💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc6462.txt captured on 2023-12-28 at 17:15:13.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Internet Architecture Board (IAB) A. Cooper
Request for Comments: 6462 January 2012
Category: Informational
ISSN: 2070-1721
Report from the Internet Privacy Workshop
Abstract
On December 8-9, 2010, the IAB co-hosted an Internet privacy workshop
with the World Wide Web Consortium (W3C), the Internet Society
(ISOC), and MIT's Computer Science and Artificial Intelligence
Laboratory (CSAIL). The workshop revealed some of the fundamental
challenges in designing, deploying, and analyzing privacy-protective
Internet protocols and systems. Although workshop participants and
the community as a whole are still far from understanding how best to
systematically address privacy within Internet standards development,
workshop participants identified a number of potential next steps.
For the IETF, these included the creation of a privacy directorate to
review Internet-Drafts, further work on documenting privacy
considerations for protocol developers, and a number of exploratory
efforts concerning fingerprinting and anonymized routing. Potential
action items for the W3C included investigating the formation of a
privacy interest group and formulating guidance about fingerprinting,
referrer headers, data minimization in APIs, usability, and general
considerations for non-browser-based protocols.
Note that this document is a report on the proceedings of the
workshop. The views and positions documented in this report are
those of the workshop participants and do not necessarily reflect the
views of the IAB, W3C, ISOC, or MIT CSAIL.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Architecture Board (IAB)
and represents information that the IAB has deemed valuable to
provide for permanent record. Documents approved for publication by
the IAB are not a candidate for any level of Internet Standard; see
Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6462.
Cooper Informational [Page 1]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction ....................................................3
2. Workshop Overview ...............................................3
2.1. Technical Discussion .......................................4
2.2. SDO Discussion .............................................5
3. Design Challenges ...............................................6
3.1. Ease of Fingerprinting .....................................6
3.2. Information Leakage ........................................7
3.3. Differentiating between First and Third Parties ............8
3.4. Lack of Transparency and User Awareness ....................9
4. Deployment and Analysis Challenges ..............................9
4.1. Generative Protocols vs. Contextual Threats ................9
4.2. Tension between Privacy Protection and Usability ..........11
4.3. Interaction between Business, Legal, and Technical
Incentives ................................................12
4.3.1. Role of Regulation .................................12
4.3.2. P3P: A Case Study of the Importance of Incentives ..13
5. Conclusions and Next Steps .....................................14
5.1. IETF Outlook ..............................................14
5.2. W3C Outlook ...............................................15
5.3. Other Future Work .........................................15
6. Acknowledgements ...............................................15
7. Security Considerations ........................................15
8. Informative References .........................................16
Appendix A. Workshop Materials ....................................19
Appendix B. Workshop Participants .................................19
Appendix C. Accepted Position Papers ..............................21
Cooper Informational [Page 2]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
1. Introduction
On December 8-9, 2010, the IAB co-hosted a workshop with the W3C,
ISOC, and MIT's Computer Science and Artificial Intelligence
Laboratory (CSAIL) about Internet privacy [Workshop]. The workshop
was organized to help the Internet community gain some understanding
of what it means for Internet-based systems to respect privacy, how
such systems have been or could be designed, how the relationship
between the web and the broader Internet impacts privacy, and what
specific work the IETF and/or the W3C might pursue to address
Internet privacy. An overview of topics discussed at the workshop is
provided in Section 2.
The workshop discussions revealed the complexity and broad-based
nature of privacy on the Internet. Across numerous different
applications, a number of fundamental design challenges appear again
and again: the increasing ease of user/device/application
fingerprinting, unforeseen information leakage, difficulties in
distinguishing first parties from third parties, complications
arising from system dependencies, and the lack of transparency and
user awareness of privacy risks and tradeoffs (see Section 3).
Workshop participants also identified a number of barriers to
successful deployment and analysis of privacy-minded protocols and
systems, including the difficulty of using generic protocols and
tools to defend against context-specific threats; the tension between
privacy protection and usability; and the difficulty of navigating
between business, legal, and individual incentives (see Section 4).
Privacy challenges far outnumber solutions, but the workshop
identified a number of concrete preliminary steps that standards
organizations can take to help ensure respect for user privacy in the
design of future standards and systems. For the IETF, these included
the creation of a privacy directorate to review Internet-Drafts,
further work on documenting privacy considerations for protocol
developers, and initiating a number of exploratory efforts concerning
fingerprinting and anonymized routing. Potential action items for
the W3C included investigating the formation of a privacy interest
group and formulating guidance about fingerprinting, referrer
headers, data minimization in APIs, usability, and general
considerations for non-browser-based protocols. These next steps and
workshop outcomes are discussed in Section 5.
2. Workshop Overview
The workshop explored both current technical challenges to protecting
privacy and the ways in which standards organizations can help to
address those challenges. Links to workshop materials are listed in
Appendix A.
Cooper Informational [Page 3]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
2.1. Technical Discussion
The workshop explored privacy challenges in three different technical
domains: at the network level, at the browser level, and with respect
to cross-site data exchanges. Example technologies were highlighted
in each area to motivate the discussion.
At the network level, participants discussed IP address hiding in
mobility protocols, privacy extensions for IPv6 addressing [RFC4941],
and onion routing. Discussion about the Tor project [Tor] was
particularly insightful. Tor is a circuit-based, low-latency
communication service designed to anonymize protocols that run over
TCP. End hosts participating in a Tor exchange choose a path through
the network and build a circuit in which each "onion router" in the
path knows its predecessor and successor, but no other nodes in the
circuit. Each onion router in the path unwraps and decrypts received
information before relaying it downstream.
For Tor to provide anonymity guarantees, Tor nodes need to be able to
strip out information elements that can be used to re-identify users
over time. For example, web technologies such as cookies, large
portions of JavaScript, and almost all browser plug-ins (including
Flash) need to be disabled in order to maintain Tor's privacy
properties during web use, significantly hampering usability.
At the browser level, the discussion focused first on experiences
with "private browsing" modes. Private browsing puts a browser into
a temporary session where no information about the user's browsing
session is stored locally after the session ends. The goal is to
protect the user's browsing behavior from others who may make use of
the same browser on the same machine. Private browsing is not
designed to protect the user from being tracked by malware (e.g.,
keyloggers), remote servers, employers, or governments, but there is
some evidence that users fail to understand the distinction between
protection from snooping among users who share a device and these
other forms of tracking. The specific protections offered by private
browsing modes also vary from browser to browser, creating privacy
loopholes in some cases.
The browser discussion also addressed proposals for "Do Not Track"
(DNT) technologies to be built into browsers to provide users with a
simple way to opt out of web tracking. At the time of the workshop,
various different technical proposals had been designed to offer
users the ability to indicate their preference to opt out or to block
communication to certain web sites altogether. The discussions at
the workshop illustrated a lack of agreement about what type of
Cooper Informational [Page 4]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
tracking is acceptable, which technical mechanisms would be best
suited for different scenarios, and how the mechanisms would interact
with other aspects of privacy protection (such as notices to users).
The cross-site data-sharing discussion focused on current uses of
Open Authorization (OAuth) (with Facebook Connect, for example).
While improvements have been made in obtaining user consent to
sharing data between sites, challenges remain with regard to data
minimization, ease of use, hidden sharing of data, and centralization
of identity information.
2.2. SDO Discussion
Participants discussed past experiences in approaching privacy within
the IETF and the W3C. Individual protocol efforts within the IETF
have sought to address certain privacy threats over the years.
Protocol designers have taken steps to reduce the potential for
identifiability associated with protocol usage, such as in the IPv6
privacy extensions case [RFC4941]. Protocols architected to rely on
intermediaries have sought to minimize the user data exposed in
transit, most notably in SIP [RFC3323]. Protocol architectures used
in interpersonal exchange have sought to give users granular control
over their information, including presence [RFC2778] and geolocation
information [RFC3693]. Efforts to square privacy with usability are
ongoing; the ALTO working group [ALTO], for example, is working out
how to balance the needs of users and network operators to share data
with each other about content preferences and network topologies
against legitimate concerns about revealing too much of either kind
of information.
The IETF also has experience to draw on in building a culture of
security awareness. Beginning with [RFC1543], RFCs were required to
contain a Security Considerations section. But that simple mandate
did not immediately translate into the extensive security
consciousness that permeates the IETF today. Over many years and
with much effort invested, a more systematic approach to security has
evolved that makes use of a variety of tools and resources: the
security area itself, guidelines to RFC authors about security
considerations [RFC3552], the security directorate, security advisors
assigned to individual working groups, security tutorials at IETF
meetings, and so on.
The W3C likewise has a number of past efforts to draw on. One of the
earliest large-scale standards efforts aimed at improving web privacy
was the Platform for Privacy Preferences [P3P]. The idea behind P3P
was to have web sites provide machine-readable privacy policies that
browsers could vet and possibly override according to the user's
preference. The P3P policy expression language was robust enough to
Cooper Informational [Page 5]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
allow sites to make complex assertions about how they intended to
make use of data related to users, but market developments have
created a number of challenges with deployed policies.
More recent work at the W3C centered around the appropriateness of
various privacy features to be included in the Geolocation API
[Geolocation], which gives web sites a way to access the user's
precise location. The API requires that implementations obtain user
consent before accessing location information and allow users to
revoke that consent, but decisions about retention, secondary use,
and data minimization are left up to individual web sites and
applications. The geolocation effort and the P3P experience both
raise questions about how to navigate usability, regulation, business
incentives, and other aspects that normally lie outside the scope of
standards development organization (SDO) work.
3. Design Challenges
Workshop discussions surfaced a number of key issues that can make
designing privacy-sensitive protocols and systems difficult: the
increasing ease of user/device/application fingerprinting, unforeseen
information leakage, difficulties in distinguishing first parties
from third parties, complications arising from system dependencies,
and the lack of transparency and user awareness of privacy risks and
tradeoffs.
3.1. Ease of Fingerprinting
Internet applications and protocols now share so many unique
identifiers and other bits of information as part of their ordinary
operation that it is becoming increasingly easy for remote nodes to
create unique device or application fingerprints and re-identify the
same devices or applications over time [Panopticlick]. Hardware
identifiers, IP addresses, transport protocol parameters, cookies,
other forms of web storage, and a vast array of browser-based
information may be routinely shared as users browse the web. The
ease of fingerprinting presents a significant challenge for any
application that seeks to guarantee anonymity or unlinkability (such
as [Tor], which uses onion routing to strip out data that identifies
communications endpoints).
In many cases, the information that can be used to fingerprint a
device was not originally shared for that purpose; identifiers and
other information are provided to support some other functionality
(like IP addresses being shared in order to route packets), and may
incidentally be used to fingerprint. This complicates the task of
preventing fingerprinting, because each application or protocol
likely needs its own identifiers and information to function.
Cooper Informational [Page 6]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
Furthermore, some services are increasingly coming to rely on
fingerprinting in order to detect fraud or provide customized
content, for example. Finding privacy-friendly substitutes for
fingerprinting will only become more difficult as these services
become more entrenched (see Section 4.3).
The space of fingerprinting mitigations requires further exploration.
For example, workshop participants discussed the use of JavaScript
queries to obtain a browser's (often highly unique) font list, and
the tradeoffs associated with browsers instead (or additionally)
supporting some small subset of fonts in order to reduce browser
identifiability. As with many other privacy features, such a
restriction presents a tradeoff between privacy and usability, and in
the case of fingerprinting writ large, it may be difficult to find
consensus about which mitigations appropriately balance both values.
As a first step, the IETF may consider documenting the fingerprinting
implications for widely used IETF protocols (TCP, HTTP, SIP, etc.).
3.2. Information Leakage
Internet protocols and services tend to leak information in ways that
were not foreseen at design time, as explored during the IETF 77
technical plenary [IETF77] and in recent research [PrivLoss]
[PrivDiffus]. For example, the HTTP referrer header [RFC2616]
(misspelled in the original specification as "Referer") provides a
way for a web site to obtain the URI of the resource that referred
the user to the site. Referrer headers provide valuable insights to
web sites about where their users come from, but they can also leak
sensitive information (search terms or user IDs, for example),
because URI strings on the web often contain this information. The
infrastructure of an individual web site is often designed solely
with a view to making the site itself function properly, and
embedding search terms or other user-specific information in URIs may
serve that goal, but when those URIs leak out to other sites via a
referrer header, it creates the potential for third parties to use
and abuse the data contained therein.
The use of URIs for authentication of identity or capabilities can be
susceptible to the same kinds of problems. Relying on a "possession
model" where any user in possession of an authentication or
capability URI can gain access to a resource is only suitable in
situations with some means of control over URI distribution, and can
lead to wide leakage when used on the open web.
Cooper Informational [Page 7]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
3.3. Differentiating between First and Third Parties
Distinguishing between "first-party" interactions and "third-party"
interactions is important for understanding the implications of data
collection, sharing, and use that take place during the normal course
of web use. Unfortunately, the traditional meanings of these
concepts do not always clearly match up with user expectations or
evolving web technologies. Traditionally, the term "first party" has
been used to refer to the domain of a web site to which a user agent
directs an explicit request on behalf of a user. The term "third
party" has been used to refer to the domain of a web resource that a
user agent requests as a result of a first-party request, with the
third-party resource hosted at a different domain from the first-
party domain.
This distinction between first-party and third-party domains is in
part a result of long-standing user agent practices for handling HTTP
cookies. Typically, HTTP cookies are returned only to the origin
server that set them [RFC6265]. Cookies set from first-party domains
may not be read by third-party domains and vice versa. In some
cases, cookies set from first-party domains that contain subdomains
are accessible by all subdomains of the first-party domain. The
distinction between first-party domains and third-party domains is
reflected in browser-based cookie controls: major web browsers all
offer distinct first-party cookie settings and third-party cookie
settings.
However, a user's perception or expectation of the difference between
a "first party" and a "third party" may not fall neatly within these
distinctions. Users may expect that content hosted on a first-party
subdomain, but provided or used by a third party, would be treated as
third-party content, but browsers often treat it as first-party
content. Conversely, when third-party content appears from a source
with which the user has an established relationship -- such as the
Facebook "Like" button or other social widgets -- users may consider
their interaction with that content to be a desirable first-party
interaction, even though the content is hosted on a third-party
domain.
Handling these expectations programmatically is difficult, since the
same identifier structures (domains, subdomains) can correlate to
different user expectations in different contexts. On the other
hand, prompting users to express a preference about what kinds of
data collection and use should be allowable by each party encountered
on the web is not practical. Web and browser developers are actively
seeking novel ways to address this challenge, but there are few
clear-cut solutions.
Cooper Informational [Page 8]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
3.4. Lack of Transparency and User Awareness
There is no question that users lack a full understanding of how
their information is being used and what the tradeoffs are between
having their data collected and accessing services at little or no
cost. Much of the tracking that takes place on the web is passive
and invisible to users. Most companies disclose their data usage
practices in written privacy policies, but these policies are rarely
read, difficult to understand, and often fail to disclose salient
details (such as data retention lifetimes). Even when web tracking
is associated with some visual indication -- a highly targeted Gmail
ad or the Facebook "Like" button, for example -- users often do not
realize that it is occurring.
Efforts abound to attempt to present information about data
collection and usage in a more digestible way. P3P was one early
effort, but because it sought to support the expression of the vast
expanse of potential policies that companies may have, it developed
more complexity than the average user (or user interface) could
sustain. More recent efforts have focused on using a limited set of
icons to represent policies or provide an indication that tracking is
taking place.
4. Deployment and Analysis Challenges
Workshop participants identified a number of barriers to both
deployment of privacy-protecting technologies and the analysis of the
privacy properties of technological systems. These included the
difficulty of using generic protocols and tools to defend against
context-specific threats; the tension between privacy protection and
usability; and the difficulty of navigating between business, legal,
and individual incentives.
4.1. Generative Protocols vs. Contextual Threats
Privacy is not a binary state. Rather than operating either entirely
in private or entirely in public, individuals experience privacy
contextually, resulting in differing requirements for privacy
protection, depending on the circumstance and the individual. On the
Internet, the contextual nature of privacy means that threats against
it can vary, depending on the deployment scenario, the usage
scenario, the capabilities of different attackers, and the level of
concern that different kinds of attackers generate among different
users.
Cooper Informational [Page 9]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
Addressing the full waterfront of privacy threats within generic
protocols and tools is largely intractable. As a result, existing
privacy features developed at the network and application layers have
taken more targeted approaches. For example, privacy extensions for
stateless address autoconfiguration in IPv6 [RFC4941] support
addresses constructed dynamically rather than generating addresses
based on interface Media Access Control (MAC) addresses, which for
most users are persistent and unchangeable unique identifiers that
could be used for long-term tracking. While IPv6 privacy extensions
provide important protection against tracking and re-identification
by remote endpoints, they do not prevent -- and were not meant to
prevent -- all parties from being able to associate an IP address
with a particular user. ISPs and governments still have means to
make such associations, and remote endpoints have many other
mechanisms at their disposal to attempt to identify users
persistently, albeit without using IPv6 addresses.
This kind of experience with developing privacy tools shows that
designing privacy features into systems and protocols requires a
clear understanding of the scope of the threats they are designed to
address. This scope is currently being debated in discussion about
developing "Do Not Track" (DNT) mechanisms for the web and other
online contexts. A number of different approaches have been
proposed, including browser functionality to retain opt-out cookies,
an HTTP header that expresses the user's preference not to be
tracked, and a browser-based block list mechanism that prevents the
browser from communicating with tracking sites (for an overview, see
[OptOuts]). Regardless of the approach, these mechanisms function
based on some understanding of which "tracking" users should be able
to control, which in turn is based on some notion of the threats
presented by different kinds of tracking conducted by different kinds
of entities on the web. Should DNT mechanisms apply to sites with
which the user already has an established relationship? Or sites
that use only aggregate, non-individualized data? Does tracking for
fraud prevention or customization present different threats than
tracking for advertising or marketing purposes? The answers to these
questions will dictate DNT design choices.
The space of privacy threats on the Internet may appear particularly
broad from a protocol design perspective, because many of the
protocols in widest use are designed generically to support a variety
of applications and functionality. HTTP, for example, is used for a
wider variety of purposes than its original designers likely
anticipated; it is unsurprising that some of these purposes include
obtaining and using data about web users in ways that may be privacy-
infringing. It is unreasonable to ask protocol designers to mitigate
the potential privacy risks of every possible deployment that may
result from a particular protocol design; the key questions are about
Cooper Informational [Page 10]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
how the responsibility for protecting against privacy intrusion
should be split between protocols, APIs, applications, and services,
and which kinds of privacy features can best be implemented in each
place.
4.2. Tension between Privacy Protection and Usability
The workshop discussions highlighted the tension between providing
privacy protections and maintaining usability. Tor [Tor] provides
some salient examples of this tradeoff. Tor seeks to provide
protection against network surveillance, but by lengthening the
routing path, it may significantly increase round-trip time. Tor
obscures endpoint IP addresses; thus, it also interferes with
IP-based geolocation. Web browsing using Tor is particularly
challenging, as most browser plug-ins, much of JavaScript, and a
number of other browser-based features need to be blocked or
overridden in order to meet Tor's anonymity requirements. With Tor,
privacy clearly comes at a price.
Even less aggressive privacy features may come with usability
tradeoffs. One example is the blocking of HTTP referrer headers for
privacy protection reasons. Some sites provide a customized
experience to users based on the referring page, which means that
disabling referrer headers, as some browsers allow users to do, may
sacrifice user experience features on certain sites. Part of the
challenge is the level of nuance involved in making decisions about
privacy -- how can users be made to understand the privacy tradeoffs
of blocking HTTP referrer headers, for example, when the effects of
doing so will vary from site to site, or when there is limited UI
space to communicate the tradeoffs? Even seemingly simple privacy
controls like private browsing are not well understood.
The feature set that implementors choose to make available is often
reflective of the tension between usability and privacy. For
example, SIP [RFC3261] supports Secure/Multipurpose Internet Mail
Extensions (S/MIME) to secure SIP request bodies, but given its user
experience impact, few implementations include S/MIME support.
Although usability challenges are generally thought of as user-level
issues that are out of scope for the IETF, to the extent that they
trickle down into implementation decisions, they are highly relevant.
Although workshop participants reached few firm conclusions about how
to tackle usability issues arising from privacy features, the group
agreed that it may be beneficial for the W3C to do some more thinking
in this area, possibly toward the end of including usability
considerations in individual specifications. The challenge with such
an effort will be to provide useful guidance without being overly
prescriptive about how implementations should be designed.
Cooper Informational [Page 11]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
4.3. Interaction between Business, Legal, and Technical Incentives
4.3.1. Role of Regulation
The Internet has sustained commercial content for decades. Many
services are offered at little or no cost in exchange for being able
to sell advertising or collect user data (or both). As the
commercial value of the web in particular has exploded in recent
years, the paradigm for regulating privacy has also begun to change,
albeit more slowly.
At the dawn of the commercial Internet, few web sites had written
privacy policies that explained what they did with user data. Under
regulatory pressure, sites began to document their data collection
and usage practices in publicly posted policies. These policies
quickly became lengthy legal documents that commercial sites could
use to limit their liability, often by disclosing every possible
practice that the site might engage in, rather than informing users
about the salient practices of relevance to them.
Because so many businesses are fueled by user data, any move to give
users greater control over their data -- whether by better informing
them about its use or providing tools and settings -- often requires
the force of regulatory influence to succeed. In recent years,
regulatory authorities have put pressure on companies to improve
their privacy disclosures by making them simpler, more concise, more
prominent, and more accessible (see the 2010 Federal Trade Commission
privacy report [FTC]). Certain companies and industry sectors have
responded by developing privacy icons, using short notices in
addition to privacy policies, and making the language they use to
describe privacy practices more accessible and easier to understand.
Regulators play an important role in shaping incentive structures.
Companies often seek a balance between acting to limit their
liability and pushing the envelope with respect to uses of consumer
data. If regulators take a strong stand against certain practices --
as, for example, European legislators have against cookies being set
without user consent [Directive] -- legitimate businesses will feel
compelled to comply. But where there is regulatory uncertainty,
business responses may differ according to different market
strategies. The variety of potential responses to the emerging
discussion about mechanisms to control web tracking demonstrates this
variation: some businesses will embrace support for enhanced user
control, others may restrict their offerings or charge fees if they
are unable to track users, and still others may elect to circumvent
any new mechanisms put in place. The absence of regulatory pressure
tends to make the line between "good" and "bad" actors less evident.
Cooper Informational [Page 12]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
4.3.2. P3P: A Case Study of the Importance of Incentives
That absence of regulatory pressure revealed itself in the case of
P3P. The first version of P3P was standardized in the early 2000s,
when legalistic privacy policies were the norm and users had only
elementary controls over the data collected about them on the web.
P3P challenged that paradigm by providing a way for web sites to
express machine-readable privacy policies for browsers to vet and
possibly override according to the user's preference. The P3P policy
expression language was designed to allow sites to make complex
assertions about how they intended to make use of data related to
users.
The designers of Internet Explorer 6 made a crucial decision to only
allow sites to use third-party cookies if they had installed adequate
P3P policies. To avoid having their cookies blocked, most commercial
sites adopted some P3P policy, although many sites merely cut and
pasted from the example policies provided by the W3C. Today, large
numbers of sites are misrepresenting their privacy practices in their
P3P policies, but little has been done in response [Policies], and
browser support for P3P outside of IE is limited.
While theories abound to explain the current status of P3P
implementations, there is no doubt that the relationship between
regulatory and commercial incentives played a significant role. The
P3P policy expression language provided support for companies to be
able to express in granular detail how they handle user data, but the
companies had little reason to do so, preferring to protect
themselves from the liability associated with revealing potentially
unsavory practices. In theory, the threat of regulatory backlash
could have served as an incentive to publish accurate P3P policies,
but at the time of P3P's release, there was little regulatory
interest in moving beyond long, legalistic privacy policies. Even
today, regulators are reluctant to bring enforcement actions against
companies with misleading policies, perhaps because their own
incentive structure compels them to focus on other, more prominent
matters.
The P3P experience is instructive in general for attempts at crafting
privacy features that require the active participation of both ends
of a communication. Actors that are meant to articulate their own
privacy preferences, whether they be companies or individuals,
require incentives to do so, as do those that are meant to process
and react to such preferences. For example, the IETF's GEOPRIV
architecture allows for expression of user preferences about location
information [RFC4119]. While users may have more incentive to
disclose their privacy preferences than companies did in the P3P
case, successful use of the GEOPRIV model will require endpoints that
Cooper Informational [Page 13]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
consume location information to abide by those preferences, and in
certain contexts -- commercial or employment-related, for example --
they may be unwilling, or regulatory pressure may be required to spur
a change in practice.
It is clearly not the prerogative of Internet protocol developers to
seek to change existing incentive structures. But acknowledging what
motivates businesses, individuals, and regulators is crucial to
determining whether new privacy technologies will succeed or fail.
5. Conclusions and Next Steps
5.1. IETF Outlook
The workshop demonstrated that the understanding of how to address
privacy within the Internet standards community is nascent. The IETF
faces particular challenges, because IETF protocols generally do not
mandate implementation styles or pre-conceive particular deployment
contexts, making the space of potential privacy threats attributable
to any single protocol difficult to foresee at protocol design time.
Workshop participants nonetheless outlined a number of potential next
steps. Work has already begun to attempt to provide guidance to
protocol designers about the privacy impact of their specifications
[PrivCons]. In refining this guidance, many of the questions raised
at the workshop will need to be confronted, including those about how
to properly model privacy threats against generic protocols, how to
anticipate privacy risks that have been exposed in the previous
design efforts, and how to document risks that are more difficult to
foresee and mitigate. Workshop participants acknowledged that
developing such guidance is likely necessary if document authors are
expected to incorporate "Privacy Considerations" sections in their
documents, but even with guidance, this is likely to be an uphill
battle for many authors for some time to come.
As preliminary steps, those with privacy expertise may seek to apply
the current guidance to existing IETF protocols. The security area
directors have also created a privacy directorate where privacy
reviews of documents coming before the IESG are being conducted.
Participants also expressed an interest in further pursuing a number
of the technical topics discussed at the workshop, including lessons
learned from the experience of Tor and the fingerprinting
implications of HTTP, TCP, SIP, and other IETF protocols. These and
other efforts may be explored within the Internet Research Task Force
(IRTF) in addition to, or in lieu of, the IETF.
Cooper Informational [Page 14]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
5.2. W3C Outlook
The W3C is likewise in a position of seeking a more comprehensive
approach to privacy within the SDO. Because the work of the W3C
operates within a more defined scope than that of the IETF -- namely,
the web -- the questions before the W3C tend to lie more in the space
of distinguishing between what can appropriately be accomplished
within W3C specifications and what should be left to individual
implementations, a theme that repeated itself again and again at the
workshop.
To further develop its approach to privacy, the W3C will investigate
an interest group to discuss privacy topics. Some potential topics
that emerged from the workshop include the fingerprinting impact of
W3C protocols, data minimization in APIs, dealing with referrer
header privacy leakage, developing privacy considerations for
non-browser-based protocols, and developing usability considerations
as part of specification design.
5.3. Other Future Work
The workshop covered a number of topics that may deserve further
exploration in the IETF, the W3C, and the privacy community at large.
These include development of privacy terminology; articulation of
privacy threat models; analysis and experimentation with "Do Not
Track" mechanisms for the web; work on cross-site data sharing,
correlation, and linkability in web and non-web contexts; and
investigation of policy expression languages.
6. Acknowledgements
Thanks to Bernard Aboba, Nick Doty, and Hannes Tschofenig for their
early reviews.
7. Security Considerations
Workshop participants discussed security aspects related to privacy,
acknowledging that while much of the standards community may have
once viewed most relevant privacy concerns as being encompassed by
security considerations, there is a growing realization of privacy
threats that lie outside the security realm. These include concerns
related to data minimization, identifiability, and secondary use.
Earlier security work provided minimal provision for privacy
protection (e.g., the definition of "privacy" in [RFC2828] and some
guidance about private information in [RFC3552]).
Cooper Informational [Page 15]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
8. Informative References
[ALTO] IETF, "Application-Layer Traffic Optimization (alto)",
2011, <http://datatracker.ietf.org/wg/alto/charter/>.
[Directive]
European Parliament and Council of the European Union,
"Directive 2009/136/EC of the European Parliament and of
the Council", November 2009, <http://eur-lex.europa.eu/
LexUriServ/
LexUriServ.do?uri=OJ:L:2009:337:0011:01:EN:HTML>.
[FTC] Federal Trade Commission Staff, "A Preliminary FTC Staff
Report on Protecting Consumer Privacy in an Era of Rapid
Change: A Proposed Framework for Businesses and
Policymakers", December 2010,
<http://www.ftc.gov/opa/2010/12/privacyreport.shtm>.
[Geolocation]
Popescu, A., Ed., "Geolocation API Specification",
September 2010,
<http://www.w3.org/TR/2010/CR-geolocation-API-20100907/>.
[IETF77] Krishnamurthy, B., "Privacy Leakage on the Internet",
March 2010, <http://www.ietf.org/proceedings/77/slides/
plenaryt-5.pdf>.
[OptOuts] Cooper, A. and H. Tschofenig, "Overview of Universal
Opt-Out Mechanisms for Web Tracking", Work in Progress,
March 2011.
[P3P] Wenning, R., Ed., and M. Schunter, Ed., "The Platform for
Privacy Preferences 1.1 (P3P1.1) Specification",
November 2006, <http://www.w3.org/TR/P3P11/>.
[Panopticlick]
Electronic Frontier Foundation, "Panopticlick", 2011,
<http://panopticlick.eff.org/>.
[Policies] Leon, P., Cranor, L., McDonald, A., and R. McGuire, "Token
Attempt: The Misrepresentation of Website Privacy Policies
through the Misuse of P3P Compact Policy Tokens",
September 2010, <http://www.cylab.cmu.edu/research/
techreports/2010/tr_cylab10014.html>.
[PrivCons] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., and
J. Morris, "Privacy Considerations for Internet
Protocols", Work in Progress, October 2011.
Cooper Informational [Page 16]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
[PrivDiffus]
Krishnamurthy, B. and C. Wills, "Privacy Diffusion on the
Web: A Longitudinal Perspective", Proceedings of the World
Wide Web Conference, pages 541-550, Madrid, Spain,
April 2009, <http://www.cs.wpi.edu/~cew/papers/www09.pdf>.
[PrivLoss] Krishnamurthy, B., Malandrino, D., and C. Wills,
"Measuring Privacy Loss and the Impact of Privacy
Protection in Web Browsing", Proceedings of the Symposium
on Usable Privacy and Security, pages 52-63, Pittsburgh,
PA USA, ACM International Conference Proceedings Series,
July 2007,
<http://www.cs.wpi.edu/~cew/papers/soups07.pdf>.
[RFC1543] Postel, J., "Instructions to RFC Authors", RFC 1543,
October 1993.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2778] Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000.
[RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828,
May 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3323] Peterson, J., "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November 2002.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
J. Polk, "Geopriv Requirements", RFC 3693, February 2004.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
Cooper Informational [Page 17]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
[Tor] The Tor Project, Inc., "Tor", 2011,
<https://www.torproject.org/>.
[Workshop] IAB, W3C, ISOC, MIT CSAIL, "Internet Privacy Workshop
2010", 2011, <http://www.iab.org/activities/workshops/
internet-privacy-workshop-2010/>.
Cooper Informational [Page 18]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
Appendix A. Workshop Materials
Main page: http://www.iab.org/activities/workshops/
internet-privacy-workshop-2010/
Slides: http://www.iab.org/activities/workshops/
internet-privacy-workshop-2010/slides/
Minutes: http://www.iab.org/activities/workshops/
internet-privacy-workshop-2010/minutes/
Position papers: http://www.iab.org/activities/workshops/
internet-privacy-workshop-2010/papers/
Appendix B. Workshop Participants
o Fu-Ming Shih, MIT
o Ian Jacobi, MIT
o Steve Woodrow, MIT
o Nick Mathewson, The Tor Project
o Peter Eckersley, Electronic Frontier Foundation
o John Klensin, IAB
o Oliver Hanka, Technical University Munich
o Alan Mislove, Northeastern University
o Ashkan Soltani, FTC
o Sam Hartman, Painless Security
o Kevin Trilli, TRUSTe
o Dorothy Gellert, InterDigital
o Aaron Falk, Raytheon - BBN Technologies
o Sean Turner, IECA
o Wei-Yeh Lee, NAVTEQ
o Chad McClung, The Boeing Company
o Jan Seedorf, NEC
o Dave Crocker, Brandenburg InternetWorking
o Lorrie Cranor, Carnegie Mellon University
o Noah Mendelsohn, W3C TAG Chair
o Stefan Winter, RESTENA
o Craig Wittenberg, Microsoft
o Bernard Aboba, IAB/Microsoft
o Heather West, Google
o Blaine Cook, British Telecom
o Kasey Chappelle, Vodafone Group
o Russ Housley, IETF Chair/Vigil Security, LLC
o Daniel Appelquist, Vodafone R&D
o Olaf Kolkman, IAB Chair
o Jon Peterson, IAB/NeuStar, Inc.
o Balachander Krishnamurthy, AT&T Labs--Research
o Marc Linsner, Cisco Systems
Cooper Informational [Page 19]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
o Jorge Cuellar, Siemens AG
o Arvind Narayanan, Stanford University
o Eric Rescorla, Skype
o Cullen Jennings, Cisco
o Christine Runnegar, Internet Society
o Alissa Cooper, Center for Democracy & Technology
o Jim Fenton, Cisco
o Oshani Seneviratne, MIT
o Lalana Kagal, MIT
o Fred Carter, Information & Privacy Commissioner of Ontario, Canada
o Frederick Hirsch, Nokia
o Benjamin Heitmann, DERI, NUI Galway, Ireland
o John Linn, RSA, The Security Division of EMC
o Paul Trevithick, Azigo
o Ari Schwartz, National Institute of Standards and Technology
o David Evans, University of Cambridge
o Nick Doty, UC Berkeley, School of Information
o Sharon Paradesi, MIT
o Jonathan Mayer, Stanford University
o David Maher, Intertrust
o Brett McDowell, PayPal
o Leucio Antonio Cutillo, Eurecom
o Susan Landau, Radcliffe Institute for Advanced Study, Harvard
University
o Christopher Soghoian, FTC In-house Technologist, Center for
Applied Cybersecurity Research, Indiana University
o Trent Adams, Internet Society
o Thomas Roessler, W3C
o Karen O'Donoghue, ISOC
o Hannes Tschofenig, IAB/Nokia Siemens Networks
o Lucy Elizabeth Lynch, Internet Society
o Karen Sollins, MIT
o Tim Berners-Lee, W3C
Cooper Informational [Page 20]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
Appendix C. Accepted Position Papers
1. "Addressing the privacy management crisis in online social
networks" by Krishna Gummadi, Balachander Krishnamurthy, and
Alan Mislove
2. "Thoughts on Adding "Privacy Considerations" to Internet Drafts"
by Alissa Cooper and John Morris
3. "Toward Objective Global Privacy Standards" by Ari Schwartz
4. "SocialKeys: Transparent Cryptography via Key Distribution over
Social Networks" by Arvind Narayanan
5. "Web Crawlers and Privacy: The Need to Reboot Robots.txt" by
Arvind Narayanan and Pete Warden
6. "I Know What You Will Do Next Summer" by Balachander
Krishnamurthy
7. "An architecture for privacy-enabled user profile portability on
the Web of Data" by Benjamin Heitmann and Conor Hayes
8. "Addressing Identity on the Web" by Blaine Cook
9. "Protection-by-Design: Enhancing ecosystem capabilities to
protect personal information" by Jonathan Fox and Brett McDowell
10. "Privacy-preserving identities for a safer, more trusted
internet" by Christian Paquin
11. "Why Private Browsing Modes Do Not Deliver Real Privacy" by
Christopher Soghoian
12. "Incentives for Privacy" by Cullen Jennings
13. "Joint Privacy Workshop: Position Comments by D. Crocker" by
Dave Crocker
14. "Using properties of physical phenomena and information flow
control to manage privacy" by David Evans and David M. Eyers
15. "Privacy Approaches for Internet Video Advertising" by Dave
Maher
16. "Privacy on the Internet" by Dorothy Gellert
Cooper Informational [Page 21]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
17. "Can We Have a Usable Internet Without User Trackability?" by
Eric Rescorla
18. "Privacy by Design: The 7 Foundational Principles --
Implementation and Mapping of Fair Information Practices" by
Fred Carter and Ann Cavoukian
19. "Internet Privacy Workshop Position Paper: Privacy and Device
APIs" by Frederick Hirsch
20. "Position Paper for Internet Privacy Workshop" by Heather West
21. "I 'like' you, but I hate your apps" by Ian Glazer
22. "Privicons: A approach to communicating privacy preferences
between Users" by E. Forrest and J. Schallabock
23. "Privacy Preservation Techniques to establish Trustworthiness
for Distributed, Inter-Provider Monitoring" by J. Seedorf, S.
Niccolini, A. Sarma, B. Trammell, and G. Bianchi
24. "Trusted Intermediaries as Privacy Agents" by Jim Fenton
25. "Protocols are for sharing" by John Kemp
26. "On Technology and Internet Privacy" by John Linn
27. "Do Not Track: Universal Web Tracking Opt-out" by Jonathan Mayer
and Arvind Narayanan
28. "Location Privacy Protection Through Obfuscation" by Jorge
Cuellar
29. "Everything we thought we knew about privacy is wrong" by Kasey
Chappelle and Dan Appelquist
30. "TRUSTe Position Paper" by Kevin Trilli
31. "Position Paper: Incentives for Adoption of Machine-Readable
Privacy Notices" by Lorrie Cranor
32. "Facilitate, don't mandate" by Ari Rabkin, Nick Doty, and
Deirdre K. Mulligan
33. "Location Privacy in Next Generation Internet Architectures" by
Oliver Hanka
34. "HTTPa: Accountable HTTP" by Oshani Seneviratne and Lalana Kagal
Cooper Informational [Page 22]
RFC 6462 2010 IAB-W3C-ISOC-MIT Privacy Workshop January 2012
35. "Personal Data Service" by Paul Trevithick
36. "Several Pressing Problems in Hypertext Privacy" by Peter
Eckersley
37. "Adding Privacy in Existing Security Systems" by Sam Hartman
38. "Mobility and Privacy" by S. Brim, M. Linsner, B. McLaughlin,
and K. Wierenga
39. "Saveface: Save George's faces in Social Networks where Contexts
Collapse" by Fuming Shih and Sharon Paradesi
40. "eduroam -- a world-wide network access roaming consortium on
the edge of preserving privacy vs. identifying users" by Stefan
Winter
41. "Effective Device API Privacy: Protecting Everyone (Not Just the
User)" by Susan Landau
42. "Safebook: Privacy Preserving Online Social Network" by L.
Antonio Cutillo, R. Molva, and M. Onen
Author's Address
Alissa Cooper
CDT
1634 I Street NW, Suite 1100
Washington, DC 20006
USA
EMail: acooper@cdt.org
URI: http://www.cdt.org/
Cooper Informational [Page 23]