option . . . . . . . . . . . . 6 67 3.10. Client System Architecture Type Option . . . . . . . . . 7 68 3.11. Relay Agent Options . . . . . . . . . . . . . . . . . . . 7 69 3.11.1. Subscriber ID Option . . . . . . . . . . . . . . . . 7 70 3.11.2. Interface ID Option . . . . . . . . . . . . . . . . 7 71 3.11.3. Remote ID Option . . . . . . . . . . . . . . . . . . 8 72 3.11.4. Relay-ID Option . . . . . . . . . . . . . . . . . . 8 73 4. Existing Mechanisms That Affect Privacy . . . . . . . . . . . 8 74 4.1. Temporary addresses . . . . . . . . . . . . . . . . . . . 8 75 4.2. DNS Updates . . . . . . . . . . . . . . . . . . . . . . . 9 76 4.3. Allocation strategies . . . . . . . . . . . . . . . . . . 9 77 5. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 78 5.1. Device type discovery (fingerprinting) . . . . . . . . . 10 79 5.2. Operating system discovery (fingerprinting) . . . . . . . 11 80 5.3. Finding location information . . . . . . . . . . . . . . 11 81 5.4. Finding previously visited networks . . . . . . . . . . . 11 82 5.5. Finding a stable identity . . . . . . . . . . . . . . . . 11 83 5.6. Pervasive monitoring . . . . . . . . . . . . . . . . . . 12 84 5.7. Finding client's IP address or hostname . . . . . . . . . 12 85 5.8. Correlation of activities over time . . . . . . . . . . . 12 86 5.9. Location tracking . . . . . . . . . . . . . . . . . . . . 12 87 5.10. Leasequery & bulk leasequery . . . . . . . . . . . . . . 13 88 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 89 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13 90 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 91 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 92 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 93 10.1. Normative References . . . . . . . . . . . . . . . . . . 14 94 10.2. Informative References . . . . . . . . . . . . . . . . . 14 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 97 1. Introduction 99 DHCPv6 [RFC3315] is a protocol that is used to provide addressing and 100 configuration information to IPv6 hosts. The DHCPv6 protocol uses 101 several identifiers that could become a source for gleaning 102 information about the IPv6 host. This information may include device 103 type, operating system information, location(s) that the device may 104 have previously visited, etc. This document discusses the various 105 identifiers used by DHCPv6 and the potential privacy issues 106 [RFC6973]. In particular, it also takes into consideration the 107 problem of pervasive monitoring [RFC7258]. 109 Future works may propose protocol changes to fix the privacy issues 110 that have been analyzed in this document. Protocol changes are out 111 of scope for this document. 113 The primary focus of this document is around privacy considerations 114 for clients to support client mobility and connection to random 115 networks. The privacy of DHCP servers and relay agents are 116 considered less important as they are typically open for public 117 services. And, it is generally assumed that relay agent to server 118 communication is protected from casual snooping, as that 119 communication occurs in the provider's backbone. Nevertheless, the 120 topics involving relay agents and servers are explored to some 121 degree. However, future work may want to further explore privacy of 122 DHCP servers and relay agents. 124 2. Terminology 126 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 127 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 128 document are to be interpreted as described in [RFC2119]. When these 129 words are not in ALL CAPS (such as "should" or "Should"), they have 130 their usual English meanings, and are not to be interpreted as 131 [RFC2119] key words. 133 Naming convention from [RFC3315] and related is used throughout this 134 document. In addition the following terminology is used: 136 Stable identifier - Any property disclosed by a DHCP client that 137 does not change over time or changes very infrequently and is 138 unique for said client in a given context. Examples may 139 include MAC address, client-id or a hostname. Some 140 identifiers may be considered stable only under certain 141 conditions, for example one client implementation may keep 142 its client-id stored in stable storage while other may 143 generate it on the fly and use a different one after each 144 boot. Stable identifier may or may not be globally unique. 146 3. DHCPv6 options carrying identifiers 148 In DHCPv6, there are many options which include identification 149 information or can be used to extract the identification information 150 about the client. This section enumerates various options and 151 identifiers conveyed in them, which can be used to disclose client 152 identification. 154 3.1. DUID 156 Each DHCPv6 client and server has a DHCPv6 Unique Identifier (DUID) 157 [RFC3315]. The DUID is designed to be unique across all DHCPv6 158 clients and servers, and to remain stable after it has been initially 159 generated. The DUID can be of different forms. Commonly used forms 160 are based on the link-layer address of one of the device's network 161 interfaces (with or without a timestamp), on the Universally Unique 162 IDentifier (UUID) [RFC6355]. The default type, defined in 163 Section 9.2 of [RFC3315] is DUID-LLT that is based on link-layer 164 address. It is commonly implemented in most popular clients. 166 It is important to understand DUID lifecycle. Clients and servers 167 are expected to generate their DUID once (during first operation) and 168 store it in a non-volatile storage or use the same deterministic 169 algorithm to generate the same DUID value again. This means that 170 most implementations will use the available link-layer address during 171 its first boot. Even if the administrator enables link-layer address 172 randomization, it is likely that it was disabled during the first 173 device boot. Hence the original, unobfuscated link-layer address 174 will likely end up being announced as client DUID, even if the link- 175 layer address has changed (or even if being changed on a periodic 176 basis). The exposure of the original link-layer address in DUID will 177 also undermine other privacy extensions such as [RFC4941]. 179 3.2. Client Identifier Option 181 The Client Identifier Option (OPTION_CLIENTID) [RFC3315] is used to 182 carry the DUID of a DHCPv6 client between a client and a server. 183 There is an analogous Server Identifier Option but it is not as 184 interesting in the privacy context (unless a host can be convinced to 185 start acting as a server). See Section 3.1 for relevant discussion 186 about DUIDs. 188 3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options 190 The Identity Association for Non-temporary Addresses (IA_NA) option 191 [RFC3315] is used to carry the parameters and any non-temporary 192 addresses associated with the given IA_NA. The Identity Association 193 for Temporary Addresses (IA_TA) option [RFC3315] is analogous to the 194 IA_NA option but for temporary addresses. The IA Address option 195 [RFC3315] is used to specify IPv6 addresses associated with an IA_NA 196 or an IA_TA and is encapsulated within the Options field of such an 197 IA_NA or IA_TA option. The Identity Association for Prefix 198 Delegation (IA_PD) [RFC3633] option is used to carry the prefixes 199 that are assigned to the requesting router. IA Prefix option 200 [RFC3633] is used to specify IPv6 prefixes associated with an IA_PD 201 and is encapsulated within the Options field of such an IA_PD option. 203 To differentiate between instances of the same type of IA containers 204 for a client, each IA_NA, IA_TA and IA_PD options have an IAID field 205 with a unique value for a given IA type. It is up to the client to 206 pick unique IAID values. At least one popular implementation uses 207 last four octets of the link-layer address. In most cases, that 208 means that merely two bytes are missing for a full link-layer address 209 reconstruction. However, the first three octets in a typical link- 210 layer address are vendor identifier. That can be determined with 211 high level of certainty using other means, thus allowing full link- 212 layer address discovery. 214 3.4. Client FQDN Option 216 The Client Fully Qualified Domain Name (FQDN) option [RFC4704] is 217 used by DHCPv6 clients and servers to exchange information about the 218 client's fully qualified domain name and about who has the 219 responsibility for updating the DNS with the associated AAAA and PTR 220 RRs. 222 A client can use this option to convey all or part of its domain name 223 to a DHCPv6 server for the IPv6-address-to-FQDN mapping. In most 224 case a client sends its hostname as a hint for the server. The 225 DHCPv6 server MAY be configured to modify the supplied name or to 226 substitute a different name. The server should send its notion of 227 the complete FQDN for the client in the Domain Name field. 229 3.5. Client Link-layer Address Option 231 The Client link-layer address option [RFC6939] is used by first-hop 232 DHCPv6 relays to provide the client's link-layer address towards the 233 server. 235 DHCPv6 relay agents that receive messages originating from clients 236 may include the link-layer source address of the received DHCPv6 237 message in the Client Link-Layer Address option, in relayed DHCPv6 238 Relay-Forward messages. 240 3.6. Option Request Option 242 DHCPv6 clients include an Option Request option [RFC3315] in DHCPv6 243 messages to inform the server about options the client wants the 244 server to send to the client. 246 The content of an Option Request option are the option codes for an 247 option requested by the client. The client may additionally include 248 instances of those options that are identified in the Option Request 249 option, with data values as hints to the server about parameter 250 values the client would like to have returned. 252 3.7. Vendor Class and Vendor-specific Information Options 254 The Vendor Class option, defined in Section 22.16 of [RFC3315] is 255 used by a DHCPv6 client to identify the vendor that manufactured the 256 hardware on which the client is running. 258 The Vendor-specific Information Option, defined in Section 22.17 of 259 [RFC3315] includes enterprise number, which identifies the client's 260 vendor and often includes a number of additional parameters that are 261 specific to a given vendor. That may include any type of information 262 the vendor deems useful. It should be noted that this information 263 may be present (and different) in both directions: client to server 264 and server to client communications. 266 The information contained in the data area of this option is 267 contained in one or more opaque fields that identify details of the 268 hardware configuration, for example, the version of the operating 269 system the client is running or the amount of memory installed on the 270 client. 272 3.8. Civic Location Option 274 DHCPv6 servers use the Civic Location option [RFC4776] to deliver the 275 location information (the civic and postal addresses) from the DHCPv6 276 server to the DHCPv6 clients. It may refer to three locations: the 277 location of the DHCPv6 server, the location of the network element 278 believed to be closest to the client, or the location of the client, 279 identified by the "what" element within the option. 281 3.9. Coordinate-Based Location Option 283 The GeoLoc options [RFC6225] is used by DHCPv6 server to provide the 284 coordinate- based geographic location information to the DHCPv6 285 clients. It enable a DHCPv6 client to obtain its location. 287 3.10. Client System Architecture Type Option 289 The Client System Architecture Type option [RFC5970] is used by 290 DHCPv6 client to send a list of supported architecture types to the 291 DHCPv6 server. It is used by clients that must be booted using the 292 network rather than from local storage, so the server can decide 293 which boot file should be provided to the client. 295 3.11. Relay Agent Options 297 A DHCPv6 relay agent may include a number of options. Those option 298 contain information that can be used to identify the client. Those 299 options are almost exclusively exchanged between the relay agent and 300 the server, thus never leaving the operators network. In particular, 301 they're almost never present in the last wireless hop in case of WiFi 302 networks. The only exception to that rule is somewhat infrequently 303 used Relay Supplied Options option [RFC6422]. This fact implies that 304 the threat model related relay options is slightly different. 305 Traffic sniffing at the last hop and related class of attacks 306 typically do not apply. On the other hand, all attacks that involve 307 operator's intfrastructure (either willing or coerced cooperation or 308 infrastructure being compromised) usually apply. 310 The following subsections describe various options inserted by the 311 relay agents. 313 3.11.1. Subscriber ID Option 315 A DHCPv6 relay may include a Subscriber ID option [RFC4580] to 316 associate some provider-specific information with clients' DHCPv6 317 messages that is independent of the physical network configuration. 319 In many deployments, the relay agent that inserts this option is 320 configured to use client's link-layer address as Subscriber ID. 322 3.11.2. Interface ID Option 324 A DHCPv6 relay includes the Interface ID [RFC3315] option to identify 325 the interface on which it received the client message that is being 326 relayed. 328 Although in principle Interface ID can be arbitrarily long with 329 completely random values, it is sometimes a text string that includes 330 the relay agent name followed by interface name. This can be used 331 for fingerprinting the relay or determining client's point of 332 attachment. 334 3.11.3. Remote ID Option 336 A DHCPv6 relay includes a Remote ID option [RFC4649] to identify the 337 remote host end of the circuit. 339 The remote-id is vendor specific, for which the vendor is indicated 340 in the enterprise-number field. The remote-id field may encode the 341 information that identified the DHCPv6 clients: 343 o a "caller ID" telephone number for dial-up connection 345 o a "user name" prompted for by a Remote Access Server 347 o a remote caller ATM address o a "modem ID" of a cable data modem 349 o the remote IP address of a point-to-point link 351 o an interface or port identifier 353 3.11.4. Relay-ID Option 355 Relay agent may include Relay-ID [RFC5460], which contains a unique 356 relay agent identifier. While its intended use is to provide 357 additional information for the server, so it would be able to respond 358 to leasequeries later, this information can be also used to identify 359 client's location within the network. 361 4. Existing Mechanisms That Affect Privacy 363 This section describes deployed DHCPv6 mechanisms that can affect 364 privacy. 366 4.1. Temporary addresses 368 [RFC3315] defines a mechanism for a client to request temporary 369 addresses. The idea behind temporary addresses is that a client can 370 request a temporary address for a specific purpose, use it, and then 371 never renew it. i.e. let it expire. 373 There are a number of serious issues, both related to protocol and 374 its implementations, that make temporary addresses nearly useless for 375 their original goal. First, [RFC3315] does not include T1 and T2 376 renewal timers in IA_TA (a container for temporary addresses). 377 However, in section 18.1.3 it explicitly mentions that temporary 378 addresses can be renewed. Client implementations may mistakenly 379 renew temporary addresses if they are not careful (i.e., by including 380 the IA_TA with the same IAID in Renew or Rebind requests, rather than 381 a new IAID - see [RFC3315] Section 22.5), thus forfeiting short 382 liveness. [RFC4704] does not explicitly prohibit servers to update 383 DNS for assigned temporary addresses and there are implementations 384 that can be configured to do that. However, this is not advised as 385 publishing a client's IPv6 address in DNS that is publicly available 386 is a major privacy breach. 388 4.2. DNS Updates 390 The Client FQDN Option[RFC4704] used along with DNS Update [RFC2136] 391 defines a mechanism that allows both clients and server to insert 392 into the DNS domain information about clients. Both forward (AAAA) 393 and reverse (PTR) resource records can be updated. This allows other 394 nodes to conveniently refer to a host, despite the fact that its IPv6 395 address may be changing. 397 This mechanism exposes two important pieces of information: current 398 address (which can be mapped to current location) and client's 399 hostname. The stable hostname can then by used to correlate the 400 client across different network attachments even when its IPv6 401 address keeps changing. 403 4.3. Allocation strategies 405 A DHCPv6 server running in typical, stateful mode is given a task of 406 managing one or more pools of IPv6 resources (currently non-temporary 407 addresses, temporary addresses and/or prefixes, but more resource 408 types may be defined in the future). When a client requests a 409 resource, server must pick a resource out of configured pool. 410 Depending on the server's implementation, various allocation 411 strategies are possible. Choices in this regard may have privacy 412 implications. 414 Iterative allocation - a server may choose to allocate addresses one 415 by one. That strategy has the benefit of being very fast, thus can 416 be favored in deployments that prefer performance. However, it makes 417 the resources very predictable. Also, since the resources allocated 418 tend to be clustered at the beginning of available pool, it makes 419 scanning attacks much easier. 421 Identifier-based allocation - some server implementations use a fixed 422 identifier for a specific client, seemingly taken from the client's 423 MAC address when available or some lower bits of client's source IPv6 424 address. This has a property of being convenient for converting IP 425 address to/from other identifiers, especially if the identifier is or 426 contains MAC address. It is also convenient, as returning client is 427 very likely to get the same address, even if the server does not 428 retain previous client's address. Those properties are convenient 429 for system administrators, so DHCPv6 server implementors are 430 sometimes requested to implement it. There is at least one 431 implementation that supports it. The downside of such allocation is 432 that the client now discloses its identifier in its IPv6 address to 433 all services it connects to. That means that correlation of 434 activities over time, location tracking, address scanning and OS/ 435 vendor discovery apply. 437 Hash allocation - it's an extension of identifier based allocation. 438 Instead of using the identifier directly, it is being hashed first. 439 If the hash is implemented correctly, it removes the flaw of 440 disclosing the identifier, a property that eliminates susceptibility 441 to address scanning and OS/vendor discovery. If the hash is poorly 442 implemented (e.g. can be reverted), it introduces no improvement over 443 identifier-based allocation. 445 Random allocation - a server can pick a resource randomly out of 446 available pool. That strategy works well in scenarios where pool 447 utilization is small, as the likelihood of collision (resulting in 448 the server needing to repeat randomization) is small. With the pool 449 allocation increasing, the collision is disproportionally large, due 450 to birthday paradox. With high pool utilization (e.g. when 90% of 451 available resources being allocated already), the server will use 452 most computational resources to repeatedly pick a random resource, 453 which will degrade its performance. This allocation scheme 454 essentially prevents returning clients from getting the same address 455 or prefix again. On the other hand, it is beneficial from privacy 456 perspective as addresses and prefixes generated that way are not 457 susceptible to correlation attacks, OS/vendor discovery attacks or 458 identity discovery attacks. Note that even though the address or 459 prefix itself may be resilient to a given attack, the client may 460 still be susceptible if additional information is disclosed other 461 way, e.g. client's address can be randomized, but it still can leak 462 its MAC address in client-id option. 464 Other allocation strategies may be implemented. 466 5. Attacks 468 5.1. Device type discovery (fingerprinting) 470 The type of device used by the client can be guessed by the attacker 471 using the Vendor Class option, Vendor-specific Information option, 472 the Client Link-layer Address option, and by parsing the Client ID 473 option. All of those options may contain OUI (Organizationally 474 Unique Identifier) that represents the device's vendor. That 475 knowledge can be used for device-specific vulnerability exploitation 476 attacks. See Section 3.4 of 478 [I-D.ietf-6man-ipv6-address-generation-privacy] for a discussion 479 about this type of attack. 481 5.2. Operating system discovery (fingerprinting) 483 The operating system running on a client can be guessed using the 484 Vendor Class option, the Vendor-specific Information option, the 485 Client System Architecture Type option, or by using fingerprinting 486 techniques on the combination of options requested using the Option 487 Request option. See Section 3.4 of 488 [I-D.ietf-6man-ipv6-address-generation-privacy] for a discussion 489 about this type of attack. 491 5.3. Finding location information 493 The location information can be obtained by the attacker by many 494 means. The most direct way to obtain this information is by looking 495 into a message originating from the server server that contains the 496 Civic Location or GeoLoc option. It can also be indirectly inferred 497 using the Remote ID Option, the Interface ID option (e.g. if an 498 access circuit on an Access Node corresponds to a civic location), or 499 the Subscriber ID Option (if the attacker has access to subscriber 500 info). 502 5.4. Finding previously visited networks 504 When DHCPv6 clients connect to a network, they attempt to obtain the 505 same address they had used before they attached to the network. They 506 do this by putting the previously assigned address(es) in the IA 507 Address Option(s). [RFC3315] does not exclude IA_TA in such a case, 508 so it is possible that a client implementation includes an address 509 contained in an IA_TA for the Confirm message. By observing these 510 addresses, an attacker can identify the network the client had 511 previously visited. 513 5.5. Finding a stable identity 515 An attacker might use a stable identity gleaned from DHCPv6 messages 516 to correlate activities of a given client on unrelated networks. The 517 Client FQDN option, the Subscriber ID Option and the Client ID 518 options can serve as long lived identifiers of DHCPv6 clients. The 519 Client FQDN option can also provide an identity that can easily be 520 correlated with web server activity logs. 522 5.6. Pervasive monitoring 524 This is an enhancement, or a combination of most aforementioned 525 mechanisms. Operator (or anyone who has access to its data), who 526 controls non-trivial number of access points or network segments, may 527 use obtained information about a single client and observer client's 528 habits. 530 5.7. Finding client's IP address or hostname 532 Many DHCPv6 deployments use DNS Updates [RFC4704] that put client's 533 information (current IP address, client's hostname) into DNS, where 534 it is easily accessible by anyone interested. Client ID is also 535 disclosed, albeit in not easily accessible form (SHA-256 digest of 536 the client-id). As SHA-256 is considered irreversible, DHCID can't 537 be converted back to client-id. However, SHA-256 digest can be used 538 as an unique identifier that is accessible by any host. 540 5.8. Correlation of activities over time 542 As with other identifiers, an IPv6 address can be used to correlate 543 the activities of a host for at least as long as the lifetime of the 544 address. If that address was generated from some other, stable 545 identifier and that generation scheme can be deducted by an attacker, 546 the duration of correlation attack extends to that identifier. In 547 many cases, its lifetime is equal to the lifetime of the device 548 itself. See Section 3.1 of 549 [I-D.ietf-6man-ipv6-address-generation-privacy] for detailed 550 discussion. 552 5.9. Location tracking 554 If a stable identifier is used for assigning an address and such 555 mapping is discovered by an attacker (e.g. a server that uses IEEE- 556 identifier-based IID to generate IPv6 address), all scenarios 557 discussed in Section 3.2 of 558 [I-D.ietf-6man-ipv6-address-generation-privacy] apply. In particular 559 both passive (a service that the client connects to can log client's 560 address and draw conclusions regarding its location and movement 561 patterns based on prefix it is connecting from) and active (attacker 562 can send ICMPv6 echo requests or other probe packets to networks of 563 suspected client locations) can be used. To give specific example, 564 by accessing a social portal from tomek- 565 laptop.coffee.somecity.com.example, tomek- 566 laptop.mycompany.com.example and tomek-laptop.myisp.example.com, the 567 portal administrator can draw conclusions about tomek-laptop's owner 568 current location and his habits. 570 5.10. Leasequery & bulk leasequery 572 Attackers may pretend as an access concentrator, either DHCPv6 relay 573 agent or DHCPv6 client, to obtain location information directly from 574 the DHCP server(s) using the DHCPv6 Leasequery [RFC5007] mechanism. 576 Location information is information needed by the access concentrator 577 to forward traffic to a broadband-accessible host. This information 578 includes knowledge of the host hardware address, the port or virtual 579 circuit that leads to the host, and/or the hardware address of the 580 intervening subscriber modem. 582 Furthermore, the attackers may use DHCPv6 bulk leasequery [RFC5460] 583 mechanism to obtain bulk information about DHCPv6 bindings, even 584 without knowing the target bindings. 586 Additionally, active leasequery [RFC7653] is a mechanism for 587 subscribing to DHCPv6 lease update changes in near real-time. The 588 intent of this mechanism is to update operator's database, but if 589 misused, an attacker could defeat server's authentication mechanisms 590 and subscribe to all updates. He then could continue receiving 591 updates, without any need for local presence. 593 6. Security Considerations 595 In current practice, the client privacy and the client authentication 596 are mutually exclusive. The client authentication procedure reveals 597 additional client information in their certificates/identifiers. 598 Full privacy for the clients may mean the clients are also anonymous 599 for the server and the network. 601 7. Privacy Considerations 603 This document at its entirety discusses privacy considerations in 604 DHCPv6. As such, no dedicated discussion is needed. 606 8. IANA Considerations 608 This draft does not request any IANA action. 610 9. Acknowledgements 612 The authors would like to thank Stephen Farrell, Ted Lemon, Ines 613 Robles, Russ White, Christian Schaefer, Jinmei Tatuya, Bernie Volz, 614 Marcin Siodelski, Christian Huitema and other members of DHC WG for 615 their valuable comments. 617 This document was produced using the xml2rfc tool [RFC2629]. 619 10. References 621 10.1. Normative References 623 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 624 Requirement Levels", BCP 14, RFC 2119, 625 DOI 10.17487/RFC2119, March 1997, 626 . 628 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 629 C., and M. Carney, "Dynamic Host Configuration Protocol 630 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 631 2003, . 633 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 634 Morris, J., Hansen, M., and R. Smith, "Privacy 635 Considerations for Internet Protocols", RFC 6973, 636 DOI 10.17487/RFC6973, July 2013, 637 . 639 [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an 640 Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 641 2014, . 643 10.2. Informative References 645 [I-D.ietf-6man-ipv6-address-generation-privacy] 646 Cooper, A., Gont, F., and D. Thaler, "Privacy 647 Considerations for IPv6 Address Generation Mechanisms", 648 draft-ietf-6man-ipv6-address-generation-privacy-08 (work 649 in progress), September 2015. 651 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 652 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 653 RFC 2136, DOI 10.17487/RFC2136, April 1997, 654 . 656 [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, 657 DOI 10.17487/RFC2629, June 1999, 658 . 660 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 661 Host Configuration Protocol (DHCP) version 6", RFC 3633, 662 DOI 10.17487/RFC3633, December 2003, 663 . 665 [RFC4580] Volz, B., "Dynamic Host Configuration Protocol for IPv6 666 (DHCPv6) Relay Agent Subscriber-ID Option", RFC 4580, 667 DOI 10.17487/RFC4580, June 2006, 668 . 670 [RFC4649] Volz, B., "Dynamic Host Configuration Protocol for IPv6 671 (DHCPv6) Relay Agent Remote-ID Option", RFC 4649, 672 DOI 10.17487/RFC4649, August 2006, 673 . 675 [RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for 676 IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN) 677 Option", RFC 4704, DOI 10.17487/RFC4704, October 2006, 678 . 680 [RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol 681 (DHCPv4 and DHCPv6) Option for Civic Addresses 682 Configuration Information", RFC 4776, 683 DOI 10.17487/RFC4776, November 2006, 684 . 686 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 687 Extensions for Stateless Address Autoconfiguration in 688 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 689 . 691 [RFC5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng, 692 "DHCPv6 Leasequery", RFC 5007, DOI 10.17487/RFC5007, 693 September 2007, . 695 [RFC5460] Stapp, M., "DHCPv6 Bulk Leasequery", RFC 5460, 696 DOI 10.17487/RFC5460, February 2009, 697 . 699 [RFC5970] Huth, T., Freimann, J., Zimmer, V., and D. Thaler, "DHCPv6 700 Options for Network Boot", RFC 5970, DOI 10.17487/RFC5970, 701 September 2010, . 703 [RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, Ed., 704 "Dynamic Host Configuration Protocol Options for 705 Coordinate-Based Location Configuration Information", 706 RFC 6225, DOI 10.17487/RFC6225, July 2011, 707 . 709 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 710 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 711 DOI 10.17487/RFC6355, August 2011, 712 . 714 [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", 715 RFC 6422, DOI 10.17487/RFC6422, December 2011, 716 . 718 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 719 Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939, 720 May 2013, . 722 [RFC7653] Raghuvanshi, D., Kinnear, K., and D. Kukrety, "DHCPv6 723 Active Leasequery", RFC 7653, DOI 10.17487/RFC7653, 724 October 2015, . 726 Authors' Addresses 728 Suresh Krishnan 729 Ericsson 730 8400 Decarie Blvd. 731 Town of Mount Royal, QC 732 Canada 734 Phone: +1 514 345 7900 x42871 735 Email: suresh.krishnan@ericsson.com 737 Tomek Mrugalski 738 Internet Systems Consortium, Inc. 739 950 Charter Street 740 Redwood City, CA 94063 741 USA 743 Email: tomasz.mrugalski@gmail.com 745 Sheng Jiang 746 Huawei Technologies Co., Ltd 747 Q14, Huawei Campus, No.156 BeiQing Road 748 Hai-Dian District, Beijing 100095 749 P.R. China 751 Email: jiangsheng@huawei.com