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.

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.

   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

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.

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

   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

   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.

   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.

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.

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.

   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

   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.

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.

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

   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.

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]).

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.

   [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.

   [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/>.

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

   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

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

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

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/