draft-ietf-intarea-broadcast-consider-00.txt   draft-ietf-intarea-broadcast-consider-01.txt 
Internet Engineering Task Force R. Winter Internet Engineering Task Force R. Winter
Internet-Draft M. Faath Internet-Draft M. Faath
Intended status: Informational F. Weisshaar Intended status: Informational F. Weisshaar
Expires: May 4, 2017 University of Applied Sciences Augsburg Expires: May 4, 2017 University of Applied Sciences Augsburg
October 31, 2016 October 31, 2016
Privacy considerations for IP broadcast and multicast protocol designers Privacy considerations for IP broadcast and multicast protocol designers
draft-ietf-intarea-broadcast-consider-00 draft-ietf-intarea-broadcast-consider-01
Abstract Abstract
A number of application-layer protocols make use of IP broadcasts or A number of application-layer protocols make use of IP broadcasts or
multicast messages for functions such as local service discovery or multicast messages for functions like local service discovery or name
name resolution. Some of these functions can only be implemented resolution. Some of these functions can only be implemented
efficiently using such mechanisms. When using broadcasts or efficiently using such mechanisms. When using broadcasts or
multicast messages, a passive observer in the same broadcast domain multicast messages, a passive observer in the same broadcast/
can trivially record these messages and analyze their content. multicast domain can trivially record these messages and analyze
Therefore, broadcast/multicast protocol designers need to take their content. Therefore, broadcast/multicast protocol designers
special care when designing their protocols. need to take special care when designing their protocols.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
skipping to change at page 2, line 14 skipping to change at page 2, line 14
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Privacy considerations . . . . . . . . . . . . . . . . . . . 3 2. Privacy considerations . . . . . . . . . . . . . . . . . . . 3
2.1. Message frequency . . . . . . . . . . . . . . . . . . . . 3 2.1. Message frequency . . . . . . . . . . . . . . . . . . . . 4
2.2. Persistent identifiers . . . . . . . . . . . . . . . . . 4 2.2. Persistent identifiers . . . . . . . . . . . . . . . . . 4
2.3. Anticipate user behaviour . . . . . . . . . . . . . . . . 4 2.3. Anticipate user behavior . . . . . . . . . . . . . . . . 5
2.4. Consider potential correlation . . . . . . . . . . . . . 5 2.4. Consider potential correlation . . . . . . . . . . . . . 5
2.5. Configurability . . . . . . . . . . . . . . . . . . . . . 5 2.5. Configurability . . . . . . . . . . . . . . . . . . . . . 6
3. Operational considerations . . . . . . . . . . . . . . . . . 5 3. Operational considerations . . . . . . . . . . . . . . . . . 7
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. Other considerations . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
7. Informative References . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
Broadcast and multicast messages have a large receiver group by Broadcast and multicast messages have a large (and to the sender
design. Because of that, these two mechanisms are vital for a number unknown) receiver group by design. Because of that, these two
of basic network functions such as auto-configuration. Application mechanisms are vital for a number of basic network functions such as
developers use broadcast/multicast messages to implement things like auto-configuration. Application developers use broadcast/multicast
local service or peer discovery and it appears that an increasing messages to implement things like local service or peer discovery and
number of applications make use of it [TRAC2016]. it appears that an increasing number of applications make use of it.
And, as RFC 919 [RFC0919] puts it, "The use of broadcasts [...] is a
good base for many applications".
Using broadcast/multicast can become problematic if the information Using broadcast/multicast can become problematic if the information
that is being distributed can be regarded as sensitive or when the that is being distributed can be regarded as sensitive or when the
information that is distributed by multiple of these protocols can be information that is distributed by multiple of these protocols can be
correlated in a way that sensitive data can be derived. This is correlated in a way that sensitive data can be derived. This is
clearly true for any protocol, but broadcast/multicast is special in clearly true for any protocol, but broadcast/multicast is special in
at least two respects: a) the aforementioned large receiver group at least two respects:
which makes it trivial for anybody on a LAN to collect the
information without special privileges or a special location in the (a) The aforementioned large receiver group, consisting of receivers
network and b) encryption is more difficult when broadcasting/ unknown to the sender. This makes eavesdropping without special
multicasting messages. privileges or a special location in the network trivial for
anybody in the broadcast/multicast domain.
(b) Encryption is more difficult when broadcast/multicast messages,
leaving content of these messages in the clear and making it
easier to spoof and replay them.
Given the above, privacy protection for protocols based on broadcast
or multicast communication is significantly more difficult compared
to unicast communication and at the same time invading the privacy is
much easier.
Privacy considerations of IETF-specified protocols have received some Privacy considerations of IETF-specified protocols have received some
attention in the recent past(e.g. [RFC7721] or attention in the recent past (e.g. RFC 7721 [RFC7721] or RFC 7919
[I-D.ietf-dhc-dhcp-privacy]). This draft documents a number of [RFC7819]). There is also general guidance available for document
privacy considerations for broadcast/multicast protocol designers authors on when and how to include a privacy considerations section
that are intended to reduce the likelihood that a broadcast protocol in their documents and on how to evaluate the privacy implications of
can be misused to collect sensitive data about devices, users and Internet protocols [RFC6973]. RFC6973 also describes potential
groups of users on a LAN. These considerations particularly apply to threats to privacy in great detail and lists terminology that is also
protocols designed outside the IETF for two reasons. For one, non- used in this document.
standard protocols will likely not receive operational attention and
support in making them more secure such as e.g. DHCP snooping does In contrast to RFC6973, this document contains a number of privacy
for DHCP because they typically are not documented. The other reason considerations especially for broadcast/multicast protocol designers
is that these protocols have been designed in isolation, where a set that are intended to reduce the likelihood that a broadcast/multicast
of considerations to follow is useful in the absence of a larger protocol can be misused to collect sensitive data about devices,
users and groups of users on a broadcast/multicast domain. These
considerations particularly apply to protocols designed outside the
IETF for two reasons. For one, non-standard protocols will likely
not receive operational attention and support in making them more
secure such as e.g. DHCP snooping does for DHCP because they
typically are not documented. The other reason is that these
protocols have been designed in isolation, where a set of
considerations to follow is useful in the absence of a larger
community providing feedback. In particular, carelessly designed community providing feedback. In particular, carelessly designed
broadcast/multicast protocols can break privacy efforts at different broadcast/multicast protocols can break privacy efforts at different
layers of the protocol stack such as MAC address or IP address layers of the protocol stack such as MAC address or IP address
randomization [RFC4941]. randomization [RFC4941].
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Privacy considerations 2. Privacy considerations
There are a few obvious and a few not necessarily obvious things There are a few obvious and a few not necessarily obvious things
designers of broadcast/multicast protocols should consider in respect designers of broadcast/multicast protocols should consider in respect
to the privacy implications of their protocol. Most of these items to the privacy implications of their protocol. Most of these items
are based on protocol behaviour observed as part of experiments on are based on protocol behavior observed as part of experiments on
operational networks [TRAC2016]. operational networks [TRAC2016].
2.1. Message frequency 2.1. Message frequency
Frequent broadcast/multicast traffic caused by an application can Frequent broadcast/multicast traffic caused by an application can
give user behaviour and online times away. This allows a passive give user behavior and online times away. This allows a passive
observer to potentially deduce a user's current activity (e.g. a observer to potentially deduce a user's current activity (e.g. a
game) and it allows to create an online profile (i.e. times the user game) and it allows to create an online profile (i.e. times the user
is on the network). The higher the frequency of these messages, the is on the network). The higher the frequency of these messages, the
more accurate this profile will be. Given that broadcasts are only more accurate this profile will be. Given that broadcasts/multicasts
visible in the same broadcast domain, these messages also give the are only visible in the same broadcast/multicast domain, these
rough location of the user away (e.g. a campus or building). messages also give the rough location of the user away (e.g. a campus
or building).
Besides the privacy implications of frequent broadcasting, it also This behavior has e.g. been observed by a synchronization mechanism
represents a performance problem. In particular in certain wireless of a popular application, where multiple messages have been sent per
technologies such as 802.11, broadcast and multicast are transmitted minute via broadcast. Given this behavior, it is possible to record
at a much lower rate (the lowest common denominator rate) compared to a device's time on the network with a sub-minute accuracy given only
unicast and therefore have a much bigger impact on the overall the traffic of this single application installed on the device. But
available airtime. Further, it will limit the ability for devices to also services used for local name resolution in modern operating
go to sleep if frequent broadcasts are being sent. A similar problem systems utilize broadcast/multicast protocols (e.g. mDNS, LLMNR or
in respect to Router Advertisements is addressed in NetBIOS) to announce for example their shares regularly and allow a
[I-D.ietf-v6ops-reducing-ra-energy-consumption]. tracking of the online time of a device.
If a protocol relies on frequent or periodic broadcast/multicast If a protocol relies on frequent or periodic broadcast/multicast
messages, the frequency SHOULD be chosen conservatively, in messages, the frequency SHOULD be chosen conservatively, in
particular if the messages contain persistent identifiers (see next particular if the messages contain persistent identifiers (see next
subsection). Also, intelligent message suppression mechanisms such subsection). Also, intelligent message suppression mechanisms such
as the ones employed in mDNS [RFC6762] SHOULD be implemented. as the ones employed in mDNS [RFC6762] SHOULD be implemented. The
lower the frequency of broadcast messages, the harder traffic
analysis and surveillance becomes.
2.2. Persistent identifiers 2.2. Persistent identifiers
A few broadcast/multicast protocols observed in the wild make use of A few broadcast/multicast protocols observed in the wild make use of
persistent identifiers. This includes the use of hostnames or more persistent identifiers. This includes the use of host names or more
abstract persistent identifiers such as a UUID or similar. These abstract persistent identifiers such as a UUID or similar. These
IDs, which e.g. identify the installation of a certain application IDs, which e.g. identify the installation of a certain application
might not change across updates of the software and are therefore might not change across updates of the software and are therefore
extremely long lived. This allows a passive observer to track a user extremely long lived. This allows a passive observer to track a user
precisely if broadcast/multicast messages are frequent. This is even precisely if broadcast/multicast messages are frequent. This is even
true in case the IP and/or MAC address changes. Such identifiers true in case the IP and/or MAC address changes. Such identifiers
also allow two different interfaces (e.g. Wifi and Ethernet) to be also allow two different interfaces (e.g. WiFi and Ethernet) to be
correlated to the same device. If the application makes use of correlated to the same device. If the application makes use of
persistent identifiers for multiple installations of the same persistent identifiers for multiple installations of the same
application for the same user, this even allows to infer that application for the same user, this even allows to infer that
different devices belong to the same user. different devices belong to the same user.
The aforementioned broadcast messages from a synchronization
mechanism of a popular application also included a persistent
identifier in every broadcast. This identifier did never change
after the application was installaed and allowed to track a device
even when it changed its network interface or when it connected to a
different network.
If a broadcast/multicast protocol relies on IDs to be transmitted, it If a broadcast/multicast protocol relies on IDs to be transmitted, it
SHOULD be considered if frequent ID rotations are possible in order SHOULD be considered if frequent ID rotations are possible in order
to make user tracking more difficult. Persistent IDs are considered to make user tracking more difficult. Persistent IDs are considered
bad practice in general as persistent application layer IDs will make bad practice in general for broadcast and multicast communication as
efforts on lower layers to randomize identifiers (e.g. persistent application layer IDs will make efforts on lower layers to
[I-D.huitema-6man-random-addresses]) useless or at least much more randomize identifiers (e.g. [I-D.huitema-6man-random-addresses])
difficult. useless or at least much more difficult.
2.3. Anticipate user behaviour 2.3. Anticipate user behavior
A large number of users name their device after themselves, either A large number of users name their device after themselves, either
using their first name, last name or both. Often a hostname includes using their first name, last name or both. Often a host name
the type, model or maker of a device, its function or includes includes the type, model or maker of a device, its function or
language specific information. Based on gathered data, this appears includes language specific information. Based on gathered data, this
currently to be prevalent user behaviour [TRAC2016]. For protocols appears currently to be prevalent user behavior [TRAC2016]. For
using the hostname as part of the messages, this clearly will reveal protocols using the host name as part of the messages, this clearly
personally identifiable information to everyone on the local network. will reveal personally identifiable information to everyone on the
local network. This information can also be used to mount more
sophisticated attacks, when e.g. the owner of a device is identified
(as an interesting target) or properties of the device are known
(e.g. known vulnerabilities).
Where possible, the use of hostnames in broadcast/multicast protocols A popular operating system vendor includes the name the user chooses
SHOULD be avoided. If only a persistent ID is needed, this can be for the user account during the installation process as part of the
generated. An application might want to display the information it host name of the device. The name of the operating system is also
will broadcast on the LAN at install/config time, so the user is at included, revealing therefore two pieces of information, which can be
least aware of the application's behaviour. More hostname regarded as private information if the host name is used in
considerations can be found in [I-D.ietf-intarea-hostname-practice]. broadcast/multicast messages.
Where possible, the use of host names and other user provided
information in broadcast/multicast protocols SHOULD be avoided. If
only a persistent ID is needed, this can be generated. An
application might want to display the information it will broadcast
on the LAN at install/config time, so the user is at least aware of
the application's behavior. More host name considerations can be
found in [I-D.ietf-intarea-hostname-practice]. More information on
user participation can be found in RFC 6973 [RFC6973].
2.4. Consider potential correlation 2.4. Consider potential correlation
A large number of services and applications make use of the A large number of services and applications make use of the
broadcast/multicast mechanism. That means there are various sources broadcast/multicast mechanism. That means there are various sources
of information that are easily accessible by a passive observer. In of information that are easily accessible by a passive observer. In
isolation, the information these protocols reveal might seem isolation, the information these protocols reveal might seem
harmless, but given multiple such protocols, it might be possible to harmless, but given multiple such protocols, it might be possible to
correlate this information. E.g. a protocol that uses frequent correlate this information. E.g. a protocol that uses frequent
messages including a UUID to identify the particular installation messages including a UUID to identify the particular installation
does not give the identity of the user away. But a single message does not give the identity of the user away. But a single message
including the user's hostname might just do that and it can be including the user's host name might just do that and it can be
correlated using e.g. the MAC address of the device's interface. correlated using e.g. the MAC address of the device's interface.
In the experiments described in [TRAC2016], it was possible to
correlate frequently sent broadcast messages that included a unique
identifier with other broadcast/multicast messages containing
usernames (e.g. mDNS, LLMNR or NetBIOS), but also relationships to
other users. This allowed to reveal the real identity of the users
of many devices but it also gave some information about their social
environment away.
A broadcast protocol designer should be aware of the fact that even A broadcast protocol designer should be aware of the fact that even
if - in isolation - the information a protocol leaks seems harmless, if - in isolation - the information a protocol leaks seems harmless,
there might be ways to correlate that information with other there might be ways to correlate that information with other
broadcast protocol information to reveal sensitive information about broadcast protocol information to reveal sensitive information about
a user. a user.
2.5. Configurability 2.5. Configurability
A lot of applications and services using broadcast protocols do not A lot of applications and services using broadcast/multicast
include the means to declare "safe" environments (e.g. based on the protocols do not include the means to declare "safe" environments
SSID of a WiFi network). E.g. a device connected to a public WiFi (e.g. based on the SSID of a WiFi network and the MAC addresses of
will likely broadcast the same information as when connected to the the access points). E.g. a device connected to a public WiFi will
home network. It would be beneficial if certain behaviour could be likely broadcast the same information as when connected to the home
network. It would be beneficial if certain behavior could be
restricted to "safe" environments. restricted to "safe" environments.
An application developer making use of broadcasts as part of the A popular operating system e.g. allows the user to specify the trust
application SHOULD make the broadcast feature, if possible, level of the network the device connects to, which for example
restricts specific system services (using broadcast/multicast
messages for their normal operation) to be used in untrusted
networks. Such functionality could implemented as part of an
application.
An application developer making use of broadcasts/multicasts as part
of the application SHOULD make the broadcast feature, if possible,
configurable, so that potentially sensitive information does not leak configurable, so that potentially sensitive information does not leak
on public networks. on public networks, where the thread to privacy is much larger.
3. Operational considerations 3. Operational considerations
Besides changing end-user behavior, choosing sensible defaults as an Besides changing end-user behavior, choosing sensible defaults as an
operating system vendor (e.g. for suggesting host names) and the operating system vendor (e.g. for suggesting host names) and the
considerations for protocol designers mentioned in this document, considerations for protocol designers mentioned in this document,
there are things that the network administrators/operators can do to there are things that the network administrators/operators can do to
limit the above mentioned problems. limit the above mentioned problems.
A feature not uncommonly found on access points e.g. is to filter A feature not uncommonly found on access points e.g. is to filter
broadcast and multicast traffic. This will potentially break certain broadcast and multicast traffic. This will potentially break certain
applications or some of their functionality but will also protect the applications or some of their functionality but will also protect the
users from potentially leaking sensitive information. users from potentially leaking sensitive information.
4. Acknowledgements 4. Summary
Increasingly, applications rely on broadcast and multicast messages.
For some, broadcasts/multicasts are the basis of their application
logic, others use broadcasts/multicasts to improve certain aspects of
the application but are fully functional in case broadcasts/
multicasts fail. Irrespective of the role of broadcast and multicast
messages for the application, the designers of protocols that make
use of them should be very careful in their protocol design because
of the special nature of broad- and multicast.
It is not always possible to implement certain functionality via
unicast, but in case a protocol designer chooses to rely on
broadcast/multicast, the following should be carefully considered:
o IETF-specified protocols, such as mDNS [RFC6762], should be used
if possible as operational support might exist to protect against
the leakage of private information
o Avoid using user-specified information inside broadcast/multicast
messages as users will often use personal information or other
information aiding attackers, in particular if the user is unaware
about how that information is being used
o Avoid persistent IDs in messages as this allows user tracking,
correlation and potentially has a devastating effect on other
privacy protection mechanisms
o If you really must use a broadcast/multicast protocol and cannot
use an IETF-specified protocol, then:
* Be very conservative in how frequently you send messages as an
effort in data minimization
* Seek advice from IETF-specifies protocols such as message
suppression in mDNS
* Try to design the protocol in a way that the information cannot
be correlated with other information in broadcast/multicast
messages
* Let the user configure safe environments if possible (e.g.
based on the SSID)
[Note: discussions on this document should be take place on the
Intarea mailing list of the IETF. Subscription:
https://www.ietf.org/mailman/listinfo/int-area, Mailing list archive:
https://www.ietf.org/mail-archive/web/int-area/current/maillist.html]
5. Other considerations
Besides the privacy implications of frequent broadcasting, it also
represents a performance problem. In particular in certain wireless
technologies such as 802.11, broadcast and multicast are transmitted
at a much lower rate (the lowest common denominator rate) compared to
unicast and therefore have a much bigger impact on the overall
available airtime. Further, it will limit the ability for devices to
go to sleep if frequent broadcasts are being sent. A similar problem
in respect to Router Advertisements is addressed in
[I-D.ietf-v6ops-reducing-ra-energy-consumption]. In that respect
broadcasts can be used for another class of attacks that not related
to privacy. The potential impact on network performance should
nevertheless be considered by broadcast protocol designers.
6. Acknowledgments
We would like to thank Eliot Lear and Stephane Bortzmeyer for their
input.
This work was partly supported by the European Commission under grant This work was partly supported by the European Commission under grant
agreement FP7-318627 mPlane. Support does not imply endorsement. agreement FP7-318627 mPlane. Support does not imply endorsement.
5. IANA Considerations 7. IANA Considerations
This memo includes no request to IANA. This memo includes no request to IANA.
6. Security Considerations 8. Security Considerations
This document deals with privacy-related considerations of broadcast- This document deals with privacy-related considerations of broadcast-
and multicast-based protocols. It contains advice for designers of and multicast-based protocols. It contains advice for designers of
such protocols to minimize the leakage of privacy-sensitive such protocols to minimize the leakage of privacy-sensitive
information. The intent of the advice is to make sure that information. The intent of the advice is to make sure that
identities will remain anonymous and user tracking will be made identities will remain anonymous and user tracking will be made
difficult. difficult.
7. Informative References 9. Informative References
[I-D.huitema-6man-random-addresses] [I-D.huitema-6man-random-addresses]
Huitema, C., "Implications of Randomized Link Layers Huitema, C., "Implications of Randomized Link Layers
Addresses for IPv6 Address Assignment", draft-huitema- Addresses for IPv6 Address Assignment", draft-huitema-
6man-random-addresses-03 (work in progress), March 2016. 6man-random-addresses-03 (work in progress), March 2016.
[I-D.ietf-dhc-dhcp-privacy]
Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
considerations for DHCP", draft-ietf-dhc-dhcp-privacy-05
(work in progress), February 2016.
[I-D.ietf-intarea-hostname-practice] [I-D.ietf-intarea-hostname-practice]
Huitema, C. and D. Thaler, "Current Hostname Practice Huitema, C. and D. Thaler, "Current Hostname Practice
Considered Harmful", draft-ietf-intarea-hostname- Considered Harmful", draft-ietf-intarea-hostname-
practice-00 (work in progress), October 2015. practice-00 (work in progress), October 2015.
[I-D.ietf-v6ops-reducing-ra-energy-consumption] [I-D.ietf-v6ops-reducing-ra-energy-consumption]
Yourtchenko, A. and L. Colitti, "Reducing energy Yourtchenko, A. and L. Colitti, "Reducing energy
consumption of Router Advertisements", draft-ietf-v6ops- consumption of Router Advertisements", draft-ietf-v6ops-
reducing-ra-energy-consumption-03 (work in progress), reducing-ra-energy-consumption-03 (work in progress),
November 2015. November 2015.
[RFC0919] Mogul, J., "Broadcasting Internet Datagrams", STD 5, RFC
919, DOI 10.17487/RFC0919, October 1984,
<http://www.rfc-editor.org/info/rfc919>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<http://www.rfc-editor.org/info/rfc4941>. <http://www.rfc-editor.org/info/rfc4941>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013, DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>. <http://www.rfc-editor.org/info/rfc6762>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, DOI
10.17487/RFC6973, July 2013,
<http://www.rfc-editor.org/info/rfc6973>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms", Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016, RFC 7721, DOI 10.17487/RFC7721, March 2016,
<http://www.rfc-editor.org/info/rfc7721>. <http://www.rfc-editor.org/info/rfc7721>.
[RFC7819] Jiang, S., Krishnan, S., and T. Mrugalski, "Privacy
Considerations for DHCP", RFC 7819, DOI 10.17487/RFC7819,
April 2016, <http://www.rfc-editor.org/info/rfc7819>.
[TRAC2016] [TRAC2016]
Faath, M., Weisshaar, F., and R. Winter, "How Broadcast Faath, M., Weisshaar, F., and R. Winter, "How Broadcast
Data Reveals Your Identity and Social Graph", 7th Data Reveals Your Identity and Social Graph", 7th
International Workshop on TRaffic Analysis and International Workshop on TRaffic Analysis and
Characterization IEEE TRAC 2016, September 2016. Characterization IEEE TRAC 2016, September 2016.
Authors' Addresses Authors' Addresses
Rolf Winter Rolf Winter
University of Applied Sciences Augsburg University of Applied Sciences Augsburg
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