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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) ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 4941 (Obsoleted by RFC 8981) -- Obsolete informational reference (is this intentional?): RFC 1948 (Obsoleted by RFC 6528) == Outdated reference: A later version (-08) exists of draft-ietf-opsec-ipv6-host-scanning-00 Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 maintenance Working Group (6man) F. Gont 3 Internet-Draft SI6 Networks / UTN-FRH 4 Intended status: Standards Track January 27, 2013 5 Expires: July 31, 2013 7 A method for Generating Stable Privacy-Enhanced Addresses with IPv6 8 Stateless Address Autoconfiguration (SLAAC) 9 draft-ietf-6man-stable-privacy-addresses-03 11 Abstract 13 This document specifies a method for generating IPv6 Interface 14 Identifiers to be used with IPv6 Stateless Address Autoconfiguration 15 (SLAAC), such that addresses configured using this method are stable 16 within each subnet, but the Interface Identifier changes when hosts 17 move from one network to another. The aforementioned method is meant 18 to be an alternative to generating Interface Identifiers based on 19 IEEE identifiers, such that the benefits of stable addresses can be 20 achieved without sacrificing the privacy of users. 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 July 31, 2013. 39 Copyright Notice 41 Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Design goals . . . . . . . . . . . . . . . . . . . . . . . . . 6 58 3. Algorithm specification . . . . . . . . . . . . . . . . . . . 7 59 4. Resolving Duplicate Address Detection (DAD) conflicts . . . . 10 60 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 61 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 62 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 63 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 64 8.1. Normative References . . . . . . . . . . . . . . . . . . . 14 65 8.2. Informative References . . . . . . . . . . . . . . . . . . 14 66 Appendix A. Privacy issues still present with RFC 4941 . . . . . 16 67 A.1. Host tracking . . . . . . . . . . . . . . . . . . . . . . 16 68 A.1.1. Tracking hosts across networks #1 . . . . . . . . . . 16 69 A.1.2. Tracking hosts across networks #2 . . . . . . . . . . 16 70 A.1.3. Revealing the identity of devices performing 71 server-like functions . . . . . . . . . . . . . . . . 17 72 A.2. Address scanning attacks . . . . . . . . . . . . . . . . . 17 73 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18 75 1. Introduction 77 [RFC4862] specifies the Stateless Address Autoconfiguration (SLAAC) 78 for IPv6 [RFC2460], which typically results in hosts configuring one 79 or more "stable" addresses composed of a network prefix advertised by 80 a local router, and an Interface Identifier (IID) that typically 81 embeds a hardware address (e.g., using IEEE identifiers) [RFC4291]. 83 Generally, stable addresses are thought to simplify network 84 management, since they simplify Access Control Lists (ACLs) and 85 logging. However, since IEEE identifiers are typically globally 86 unique, the resulting IPv6 addresses can be leveraged to track and 87 correlate the activity of a node over time and across multiple 88 subnets and networks, thus negatively affecting the privacy of users. 90 The "Privacy Extensions for Stateless Address Autoconfiguration in 91 IPv6" [RFC4941] were introduced to complicate the task of 92 eavesdroppers and other information collectors to correlate the 93 activities of a node, and basically result in temporary (and random) 94 Interface Identifiers that are typically more difficult to leverage 95 than those based on IEEE identifiers. When privacy extensions are 96 enabled, "privacy addresses" are employed for "outgoing 97 communications", while the traditional IPv6 addresses based on IEEE 98 identifiers are still used for "server" functions (i.e., receiving 99 incoming connections). 101 As noted in [RFC4941], "anytime a fixed identifier is used in 102 multiple contexts, it becomes possible to correlate seemingly 103 unrelated activity using this identifier". Therefore, since 104 "privacy addresses" [RFC4941] do not eliminate the use of fixed 105 identifiers for server-like functions, they only *partially* 106 mitigate the correlation of host activities (see Appendix A for 107 some example attacks that are still possible with privacy 108 addresses). Therefore, it is vital that the privacy 109 characteristics of "stable" addresses are improved such that the 110 ability of an attacker correlating host activities across networks 111 is reduced. 113 Another important aspect not mitigated by "Privacy Addresses" 114 [RFC4941] is that of host scanning. Since IPv6 addresses that 115 embed IEEE identifiers have specific patterns, an attacker could 116 leverage such patterns to greatly reduce the search space for 117 "live" hosts. Since "privacy addresses" do not eliminate the use 118 of IPv6 addresses that embed IEEE identifiers, host scanning 119 attacks are still feasible even if "privacy extensions" are 120 employed [Gont-DEEPSEC2011] [CPNI-IPv6]. This is yet another 121 motivation to improve the privacy characteristics of "stable" 122 addresses (currently embedding IEEE identifiers). 124 Privacy/temporary addresses can be challenging in a number of areas. 125 For example, from a network-management point of view, they tend to 126 increase the complexity of event logging, trouble-shooting, and 127 enforcing access controls and quality of service, etc. As a result, 128 some organizations disable the use of privacy addresses even at the 129 expense of reduced privacy [Broersma]. Also, they result in 130 increased complexity, which might not be possible or desirable in 131 some implementations (e.g., some embedded devices). 133 In scenarios in which "Privacy Extensions" are deliberately not used 134 (possibly for any of the aforementioned reasons), all a host is left 135 with is the addresses that have been generated using e.g. IEEE 136 identifiers, and this is yet another case in which it is also vital 137 that the privacy characteristics of these stable addresses are 138 improved. 140 We note that in most (if not all) of those scenarios in which 141 "Privacy Extensions" are disabled, there is usually no actual desire 142 to negatively affect user privacy, but rather a desire to simplify 143 operation of the network (simplify the use of ACLs, logging, etc.). 145 This document specifies a method to generate interface identifiers 146 that are stable/constant within each subnet, but that change as hosts 147 move from one network to another, thus keeping the "stability" 148 properties of the interface identifiers specified in [RFC4291], while 149 still mitigating host-scanning attacks and preventing correlation of 150 the activities of a node as it moves from one network to another. 152 This document does not update or modify IPv6 StateLess Address Auto- 153 Configuration (SLAAC) [RFC4862] itself, but rather only specifies an 154 alternative algorithm to generate Interface IDs. Therefore, the 155 usual address lifetime properties (as specified in the corresponding 156 Prefix Information Options) apply when IPv6 addresses are generated 157 as a result of employing the algorithm specified in this document 158 with SLAAC [RFC4862]. Additionally, from the point of view of 159 renumbering, we note that these addresses behave like the traditional 160 IPv6 addresses (that embed a hardware address) resulting from SLAAC 161 [RFC4862]. 163 For nodes that currently disable "Privacy extensions" [RFC4941] for 164 some of the reasons stated above, this mechanism provides stable 165 privacy-enhanced addresses which may already address most of the 166 privacy concerns related to addresses that embed IEEE identifiers 167 [RFC4291]. On the other hand, in scenarios in which "Privacy 168 Extensions" are employed, implementation of the mechanism described 169 in this document would mitigate host-scanning attacks and also 170 mitigate correlation of host activities. 172 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 173 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 174 document are to be interpreted as described in RFC 2119 [RFC2119]. 176 2. Design goals 178 This document specifies a method for selecting interface identifiers 179 to be used with IPv6 SLAAC, with the following goals: 181 o The resulting interface identifiers remain constant/stable for 182 each prefix used with SLAAC within each subnet. That is, the 183 algorithm generates the same interface identifier when configuring 184 an address belonging to the same prefix within the same subnet. 186 o The resulting interface identifiers do not depend on the 187 underlying hardware (e.g. link-layer address). This means that 188 e.g. replacing a Network Interface Card (NIC) will not have the 189 (generally undesirable) effect of changing the IPv6 addresses used 190 for that network interface. 192 o The resulting interface identifiers do change when addresses are 193 configured for different prefixes. That is, if different 194 autoconfiguration prefixes are used to configure addresses for the 195 same network interface card, the resulting interface identifiers 196 must be (statistically) different. 198 o It must be difficult for an outsider to predict the interface 199 identifiers that will be generated by the algorithm, even with 200 knowledge of the interface identifiers generated for configuring 201 other addresses. 203 o The aforementioned interface identifiers are meant to be an 204 alternative to those based on e.g. IEEE identifiers, such as 205 those specified in [RFC2464]. 207 We note that of use of the algorithm specified in this document is 208 (to a large extent) orthogonal to the use of "Privacy Extensions" 209 [RFC4941]. Hosts that do not implement/use "Privacy Extensions" 210 would have the benefit that they would not be subject to the host- 211 tracking and host scanning issues discussed in the previous section. 212 On the other hand, in the case of hosts employing "Privacy 213 Extensions", the method specified in this document would prevent host 214 scanning attacks and correlation of node activities across networks 215 (see Appendix A). 217 3. Algorithm specification 219 IPv6 implementations conforming to this specification MUST generate 220 interface identifiers using the algorithm specified in this section 221 in replacement of any other algorithms used for generating "stable" 222 addresses (such as that specified in [RFC2464]). The aforementioned 223 algorithm MUST be employed for generating the interface identifiers 224 for all of the IPv6 addresses configured with SLAAC for a given 225 interface, including IPv6 link-local addresses. 227 This means that this document does not formally obsolete or 228 deprecate any of the existing algorithms to generate Interface IDs 229 (e.g. such as that specified in [RFC2464]). However, those IPv6 230 implementations that employ this specification must generate all 231 of their "stable" addresses as specified in this document. 233 Implementations conforming to this specification SHOULD provide the 234 means for a system administrator to enable or disable the use of this 235 algorithm for generating Interface Identifiers. Implementations 236 conforming to this specification MAY employ the algorithm specified 237 in [RFC4941] to generate temporary addresses in addition to the 238 addresses generated with the algorithm specified in this document. 240 Unless otherwise noted, all of the parameters included in the 241 expression below MUST be included when generating an Interface ID. 243 1. Compute a random (but stable) identifier with the expression: 245 RID = F(Prefix, Interface_Index, Network_ID, DAD_Counter, 246 secret_key) 248 Where: 250 RID: 251 Random (but stable) identifier 253 F(): 254 A pseudorandom function (PRF) that is not computable from the 255 outside (without knowledge of the secret key). The PRF could 256 be implemented as a cryptographic hash of the concatenation of 257 each of the function parameters. 259 Prefix: 260 The prefix to be used for SLAAC, as learned from an ICMPv6 261 Router Advertisement message. 263 Interface_Index: 264 The interface index [RFC3493] [RFC3542] corresponding to this 265 network interface. 267 Network_ID: 268 Some network specific data that identifies the subnet to which 269 this interface is attached. For example the IEEE 802.11 270 Service Set Identifier (SSID) corresponding to the network to 271 which this interface is associated. This parameter is 272 OPTIONAL. 274 DAD_Counter: 275 A counter that is employed to resolve Duplicate Address 276 Detection (DAD) conflicts. It MUST be initialized to 0, and 277 incremented by 1 for each new tentative address that is 278 configured as a result of a DAD conflict. Implementations 279 that record DAD_Counter in non-volatile memory for each 280 {Prefix, Interface_Index, Network_ID} tuple MUST initialize 281 DAD_Counter to the recorded value if such an entry exists in 282 non-volatile memory). See Section 4 for additional details. 284 secret_key: 285 A secret key that is not known by the attacker. The secret 286 key MUST be initialized at system installation time to a 287 pseudo-random number (see [RFC4086] for randomness 288 requirements for security). An implementation MAY provide the 289 means for the user to change the secret key. 291 2. The Interface Identifier is finally obtained by taking the 292 leftmost 64 bits of the RID value computed in the previous step, 293 and setting bit 6 (the leftmost bit is numbered 0) to zero. This 294 creates an interface identifier with the universal/local bit 295 indicating local significance only. The resulting Interface 296 Identifier should be compared against the list of reserved 297 interface identifiers [IANA-RESERVED-IID], and to those interface 298 identifiers already employed in an address of the same network 299 interface and the same network prefix. In the event that an 300 unacceptable identifier has been generated, this situation should 301 be handled in the same way as the case of duplicate addresses 302 (see Section 4). 304 This document does not require the use of any specific PRF for the 305 function F() above, since the choice of such PRF is usually a trade- 306 off between a number of properties (processing requirements, ease of 307 implementation, possible intellectual property rights, etc.), and 308 since the best possible choice for F() might be different for 309 different types of devices (e.g. embedded systems vs. regular 310 servers) and might possibly change over time. 312 Note that the result of F() in the algorithm above is no more secure 313 than the secret key. If an attacker is aware of the PRF that is 314 being used by the victim (which we should expect), and the attacker 315 can obtain enough material (i.e. addresses configured by the victim), 316 the attacker may simply search the entire secret-key space to find 317 matches. To protect against this, the secret key should be of a 318 reasonable length. Key lengths of at least 128 bits should be 319 adequate. The secret key is initialized at system installation time 320 to a pseudo-random number, thus allowing this mechanism to be 321 enabled/used automatically, without user intervention. 323 Including the SLAAC prefix in the PRF computation causes the 324 Interface ID to vary across networks that employ different prefixes, 325 thus mitigating host-tracking attacks and any other attacks that 326 benefit from predictable Interface IDs (such as host scanning). 328 Including the optional Network_ID parameter when computing the RID 329 value above would cause the algorithm to produce a different 330 Interface Identifier when connecting to different networks, even when 331 configuring addresses belonging to the same prefix. This means that 332 a host would employ a different Interface ID as it moves from one 333 network to another even for IPv6 link-local addresses or Unique Local 334 Addresses (ULAs). 336 4. Resolving Duplicate Address Detection (DAD) conflicts 338 If as a result of performing Duplicate Address Detection (DAD) 339 [RFC4862] a host finds that the tentative address generated with the 340 algorithm specified in Section 3 is a duplicate address, it SHOULD 341 resolve the address conflict by trying a new tentative address as 342 follows: 344 o DAD_Counter is incremented by 1. 346 o A new Interface ID is generated with the algorithm specified in 347 Section 3, using the incremented DAD_Counter value. 349 This procedure may be repeated a number of times until the address 350 conflict is resolved. We RECOMMEND hosts to try at least 351 IDGEN_RETRIES (hereby specified as "3") tentative addresses if DAD 352 fails for successive generated addresses, in the hopes of resolving 353 the address conflict. We also note that hosts MUST limit the number 354 of tentative addresses that are tried (rather than indefinitely try a 355 new tentative address until the conflict is resolved). 357 In those (unlikely) scenarios in which duplicate addresses are 358 detected and in which the order in which the conflicting nodes 359 configure their addresses may vary (e.g., because they may be 360 bootstrapped in different order), the algorithm specified in this 361 section for resolving DAD conflicts could lead to addresses that are 362 not stable within the same subnet. In order to mitigate this 363 potential problem, nodes MAY record the DAD_Counter value employed 364 for a specific {Prefix, Interface_Index, Network_ID} tuple in non- 365 volatile memory, such that the same DAD_Counter value is employed 366 when configuring an address for the same Prefix and subnet at any 367 other point in time. 369 In the event that a DAD conflict cannot be solved (possibly after 370 trying a number of different addresses), address configuration would 371 fail. In those scenarios, nodes MUST NOT automatically fall back to 372 employing other algorithms for generating interface identifiers. 374 5. IANA Considerations 376 There are no IANA registries within this document. The RFC-Editor 377 can remove this section before publication of this document as an 378 RFC. 380 6. Security Considerations 382 This document specifies an algorithm for generating interface 383 identifiers to be used with IPv6 Stateless Address Autoconfiguration 384 (SLAAC), as an alternative to e.g. interface identifiers that embed 385 IEEE identifiers (such as those specified in [RFC2464]). When 386 compared to such identifiers, the identifiers specified in this 387 document have a number of advantages: 389 o They prevent trivial host-tracking, since when a host moves from 390 one network to another the network prefix used for 391 autoconfiguration and/or the Network ID (e.g., IEEE 802.11 SSID) 392 will typically change, and hence the resulting interface 393 identifier will also change (see Appendix A. 395 o They mitigate address-scanning techniques which leverage 396 predictable interface identifiers (e.g., known Organizational 397 Unique Identifiers) [I-D.ietf-opsec-ipv6-host-scanning]. 399 o They result in IPv6 addresses that are independent of the 400 underlying hardware (i.e. the resulting IPv6 addresses do not 401 change if a network interface card is replaced). 403 We note that this algorithm is meant to be an alternative to 404 interface identifiers such as those specified in [RFC2464], but is 405 not meant as an alternative to temporary Interface IDs (such as those 406 specified in [RFC4941]). Clearly, temporary addresses may help to 407 mitigate the correlation of activities of a node within the same 408 network, and may also reduce the attack exposure window (since 409 privacy/temporary addresses are short-lived when compared to the 410 addresses generated with the method specified in this document). We 411 note that implementation of this algorithm would still benefit those 412 hosts employing "Privacy Addresses", since it would mitigate host- 413 tracking vectors still present when privacy addresses are used (see 414 Appendix A), and would also mitigate host-scanning techniques that 415 leverage patterns in IPv6 addresses that embed IEEE identifiers. 417 Finally, we note that the method described in this document may 418 mitigate most of the privacy concerns arising from the use of IPv6 419 addresses that embed IEEE identifiers, without the use of temporary 420 addresses, thus possibly offering an interesting trade-off for those 421 scenarios in which the use of temporary addresses is not feasible. 423 7. Acknowledgements 425 The algorithm specified in this document has been inspired by Steven 426 Bellovin's work ([RFC1948]) in the area of TCP sequence numbers. 428 The author would like to thank (in alphabetical order) Karl Auer, 429 Steven Bellovin, Matthias Bethke, Brian Carpenter, Tassos 430 Chatzithomaoglou, Dominik Elsbroek, Bob Hinden, Christian Huitema, 431 Ray Hunter, Jong-Hyouk Lee, Michael Richardson, and Ole Troan, for 432 providing valuable comments on earlier versions of this document. 434 This document is based on the technical report "Security Assessment 435 of the Internet Protocol version 6 (IPv6)" [CPNI-IPv6] authored by 436 Fernando Gont on behalf of the UK Centre for the Protection of 437 National Infrastructure (CPNI). 439 Fernando Gont would like to thank CPNI (http://www.cpni.gov.uk) for 440 their continued support. 442 8. References 444 8.1. Normative References 446 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 447 (IPv6) Specification", RFC 2460, December 1998. 449 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 450 Requirement Levels", BCP 14, RFC 2119, March 1997. 452 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 453 Requirements for Security", BCP 106, RFC 4086, June 2005. 455 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 456 Architecture", RFC 4291, February 2006. 458 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 459 Address Autoconfiguration", RFC 4862, September 2007. 461 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 462 Extensions for Stateless Address Autoconfiguration in 463 IPv6", RFC 4941, September 2007. 465 8.2. Informative References 467 [RFC1948] Bellovin, S., "Defending Against Sequence Number Attacks", 468 RFC 1948, May 1996. 470 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 471 Networks", RFC 2464, December 1998. 473 [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. 474 Stevens, "Basic Socket Interface Extensions for IPv6", 475 RFC 3493, February 2003. 477 [RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei, 478 "Advanced Sockets Application Program Interface (API) for 479 IPv6", RFC 3542, May 2003. 481 [I-D.ietf-opsec-ipv6-host-scanning] 482 Gont, F. and T. Chown, "Network Reconnaissance in IPv6 483 Networks", draft-ietf-opsec-ipv6-host-scanning-00 (work in 484 progress), December 2012. 486 [IANA-RESERVED-IID] 487 Reserved IPv6 Interface Identifiers, "http://www.iana.org/ 488 assignments/ipv6-interface-ids/ipv6-interface-ids.xml". 490 [Gont-DEEPSEC2011] 491 Gont, "Results of a Security Assessment of the Internet 492 Protocol version 6 (IPv6)", DEEPSEC 2011 Conference, 493 Vienna, Austria, November 2011, . 497 [Gont-BRUCON2012] 498 Gont, "Recent Advances in IPv6 Security", BRUCON 2012 499 Conference, Ghent, Belgium, September 2012, . 503 [Broersma] 504 Broersma, R., "IPv6 Everywhere: Living with a Fully IPv6- 505 enabled environment", Australian IPv6 Summit 2010, 506 Melbourne, VIC Australia, October 2010, 507 . 509 [CPNI-IPv6] 510 Gont, F., "Security Assessment of the Internet Protocol 511 version 6 (IPv6)", UK Centre for the Protection of 512 National Infrastructure, (available on request). 514 Appendix A. Privacy issues still present with RFC 4941 516 This section aims to clarify the motivation of using the method 517 specified in this document even when privacy/temporary addresses 518 [RFC4941] are employed. It discusses a (non-exaustive) number of 519 scenarios in which host privacy is still sacrificed even when 520 privacy/temporary addresses [RFC4941] are employed, as a result of 521 employing interface identifiers that are constant across networks 522 (e.g., those resulting from embedding IEEE identifiers). 524 A.1. Host tracking 526 This section describes one possible attack scenario that illustrates 527 that host-tracking may still be possible when privacy/temporary 528 addresses [RFC4941] are employed. 530 A.1.1. Tracking hosts across networks #1 532 A host configures its stable addresses with the constant 533 Interface-ID, and runs any application that needs to perform a 534 server-like function (e.g. a peer-to-peer application). As a result 535 of that, an attacker/user participating in the same application 536 (e.g., P2P) would learn the constant Interface-ID used by the host 537 for that network interface. 539 Some time later, the same host moves to a completely different 540 network, and employs the same P2P application, probably even with a 541 different username. The attacker now interacts with the same host 542 again, and hence can learn its newly-configured stable address. 543 Since the interface ID is the same as the one used before, the 544 attacker can infer that it is communicating with the same device as 545 before. 547 This is just *one* possible attack scenario, which should remind us 548 that one should not disclose more than it is really needed for 549 achieving a specific goal (and an Interface-ID that is constant 550 across different networks does exactly that: it discloses more 551 information than is needed for providing a stable address). 553 A.1.2. Tracking hosts across networks #2 555 Once an attacker learns the constant Interface-ID employed by the 556 victim host for its stable address, the attacker is able to "probe" a 557 network for the presence of such host at any given network. 559 See Appendix A.1.1 for just one example of how an attacker could 560 learn such value. Other examples include being able to share the 561 same network segment at some point in time (e.g. a conference 562 network or any public network), etc. 564 For example, if an attacker learns that in one network the victim 565 used the Interface-ID 1111:2222:3333:4444 for its stable addresses, 566 then he could subsequently probe for the presence of such device in 567 the network 2011:db8::/64 by sending a probe packet (ICMPv6 Echo 568 Request, or any other probe packet) to the address 2001:db8::1111: 569 2222:3333:4444. 571 A.1.3. Revealing the identity of devices performing server-like 572 functions 574 Some devices, such as storage devices or printers, may typically 575 perform server-like functions and may be usually moved from one 576 network to another. Such devices are likely to simply disable (or 577 not even implement) privacy/temporary addresses [RFC4941]. If the 578 aforementioned devices employ Interface-IDs that are constant across 579 networks, it would be trivial for an attacker to tell whether the 580 same device is being used across networks by simply looking at the 581 Interface ID. Clearly, performing server-like functions should not 582 imply that a device discloses its identity (i.e., that the attacker 583 can tell whether it is the same device providing some function in two 584 different networks, at two different points in time). 586 The scheme proposed in this document prevents such information 587 leakage by causing nodes to generate different Interface-IDs when 588 moving to one network to another, thus mitigating this kind of 589 privacy attack. 591 A.2. Address scanning attacks 593 While it is usually assumed that address-scanning attacks are 594 unfeasible, an attacker could leverage patterns in IPv6 addresses to 595 greatly reduce the search space [I-D.ietf-opsec-ipv6-host-scanning] 596 [Gont-BRUCON2012]. 598 As noted earlier in this document, privacy/temporary addresses do not 599 eliminate the use of IPv6 addresses that embed IEEE identifiers, and 600 hence such hosts would still be vulnerable to address-scanning 601 attacks. The method specified in this document eliminates such 602 patterns and would thus mitigate the aforementioned address-scanning 603 attacks. 605 Author's Address 607 Fernando Gont 608 SI6 Networks / UTN-FRH 609 Evaristo Carriego 2644 610 Haedo, Provincia de Buenos Aires 1706 611 Argentina 613 Phone: +54 11 4650 8472 614 Email: fgont@si6networks.com 615 URI: http://www.si6networks.com