idnits 2.17.1 draft-ietf-dhc-dhcpv6-privacy-03.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 (January 20, 2016) is 3019 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: July 23, 2016 ISC 6 S. Jiang 7 Huawei Technologies Co., Ltd 8 January 20, 2016 10 Privacy considerations for DHCPv6 11 draft-ietf-dhc-dhcpv6-privacy-03 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 July 23, 2016. 38 Copyright Notice 40 Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . . . 12 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. The attacks that are enabled by such disclosures are 153 detailed in Section 5. 155 3.1. DUID 157 Each DHCPv6 client and server has a DHCPv6 Unique Identifier (DUID) 158 [RFC3315]. The DUID is designed to be unique across all DHCPv6 159 clients and servers, and to remain stable after it has been initially 160 generated. The DUID can be of different forms. Commonly used forms 161 are based on the link-layer address of one of the device's network 162 interfaces (with or without a timestamp), on the Universally Unique 163 IDentifier (UUID) [RFC6355]. The default type, defined in 164 Section 9.2 of [RFC3315] is DUID-LLT that is based on link-layer 165 address. It is commonly implemented in most popular clients. 167 It is important to understand DUID lifecycle. Clients and servers 168 are expected to generate their DUID once (during first operation) and 169 store it in a non-volatile storage or use the same deterministic 170 algorithm to generate the same DUID value again. This means that 171 most implementations will use the available link-layer address during 172 its first boot. Even if the administrator enables link-layer address 173 randomization, it is likely that it was disabled during the first 174 device boot. Hence the original, unobfuscated link-layer address 175 will likely end up being announced as client DUID, even if the link- 176 layer address has changed (or even if being changed on a periodic 177 basis). The exposure of the original link-layer address in DUID will 178 also undermine other privacy extensions such as [RFC4941]. 180 3.2. Client Identifier Option 182 The Client Identifier Option (OPTION_CLIENTID) [RFC3315] is used to 183 carry the DUID of a DHCPv6 client between a client and a server. 184 There is an analogous Server Identifier Option but it is not as 185 interesting in the privacy context (unless a host can be convinced to 186 start acting as a server). See Section 3.1 for relevant discussion 187 about DUIDs. 189 3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options 191 The Identity Association for Non-temporary Addresses (IA_NA) option 192 [RFC3315] is used to carry the parameters and any non-temporary 193 addresses associated with the given IA_NA. The Identity Association 194 for Temporary Addresses (IA_TA) option [RFC3315] is analogous to the 195 IA_NA option but for temporary addresses. The IA Address option 196 [RFC3315] is used to specify IPv6 addresses associated with an IA_NA 197 or an IA_TA and is encapsulated within the Options field of such an 198 IA_NA or IA_TA option. The Identity Association for Prefix 199 Delegation (IA_PD) [RFC3633] option is used to carry the prefixes 200 that are assigned to the requesting router. IA Prefix option 201 [RFC3633] is used to specify IPv6 prefixes associated with an IA_PD 202 and is encapsulated within the Options field of such an IA_PD option. 204 To differentiate between instances of the same type of IA containers 205 for a client, each IA_NA, IA_TA and IA_PD options have an IAID field 206 with a unique value for a given IA type. It is up to the client to 207 pick unique IAID values. At least one popular implementation uses 208 last four octets of the link-layer address. In most cases, that 209 means that merely two bytes are missing for a full link-layer address 210 reconstruction. However, the first three octets in a typical link- 211 layer address are vendor identifier. That can be determined with 212 high level of certainty using other means, thus allowing full link- 213 layer address discovery. 215 3.4. Client FQDN Option 217 The Client Fully Qualified Domain Name (FQDN) option [RFC4704] is 218 used by DHCPv6 clients and servers to exchange information about the 219 client's fully qualified domain name and about who has the 220 responsibility for updating the DNS with the associated AAAA and PTR 221 RRs. 223 A client can use this option to convey all or part of its domain name 224 to a DHCPv6 server for the IPv6-address-to-FQDN mapping. In most 225 case a client sends its hostname as a hint for the server. The 226 DHCPv6 server MAY be configured to modify the supplied name or to 227 substitute a different name. The server should send its notion of 228 the complete FQDN for the client in the Domain Name field. 230 3.5. Client Link-layer Address Option 232 The Client link-layer address option [RFC6939] is used by first-hop 233 DHCPv6 relays to provide the client's link-layer address towards the 234 server. 236 DHCPv6 relay agents that receive messages originating from clients 237 may include the link-layer source address of the received DHCPv6 238 message in the Client Link-Layer Address option, in relayed DHCPv6 239 Relay-Forward messages. 241 3.6. Option Request Option 243 DHCPv6 clients include an Option Request option [RFC3315] in DHCPv6 244 messages to inform the server about options the client wants the 245 server to send to the client. 247 The content of an Option Request option are the option codes for an 248 option requested by the client. The client may additionally include 249 instances of those options that are identified in the Option Request 250 option, with data values as hints to the server about parameter 251 values the client would like to have returned. 253 3.7. Vendor Class and Vendor-specific Information Options 255 The Vendor Class option, defined in Section 22.16 of [RFC3315] is 256 used by a DHCPv6 client to identify the vendor that manufactured the 257 hardware on which the client is running. 259 The Vendor-specific Information Option, defined in Section 22.17 of 260 [RFC3315] includes enterprise number, which identifies the client's 261 vendor and often includes a number of additional parameters that are 262 specific to a given vendor. That may include any type of information 263 the vendor deems useful. It should be noted that this information 264 may be present (and different) in both directions: client to server 265 and server to client communications. 267 The information contained in the data area of this option is 268 contained in one or more opaque fields that identify details of the 269 hardware configuration, for example, the version of the operating 270 system the client is running or the amount of memory installed on the 271 client. 273 3.8. Civic Location Option 275 DHCPv6 servers use the Civic Location option [RFC4776] to deliver the 276 location information (the civic and postal addresses) from the DHCPv6 277 server to the DHCPv6 clients. It may refer to three locations: the 278 location of the DHCPv6 server, the location of the network element 279 believed to be closest to the client, or the location of the client, 280 identified by the "what" element within the option. 282 3.9. Coordinate-Based Location Option 284 The GeoLoc options [RFC6225] is used by DHCPv6 server to provide the 285 coordinate- based geographic location information to the DHCPv6 286 clients. It enable a DHCPv6 client to obtain its location. 288 3.10. Client System Architecture Type Option 290 The Client System Architecture Type option [RFC5970] is used by 291 DHCPv6 client to send a list of supported architecture types to the 292 DHCPv6 server. It is used by clients that must be booted using the 293 network rather than from local storage, so the server can decide 294 which boot file should be provided to the client. 296 3.11. Relay Agent Options 298 A DHCPv6 relay agent may include a number of options. Those option 299 contain information that can be used to identify the client. Those 300 options are almost exclusively exchanged between the relay agent and 301 the server, thus never leaving the operators network. In particular, 302 they're almost never present in the last wireless hop in case of WiFi 303 networks. The only exception to that rule is somewhat infrequently 304 used Relay Supplied Options option [RFC6422]. This fact implies that 305 the threat model related relay options is slightly different. 306 Traffic sniffing at the last hop and related class of attacks 307 typically do not apply. On the other hand, all attacks that involve 308 operator's intfrastructure (either willing or coerced cooperation or 309 infrastructure being compromised) usually apply. 311 The following subsections describe various options inserted by the 312 relay agents. 314 3.11.1. Subscriber ID Option 316 A DHCPv6 relay may include a Subscriber ID option [RFC4580] to 317 associate some provider-specific information with clients' DHCPv6 318 messages that is independent of the physical network configuration. 320 In many deployments, the relay agent that inserts this option is 321 configured to use client's link-layer address as Subscriber ID. 323 3.11.2. Interface ID Option 325 A DHCPv6 relay includes the Interface ID [RFC3315] option to identify 326 the interface on which it received the client message that is being 327 relayed. 329 Although in principle Interface ID can be arbitrarily long with 330 completely random values, it is sometimes a text string that includes 331 the relay agent name followed by interface name. This can be used 332 for fingerprinting the relay or determining client's point of 333 attachment. 335 3.11.3. Remote ID Option 337 A DHCPv6 relay includes a Remote ID option [RFC4649] to identify the 338 remote host end of the circuit. 340 The remote-id is vendor specific, for which the vendor is indicated 341 in the enterprise-number field. The remote-id field may encode the 342 information that identified the DHCPv6 clients: 344 o a "caller ID" telephone number for dial-up connection 346 o a "user name" prompted for by a Remote Access Server 348 o a remote caller ATM address o a "modem ID" of a cable data modem 350 o the remote IP address of a point-to-point link 352 o an interface or port identifier 354 3.11.4. Relay-ID Option 356 Relay agent may include Relay-ID [RFC5460], which contains a unique 357 relay agent identifier. While its intended use is to provide 358 additional information for the server, so it would be able to respond 359 to leasequeries later, this information can be also used to identify 360 client's location within the network. 362 4. Existing Mechanisms That Affect Privacy 364 This section describes deployed DHCPv6 mechanisms that can affect 365 privacy. 367 4.1. Temporary addresses 369 [RFC3315] defines a mechanism for a client to request temporary 370 addresses. The idea behind temporary addresses is that a client can 371 request a temporary address for a specific purpose, use it, and then 372 never renew it. i.e. let it expire. 374 There are a number of serious issues, both related to protocol and 375 its implementations, that make temporary addresses nearly useless for 376 their original goal. First, [RFC3315] does not include T1 and T2 377 renewal timers in IA_TA (a container for temporary addresses). 378 However, in section 18.1.3 it explicitly mentions that temporary 379 addresses can be renewed. Client implementations may mistakenly 380 renew temporary addresses if they are not careful (i.e., by including 381 the IA_TA with the same IAID in Renew or Rebind requests, rather than 382 a new IAID - see [RFC3315] Section 22.5), thus forfeiting short 383 liveness. [RFC4704] does not explicitly prohibit servers to update 384 DNS for assigned temporary addresses and there are implementations 385 that can be configured to do that. However, this is not advised as 386 publishing a client's IPv6 address in DNS that is publicly available 387 is a major privacy breach. 389 4.2. DNS Updates 391 The Client FQDN Option[RFC4704] used along with DNS Update [RFC2136] 392 defines a mechanism that allows both clients and server to insert 393 into the DNS domain information about clients. Both forward (AAAA) 394 and reverse (PTR) resource records can be updated. This allows other 395 nodes to conveniently refer to a host, despite the fact that its IPv6 396 address may be changing. 398 This mechanism exposes two important pieces of information: current 399 address (which can be mapped to current location) and client's 400 hostname. The stable hostname can then by used to correlate the 401 client across different network attachments even when its IPv6 402 address keeps changing. 404 4.3. Allocation strategies 406 A DHCPv6 server running in typical, stateful mode is given a task of 407 managing one or more pools of IPv6 resources (currently non-temporary 408 addresses, temporary addresses and/or prefixes, but more resource 409 types may be defined in the future). When a client requests a 410 resource, server must pick a resource out of configured pool. 411 Depending on the server's implementation, various allocation 412 strategies are possible. Choices in this regard may have privacy 413 implications. 415 Iterative allocation - a server may choose to allocate addresses one 416 by one. That strategy has the benefit of being very fast, thus can 417 be favored in deployments that prefer performance. However, it makes 418 the resources very predictable. Also, since the resources allocated 419 tend to be clustered at the beginning of available pool, it makes 420 scanning attacks much easier. 422 Identifier-based allocation - some server implementations use a fixed 423 identifier for a specific client, seemingly taken from the client's 424 MAC address when available or some lower bits of client's source IPv6 425 address. This has a property of being convenient for converting IP 426 address to/from other identifiers, especially if the identifier is or 427 contains MAC address. It is also convenient, as returning client is 428 very likely to get the same address, even if the server does not 429 retain previous client's address. Those properties are convenient 430 for system administrators, so DHCPv6 server implementors are 431 sometimes requested to implement it. There is at least one 432 implementation that supports it. The downside of such allocation is 433 that the client now discloses its identifier in its IPv6 address to 434 all services it connects to. That means that correlation of 435 activities over time, location tracking, address scanning and OS/ 436 vendor discovery apply. 438 Hash allocation - it's an extension of identifier based allocation. 439 Instead of using the identifier directly, it is being hashed first. 440 If the hash is implemented correctly, it removes the flaw of 441 disclosing the identifier, a property that eliminates susceptibility 442 to address scanning and OS/vendor discovery. If the hash is poorly 443 implemented (e.g. can be reverted), it introduces no improvement over 444 identifier-based allocation. 446 Random allocation - a server can pick a resource randomly out of 447 available pool. That strategy works well in scenarios where pool 448 utilization is small, as the likelihood of collision (resulting in 449 the server needing to repeat randomization) is small. With the pool 450 allocation increasing, the collision is disproportionally large, due 451 to birthday paradox. With high pool utilization (e.g. when 90% of 452 available resources being allocated already), the server will use 453 most computational resources to repeatedly pick a random resource, 454 which will degrade its performance. This allocation scheme 455 essentially prevents returning clients from getting the same address 456 or prefix again. On the other hand, it is beneficial from privacy 457 perspective as addresses and prefixes generated that way are not 458 susceptible to correlation attacks, OS/vendor discovery attacks or 459 identity discovery attacks. Note that even though the address or 460 prefix itself may be resilient to a given attack, the client may 461 still be susceptible if additional information is disclosed other 462 way, e.g. client's address can be randomized, but it still can leak 463 its MAC address in client-id option. 465 Other allocation strategies may be implemented. 467 5. Attacks 469 5.1. Device type discovery (fingerprinting) 471 The type of device used by the client can be guessed by the attacker 472 using the Vendor Class option, Vendor-specific Information option, 473 the Client Link-layer Address option, and by parsing the Client ID 474 option. All of those options may contain OUI (Organizationally 475 Unique Identifier) that represents the device's vendor. That 476 knowledge can be used for device-specific vulnerability exploitation 477 attacks. See Section 3.4 of 479 [I-D.ietf-6man-ipv6-address-generation-privacy] for a discussion 480 about this type of attack. 482 5.2. Operating system discovery (fingerprinting) 484 The operating system running on a client can be guessed using the 485 Vendor Class option, the Vendor-specific Information option, the 486 Client System Architecture Type option, or by using fingerprinting 487 techniques on the combination of options requested using the Option 488 Request option. See Section 3.4 of 489 [I-D.ietf-6man-ipv6-address-generation-privacy] for a discussion 490 about this type of attack. 492 5.3. Finding location information 494 The location information can be obtained by the attacker by many 495 means. The most direct way to obtain this information is by looking 496 into a message originating from the server that contains the Civic 497 Location or GeoLoc option. It can also be indirectly inferred using 498 the Remote ID Option, the Interface ID option (e.g. if an access 499 circuit on an Access Node corresponds to a civic location), or the 500 Subscriber ID Option (if the attacker has access to subscriber 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 masquerade as an access concentrator, either DHCPv6 573 relay agent or DHCPv6 client, to obtain location information directly 574 from the DHCP server(s) using the DHCPv6 Leasequery [RFC5007] 575 mechanism. 577 Location information is information needed by the access concentrator 578 to forward traffic to a broadband-accessible host. This information 579 includes knowledge of the host hardware address, the port or virtual 580 circuit that leads to the host, and/or the hardware address of the 581 intervening subscriber modem. 583 Furthermore, the attackers may use DHCPv6 bulk leasequery [RFC5460] 584 mechanism to obtain bulk information about DHCPv6 bindings, even 585 without knowing the target bindings. 587 Additionally, active leasequery [RFC7653] is a mechanism for 588 subscribing to DHCPv6 lease update changes in near real-time. The 589 intent of this mechanism is to update operator's database, but if 590 misused, an attacker could defeat server's authentication mechanisms 591 and subscribe to all updates. He then could continue receiving 592 updates, without any need for local presence. 594 6. Security Considerations 596 In current practice, the client privacy and the client authentication 597 are mutually exclusive. The client authentication procedure reveals 598 additional client information in their certificates/identifiers. 599 Full privacy for the clients may mean the clients are also anonymous 600 for the server and the network. 602 7. Privacy Considerations 604 This document at its entirety discusses privacy considerations in 605 DHCPv6. As such, no dedicated discussion is needed. 607 8. IANA Considerations 609 This draft does not request any IANA action. 611 9. Acknowledgements 613 The authors would like to thank Stephen Farrell, Ted Lemon, Ines 614 Robles, Russ White, Christian Schaefer, Jinmei Tatuya, Bernie Volz, 615 Marcin Siodelski, Christian Huitema, Brian Haberman and other members 616 of DHC WG for their valuable comments. 618 This document was produced using the xml2rfc tool [RFC2629]. 620 10. References 622 10.1. Normative References 624 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 625 Requirement Levels", BCP 14, RFC 2119, 626 DOI 10.17487/RFC2119, March 1997, 627 . 629 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 630 C., and M. Carney, "Dynamic Host Configuration Protocol 631 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 632 2003, . 634 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 635 Morris, J., Hansen, M., and R. Smith, "Privacy 636 Considerations for Internet Protocols", RFC 6973, 637 DOI 10.17487/RFC6973, July 2013, 638 . 640 [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an 641 Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 642 2014, . 644 10.2. Informative References 646 [I-D.ietf-6man-ipv6-address-generation-privacy] 647 Cooper, A., Gont, F., and D. Thaler, "Privacy 648 Considerations for IPv6 Address Generation Mechanisms", 649 draft-ietf-6man-ipv6-address-generation-privacy-08 (work 650 in progress), September 2015. 652 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 653 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 654 RFC 2136, DOI 10.17487/RFC2136, April 1997, 655 . 657 [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, 658 DOI 10.17487/RFC2629, June 1999, 659 . 661 [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic 662 Host Configuration Protocol (DHCP) version 6", RFC 3633, 663 DOI 10.17487/RFC3633, December 2003, 664 . 666 [RFC4580] Volz, B., "Dynamic Host Configuration Protocol for IPv6 667 (DHCPv6) Relay Agent Subscriber-ID Option", RFC 4580, 668 DOI 10.17487/RFC4580, June 2006, 669 . 671 [RFC4649] Volz, B., "Dynamic Host Configuration Protocol for IPv6 672 (DHCPv6) Relay Agent Remote-ID Option", RFC 4649, 673 DOI 10.17487/RFC4649, August 2006, 674 . 676 [RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for 677 IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN) 678 Option", RFC 4704, DOI 10.17487/RFC4704, October 2006, 679 . 681 [RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol 682 (DHCPv4 and DHCPv6) Option for Civic Addresses 683 Configuration Information", RFC 4776, 684 DOI 10.17487/RFC4776, November 2006, 685 . 687 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 688 Extensions for Stateless Address Autoconfiguration in 689 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 690 . 692 [RFC5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng, 693 "DHCPv6 Leasequery", RFC 5007, DOI 10.17487/RFC5007, 694 September 2007, . 696 [RFC5460] Stapp, M., "DHCPv6 Bulk Leasequery", RFC 5460, 697 DOI 10.17487/RFC5460, February 2009, 698 . 700 [RFC5970] Huth, T., Freimann, J., Zimmer, V., and D. Thaler, "DHCPv6 701 Options for Network Boot", RFC 5970, DOI 10.17487/RFC5970, 702 September 2010, . 704 [RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, Ed., 705 "Dynamic Host Configuration Protocol Options for 706 Coordinate-Based Location Configuration Information", 707 RFC 6225, DOI 10.17487/RFC6225, July 2011, 708 . 710 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 711 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 712 DOI 10.17487/RFC6355, August 2011, 713 . 715 [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", 716 RFC 6422, DOI 10.17487/RFC6422, December 2011, 717 . 719 [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer 720 Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939, 721 May 2013, . 723 [RFC7653] Raghuvanshi, D., Kinnear, K., and D. Kukrety, "DHCPv6 724 Active Leasequery", RFC 7653, DOI 10.17487/RFC7653, 725 October 2015, . 727 Authors' Addresses 729 Suresh Krishnan 730 Ericsson 731 8400 Decarie Blvd. 732 Town of Mount Royal, QC 733 Canada 735 Phone: +1 514 345 7900 x42871 736 Email: suresh.krishnan@ericsson.com 738 Tomek Mrugalski 739 Internet Systems Consortium, Inc. 740 950 Charter Street 741 Redwood City, CA 94063 742 USA 744 Email: tomasz.mrugalski@gmail.com 746 Sheng Jiang 747 Huawei Technologies Co., Ltd 748 Q14, Huawei Campus, No.156 BeiQing Road 749 Hai-Dian District, Beijing 100095 750 P.R. China 752 Email: jiangsheng@huawei.com