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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-05) exists of draft-ietf-dnssd-privacy-00 -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 4941 (Obsoleted by RFC 8981) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force R. Winter 3 Internet-Draft University of Applied Sciences Augsburg 4 Intended status: Informational M. Faath 5 Expires: July 23, 2018 Conntac GmbH 6 F. Weisshaar 7 University of Applied Sciences Augsburg 8 January 19, 2018 10 Privacy considerations for protocols relying on IP broadcast and 11 multicast 12 draft-ietf-intarea-broadcast-consider-08 14 Abstract 16 A number of application-layer protocols make use of IP broadcasts or 17 multicast messages for functions like local service discovery or name 18 resolution. Some of these functions can only be implemented 19 efficiently using such mechanisms. When using broadcasts or 20 multicast messages, a passive observer in the same broadcast/ 21 multicast domain can trivially record these messages and analyze 22 their content. Therefore, designers of protocols that make use 23 broadcast/multicast messages need to take special care when designing 24 their protocols. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on July 23, 2018. 43 Copyright Notice 45 Copyright (c) 2018 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 1.1. Types and usage of broadcast and multicast . . . . . . . 4 62 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 63 2. Privacy considerations . . . . . . . . . . . . . . . . . . . 5 64 2.1. Message frequency . . . . . . . . . . . . . . . . . . . . 5 65 2.2. Persistent identifiers . . . . . . . . . . . . . . . . . 5 66 2.3. Anticipate user behavior . . . . . . . . . . . . . . . . 6 67 2.4. Consider potential correlation . . . . . . . . . . . . . 7 68 2.5. Configurability . . . . . . . . . . . . . . . . . . . . . 7 69 3. Operational considerations . . . . . . . . . . . . . . . . . 8 70 4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 71 5. Other considerations . . . . . . . . . . . . . . . . . . . . 9 72 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 73 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 74 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 75 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 76 9.1. Normative References . . . . . . . . . . . . . . . . . . 10 77 9.2. Informative References . . . . . . . . . . . . . . . . . 10 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 80 1. Introduction 82 Broadcast and multicast messages have a large (and to the sender 83 unknown) receiver group by design. Because of that, these two 84 mechanisms are vital for a number of basic network functions such as 85 auto-configuration or link-layer address lookup. Also application 86 developers use broadcast/multicast messages to implement things like 87 local service or peer discovery. It appears that an increasing 88 number of applications make use of it as suggested by experimental 89 results obtained on campus networks including the IETF meeting 90 network [TRAC2016]. This trend is not entirely surprising. As RFC 91 919 [RFC0919] puts it, "The use of broadcasts [...] is a good base 92 for many applications". Broadcast and multicast functionality in a 93 subnetwork are therefore important as a lack thereof renders the 94 protocols relying on these mechanisms inoperable [RFC3819]. 96 Using broadcast/multicast can become problematic if the information 97 that is being distributed can be regarded as sensitive or when the 98 information that is distributed by multiple of these protocols can be 99 correlated in a way that sensitive data can be derived. This is 100 clearly true for any protocol, but broadcast/multicast is special in 101 at least two respects: 103 (a) The aforementioned large receiver group, consisting of receivers 104 unknown to the sender. This makes eavesdropping without special 105 privileges or a special location in the network trivial for 106 anybody in the same broadcast/multicast domain. 108 (b) Encryption is difficult when broadcast/multicast messages are 109 used, for instance because a non-trivial key management protocol 110 might be required. When encryption is not used, the content of 111 these messages is easily accessible, making it easy to spoof and 112 replay them. 114 Given the above, privacy protection for protocols based on broadcast 115 or multicast communication is significantly more difficult compared 116 to unicast communication and at the same time invading the privacy is 117 much easier. 119 Privacy considerations of IETF-specified protocols have received some 120 attention in the recent past (e.g. RFC 7721 [RFC7721] or RFC 7819 121 [RFC7819]). There is also general guidance available for document 122 authors on when and how to include a privacy considerations section 123 in their documents and on how to evaluate the privacy implications of 124 Internet protocols [RFC6973]. RFC6973 also describes potential 125 threats to privacy in great detail and lists terminology that is also 126 used in this document. In contrast to RFC6973, this document 127 contains a number of privacy considerations especially for protocols 128 that rely on broadcast/multicast, intended to reduce the likelihood 129 that a broadcast/multicast protocol can be misused to collect 130 sensitive data about devices, users and groups of users on a 131 broadcast/multicast domain. 133 The above mentioned considerations particularly apply to protocols 134 designed outside the IETF - for two reasons. For one, non-standard 135 protocols will likely not receive operational attention and support 136 in making them more secure such as e.g. DHCP snooping does for DHCP 137 because they typically are not documented. The other reason is that 138 these protocols have been designed in isolation, where a set of 139 considerations to follow is useful in the absence of a larger 140 community providing feedback. In particular, carelessly designed 141 protocols that use broadcast/multicast can break privacy efforts at 142 different layers of the protocol stack such as MAC address or IP 143 address randomization [RFC4941]. 145 1.1. Types and usage of broadcast and multicast 147 In IPv4, two major types of broadcast addresses exist, the limited 148 broadcast which is defined as all-ones (255.255.255.255, defined in 149 section 5.3.5.1 of [RFC1812]) and the directed broadcast with the 150 given network prefix of an IP address and the host part of all-ones 151 (defined in section 5.3.5.2. of [RFC1812]). Broadcast packets are 152 received by all nodes in a subnetwork. Limited broadcasts never 153 transit a router. The same is true for directed broadcasts by 154 default, but routers MAY provide an option to do this [RFC2644]. 155 IPv6 on the other hand does not provide broadcast addresses but 156 solely relies on multicast [RFC4291]. 158 In contrast to broadcast addresses, multicast addresses represent an 159 identifier for a set of interfaces that can be a set different from 160 all nodes in the subnetwork. All interfaces that are identified by a 161 given multicast address receive packets destined towards that address 162 and are called a multicast group. In both IPv4 and IPv6, multiple 163 pre-defined multicast addresses exist. The ones most relevant for 164 this document are the ones with subnet scope. For IPv4, an IP prefix 165 is reserved for this purpose called the Local Network Control Block 166 (224.0.0.0/24, defined in section 4 of [RFC5771]). For IPv6, the 167 relevant multicast addresses are the two All Nodes Addresses, which 168 every IPv6-capable host is required to recognize as identifying 169 itself (see section 2.7.1 of [RFC4291]). 171 Typical usage of these addresses include local service discovery 172 (e.g. mDNS [RFC6762] and LLMNR [RFC4795] make use of multicast), 173 autoconfiguration (e.g. DHCPv4 [RFC2131] uses broadcasts and DHCPv6 174 [RFC3315] uses multicast addresses) and other vital network services 175 such as address resolution or duplicate address detection. But 176 besides these core network functions, also applications make use of 177 broadcast and multicast functionality, often implementing proprietary 178 protocols. In sum, these protocols distribute a diverse set of 179 potentially privacy sensitive information to a large receiver group. 180 To become a receiver, the only requirement is to be part of the same 181 subnetwork. 183 1.2. Requirements Language 185 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 186 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 187 document are to be interpreted as described in RFC 2119 [RFC2119]. 189 2. Privacy considerations 191 There are a few obvious and a few not necessarily obvious things 192 designers of protocols utilizing broadcast/multicast should consider 193 in respect to the privacy implications of their protocol. Most of 194 these items are based on protocol behavior observed as part of 195 experiments on operational networks [TRAC2016]. 197 2.1. Message frequency 199 Frequent broadcast/multicast traffic caused by an application can 200 give away user behavior and online connection times. This allows a 201 passive observer to potentially deduce a user's current activity 202 (e.g. a game) and it allows to create an online profile (i.e. times 203 the user is on the network). The higher the frequency of these 204 messages and the duration of time these messages are sent, the more 205 accurate this profile will be. Given that broadcasts/multicasts are 206 only visible in the same broadcast/multicast domain, these messages 207 also give the rough location of the user away (e.g. a campus or 208 building). 210 This behavior has e.g. been observed by a synchronization mechanism 211 of a popular application, where multiple messages have been sent per 212 minute via broadcast. Given this behavior, it is possible to record 213 a device's time on the network with a sub-minute accuracy given only 214 the traffic of this single application installed on the device. But 215 also services used for local name resolution in modern operating 216 systems utilize broadcast/multicast protocols (e.g. mDNS, LLMNR or 217 NetBIOS) to announce for example their shares regularly and allow a 218 tracking of the online time of a device. 220 If a protocol relies on frequent or periodic broadcast/multicast 221 messages, the frequency SHOULD be chosen conservatively, in 222 particular if the messages contain persistent identifiers (see next 223 subsection). Also, intelligent message suppression mechanisms such 224 as the ones employed in mDNS [RFC6762] SHOULD be implemented. The 225 lower the frequency of broadcast messages, the harder passive traffic 226 analysis and surveillance becomes. 228 2.2. Persistent identifiers 230 A few protocols that make use of broadcast/multicast messages 231 observed in the wild make use of persistent identifiers. This 232 includes the use of host names or more abstract persistent 233 identifiers such as a universally unique identifiers (UUID) or 234 similar. These IDs, which e.g. identify the installation of a 235 certain application might not change across updates of the software 236 and are therefore extremely long lived. This allows a passive 237 observer to track a user precisely if broadcast/multicast messages 238 are frequent. This is even true in case the IP and/or MAC address 239 changes. Such identifiers also allow two different interfaces (e.g. 240 WiFi and Ethernet) to be correlated to the same device. If the 241 application makes use of persistent identifiers for multiple 242 installations of the same application for the same user, this even 243 allows to infer that different devices belong to the same user. 245 The aforementioned broadcast messages from a synchronization 246 mechanism of a popular application also included a persistent 247 identifier in every broadcast. This identifier did never change 248 after the application was installed and allowed to track a device 249 even when it changed its network interface or when it connected to a 250 different network. 252 Persistent IDs are considered bad practice in general for broadcast 253 and multicast communication, as persistent application layer IDs will 254 make efforts on lower layers to randomize identifiers (e.g. 255 [I-D.huitema-6man-random-addresses]) useless. When protocols that 256 make use of broadcast/multicast need to make use of IDs, frequent 257 rotations of these IDs SHOULD be considered to make user tracking 258 more difficult. 260 2.3. Anticipate user behavior 262 A large number of users name their device after themselves, either 263 using their first name, last name or both. Often a host name 264 includes the type, model or maker of a device, its function or 265 includes language specific information. Based on data gathered 266 during experiments performed at IETF meetings and at a large campus 267 network, this appears currently to be prevalent user behavior 268 [TRAC2016]. For protocols using the host name as part of the 269 messages, this clearly will reveal personally identifiable 270 information to everyone on the local network. This information can 271 also be used to mount more sophisticated attacks, when e.g. the owner 272 of a device is identified (as an interesting target) or properties of 273 the device are known (e.g. known vulnerabilities). 275 Some of the most commonly used operating systems include the name the 276 user chooses for the user account during the installation process as 277 part of the host name of the device. The name of the operating 278 system can also be included, revealing therefore two pieces of 279 information, which can be regarded as private information if the host 280 name is used in broadcast/multicast messages. 282 Where possible, the use of host names and other user-provided 283 information in protocols making use of broadcast/multicast SHOULD be 284 avoided. If all that is required is a persistent identifier (which 285 SHOULD be avoided, see Section 2.2), this SHOULD be generated 286 randomly. An application might want to display the information it 287 will broadcast on the LAN at install/config time, so the user is at 288 least aware of the application's behavior. More host name 289 considerations can be found in [RFC8117]. More information on user 290 participation can be found in RFC 6973 [RFC6973]. 292 2.4. Consider potential correlation 294 A large number of services and applications make use of the 295 broadcast/multicast mechanism. That means there are various sources 296 of information that are easily accessible by a passive observer. In 297 isolation, the information these protocols reveal might seem 298 harmless, but given multiple such protocols, it might be possible to 299 correlate this information. E.g. a protocol that uses frequent 300 messages including a UUID to identify the particular installation 301 does not give the identity of the user away. But a single message 302 including the user's host name might just do that and it can be 303 correlated using e.g. the MAC address of the device's interface. 305 In the experiments described in [TRAC2016], it was possible to 306 correlate frequently sent broadcast messages that included a unique 307 identifier with other broadcast/multicast messages containing 308 usernames (e.g. mDNS, LLMNR or NetBIOS), but also relationships to 309 other users. This allowed to reveal the real identity of the users 310 of many devices but it also gave some information about their social 311 environment away. 313 A designer of a protocol that makes use of broadcast/multicast needs 314 to be aware of the fact that even if - in isolation - the information 315 a protocol leaks seems harmless, there might be ways to correlate 316 that information with information from other protocols to reveal 317 sensitive information about a user. 319 2.5. Configurability 321 A lot of applications and services relying on broadcast/multicast 322 protocols do not include the means to declare "safe" environments 323 (e.g. based on the SSID of a WiFi network and the MAC addresses of 324 the access points). E.g. a device connected to a public WiFi will 325 likely broadcast the same information as when connected to the home 326 network. It would be beneficial if certain behavior could be 327 restricted to "safe" environments. 329 A popular operating system e.g. allows the user to specify the trust 330 level of the network the device connects to, which for example 331 restricts specific system services (using broadcast/multicast 332 messages for their normal operation) to be used in trusted networks 333 only. Such functionality could implemented as part of an 334 application. 336 An application developer making use of broadcasts/multicasts as part 337 of the application SHOULD make the broadcast feature, if possible, 338 configurable, so that potentially sensitive information does not leak 339 on public networks, where the threat to privacy is much larger. 341 3. Operational considerations 343 Besides changing end-user behavior, choosing sensible defaults as an 344 operating system vendor (e.g. for suggesting host names) and the 345 considerations for protocol designers mentioned in this document, 346 there are things that the network administrators/operators can do to 347 limit the above mentioned problems. 349 A feature not uncommonly found on access points e.g. is to filter 350 broadcast and multicast traffic. This will potentially break certain 351 applications or some of their functionality but will also protect the 352 users from potentially leaking sensitive information. 354 4. Summary 356 Increasingly, applications rely on protocols that send and receive 357 broadcast and multicast messages. For some, broadcasts/multicasts 358 are the basis of their application logic, others use broadcasts/ 359 multicasts to improve certain aspects of the application but are 360 fully functional in case broadcasts/multicasts fail. Irrespective of 361 the role of broadcast and multicast messages for the application, the 362 designers of protocols that make use of them should be very careful 363 in their protocol design because of the special nature of broadcast 364 and multicast. 366 It is not always possible to implement certain functionality via 367 unicast, but in case a protocol designer chooses to rely on 368 broadcast/multicast, the following should be carefully considered: 370 o IETF-specified protocols, such as mDNS [RFC6762], SHOULD be used 371 if possible as operational support might exist to protect against 372 the leakage of private information. Also, for some protocols 373 privacy extensions are being specified, which can be used if 374 implemented. E.g. for DNS-SD privacy extensions are documented in 375 [I-D.ietf-dnssd-privacy] 377 o Using user-specified information inside broadcast/multicast 378 messages SHOULD be avoided, as users will often use personal 379 information or other information aiding attackers, in particular 380 if the user is unaware about how that information is being used 382 o The use of persistent IDs in messages SHOULD be avoided, as this 383 allows user tracking, correlation and potentially has a 384 devastating effect on other privacy protection mechanisms 386 o If one really must design a new protocol relying on broadcast/ 387 multicast and cannot use an IETF-specified protocol, then: 389 * the protocol SHOULD be very conservative in how frequently it 390 sends messages as an effort in data minimization 392 * it SHOULD make use of mechanisms implemented in IETF-specified 393 protocols that can be helpful in privacy protection such as 394 message suppression in mDNS 396 * it SHOULD be designed in a way that information sent in 397 broadcast/multicast messages cannot be correlated with 398 information from other protocols using broadcast/multicast 400 * it SHOULD be possible to let the user configure "safe" 401 environments if possible (e.g. based on the SSID) to minimize 402 the risk of information leakage (e.g. a home network as opposed 403 to a public Wifi) 405 5. Other considerations 407 Besides privacy implications, frequent broadcasting also represents a 408 performance problem. In particular in certain wireless technologies 409 such as 802.11, broadcast and multicast are transmitted at a much 410 lower rate (the lowest common denominator rate) compared to unicast 411 and therefore have a much bigger impact on the overall available 412 airtime [I-D.perkins-intarea-multicast-ieee802]. Further, it will 413 limit the ability for devices to go to sleep if frequent broadcasts 414 are being sent. A similar problem in respect to Router 415 Advertisements is addressed in 416 [I-D.ietf-v6ops-reducing-ra-energy-consumption]. In that respect 417 broadcasts/multicast can be used for another class of attacks that is 418 not related to privacy. The potential impact on network performance 419 should nevertheless be considered when designing a protocol that 420 makes use of broadcast/multicast. 422 6. Acknowledgments 424 We would like to thank Eliot Lear, Joe Touch and Stephane Bortzmeyer 425 for their valuable input to this document. 427 This work was partly supported by the European Commission under grant 428 agreement FP7-318627 mPlane. Support does not imply endorsement. 430 7. IANA Considerations 432 This memo includes no request to IANA. 434 8. Security Considerations 436 This document deals with privacy-related considerations of broadcast- 437 and multicast-based protocols. It contains advice for designers of 438 such protocols to minimize the leakage of privacy-sensitive 439 information. The intent of the advice is to make sure that 440 identities will remain anonymous and user tracking will be made 441 difficult. 443 It should be noted that certain applications could make use of 444 existing mechanisms to protect multicast traffic such as the ones 445 defined in [RFC5374]. Examples of such applications can be found in 446 Appendix A. of [RFC5374]. Given the required infrastructure and 447 assumptions about these applications and the security infrastructure, 448 many applications will not be able to make use of such mechanisms. 450 9. References 452 9.1. Normative References 454 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 455 Requirement Levels", BCP 14, RFC 2119, March 1997. 457 9.2. Informative References 459 [I-D.huitema-6man-random-addresses] 460 Huitema, C., "Implications of Randomized Link Layers 461 Addresses for IPv6 Address Assignment", draft-huitema- 462 6man-random-addresses-03 (work in progress), March 2016. 464 [I-D.ietf-dnssd-privacy] 465 Huitema, C. and D. Kaiser, "Privacy Extensions for DNS- 466 SD", draft-ietf-dnssd-privacy-00 (work in progress), 467 October 2016. 469 [I-D.ietf-v6ops-reducing-ra-energy-consumption] 470 Yourtchenko, A. and L. Colitti, "Reducing energy 471 consumption of Router Advertisements", draft-ietf-v6ops- 472 reducing-ra-energy-consumption-03 (work in progress), 473 November 2015. 475 [I-D.perkins-intarea-multicast-ieee802] 476 Perkins, C., Stanley, D., Kumari, W., and J. Zuniga, 477 "Multicast Considerations over IEEE 802 Wireless Media", 478 draft-perkins-intarea-multicast-ieee802-03 (work in 479 progress), July 2017. 481 [RFC0919] Mogul, J., "Broadcasting Internet Datagrams", STD 5, RFC 482 919, DOI 10.17487/RFC0919, October 1984, 483 . 485 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 486 RFC 1812, DOI 10.17487/RFC1812, June 1995, 487 . 489 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 490 2131, DOI 10.17487/RFC2131, March 1997, 491 . 493 [RFC2644] Senie, D., "Changing the Default for Directed Broadcasts 494 in Routers", BCP 34, RFC 2644, DOI 10.17487/RFC2644, 495 August 1999, . 497 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 498 C., and M. Carney, "Dynamic Host Configuration Protocol 499 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 500 2003, . 502 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 503 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 504 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 505 RFC 3819, DOI 10.17487/RFC3819, July 2004, 506 . 508 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 509 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 510 2006, . 512 [RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local 513 Multicast Name Resolution (LLMNR)", RFC 4795, DOI 514 10.17487/RFC4795, January 2007, 515 . 517 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 518 Extensions for Stateless Address Autoconfiguration in 519 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 520 . 522 [RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast 523 Extensions to the Security Architecture for the Internet 524 Protocol", RFC 5374, DOI 10.17487/RFC5374, November 2008, 525 . 527 [RFC5771] Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines for 528 IPv4 Multicast Address Assignments", BCP 51, RFC 5771, DOI 529 10.17487/RFC5771, March 2010, 530 . 532 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, 533 DOI 10.17487/RFC6762, February 2013, 534 . 536 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 537 Morris, J., Hansen, M., and R. Smith, "Privacy 538 Considerations for Internet Protocols", RFC 6973, DOI 539 10.17487/RFC6973, July 2013, 540 . 542 [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy 543 Considerations for IPv6 Address Generation Mechanisms", 544 RFC 7721, DOI 10.17487/RFC7721, March 2016, 545 . 547 [RFC7819] Jiang, S., Krishnan, S., and T. Mrugalski, "Privacy 548 Considerations for DHCP", RFC 7819, DOI 10.17487/RFC7819, 549 April 2016, . 551 [RFC8117] Huitema, C., Thaler, D., and R. Winter, "Current Hostname 552 Practice Considered Harmful", RFC 8117, DOI 10.17487/ 553 RFC8117, March 2017, . 556 [TRAC2016] 557 Faath, M., Weisshaar, F., and R. Winter, "How Broadcast 558 Data Reveals Your Identity and Social Graph", 7th 559 International Workshop on TRaffic Analysis and 560 Characterization IEEE TRAC 2016, September 2016. 562 Authors' Addresses 564 Rolf Winter 565 University of Applied Sciences Augsburg 566 Augsburg 567 DE 569 Email: rolf.winter@hs-augsburg.de 570 Michael Faath 571 Conntac GmbH 572 Augsburg 573 DE 575 Email: faath@conntac.net 577 Fabian Weisshaar 578 University of Applied Sciences Augsburg 579 Augsburg 580 DE 582 Email: fabian.weisshaar@hs-augsburg.de