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Versions: (draft-morris-privacy-considerations) 00 01 02 03 04 05 06 07 08 09 RFC 6973

Network Working Group                                          A. Cooper
Internet-Draft                                                       CDT
Intended status: Informational                             H. Tschofenig
Expires: September 13, 2012                       Nokia Siemens Networks
                                                                B. Aboba
                                                   Microsoft Corporation
                                                             J. Peterson
                                                           NeuStar, Inc.
                                                               J. Morris
                                                          March 12, 2012


             Privacy Considerations for Internet Protocols
                draft-iab-privacy-considerations-02.txt

Abstract

   This document offers guidance for developing privacy considerations
   for IETF documents and aims to make protocol designers aware of
   privacy-related design choices.

   Discussion of this document is taking place on the IETF Privacy
   Discussion mailing list (see
   https://www.ietf.org/mailman/listinfo/ietf-privacy).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 13, 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



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   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.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Internet Privacy Threat Model  . . . . . . . . . . . . . . . .  5
     3.1.  Communications Model . . . . . . . . . . . . . . . . . . .  5
     3.2.  Privacy Threats  . . . . . . . . . . . . . . . . . . . . .  6
       3.2.1.  Combined Security-Privacy Threats  . . . . . . . . . .  6
       3.2.2.  Privacy-Specific Threats . . . . . . . . . . . . . . .  8
   4.  Internet Privacy Goals . . . . . . . . . . . . . . . . . . . . 11
     4.1.  Data Minimization  . . . . . . . . . . . . . . . . . . . . 11
     4.2.  User Participation . . . . . . . . . . . . . . . . . . . . 12
     4.3.  Accountability . . . . . . . . . . . . . . . . . . . . . . 12
     4.4.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 12
   5.  Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.1.  General  . . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.2.  Data Minimization  . . . . . . . . . . . . . . . . . . . . 13
     5.3.  User Participation . . . . . . . . . . . . . . . . . . . . 14
     5.4.  Accountability . . . . . . . . . . . . . . . . . . . . . . 15
     5.5.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 15
   6.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   7.  Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 23
     11.2. Informative References . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25












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1.  Introduction

   [RFC3552] provides detailed guidance to protocol designers about both
   how to consider security as part of protocol design and how to inform
   readers of IETF documents about security issues.  This document
   intends to provide a similar set of guidance for considering privacy
   in protocol design.

   Whether any individual document will require a specific privacy
   considerations section will depend on the document's content.
   Documents whose entire focus is privacy may not merit a separate
   section (for example, [RFC3325]).  For certain specifications,
   privacy considerations are a subset of security considerations and
   can be discussed explicitly in the security considerations section.
   The guidance provided here can and should be used to assess the
   privacy considerations of protocol, architectural, and operational
   specifications and to decide whether those considerations are to be
   documented in a stand-alone section, within the security
   considerations section, or throughout the document.

   Privacy is a complicated concept with a rich history that spans many
   disciplines.  Many sets of privacy principles and privacy design
   frameworks have been developed in different forums over the years.
   These include the Fair Information Practices (FIPs), a baseline set
   of privacy protections pertaining to the collection and use of data
   about individuals (see [OECD] for one example), and the Privacy by
   Design concept, which provides high-level privacy guidance for
   systems design (see [PbD] for one example).  The guidance provided in
   this document is inspired by this prior work, but it aims to be more
   concrete, pointing protocol designers to specific engineering choices
   that can impact the privacy of the individuals that make use of
   Internet protocols.

   Privacy as a legal concept is understood differently in different
   jurisdictions.  The guidance provided in this document is generic and
   can be used to inform the design of any protocol to be used anywhere
   in the world, without reference to specific legal frameworks.

   This document is organized as follows.  Section 2 describes the
   extent to which the guidance offered is applicable within the IETF.
   Section 3 discusses threats to privacy as they apply to Internet
   protocols.  Section 4 outlines privacy goals.  Section 5 provides the
   guidelines for analyzing and documenting privacy considerations
   within IETF specifications.  Section 6 examines the privacy
   characteristics of an IETF protocol to demonstrate the use of the
   guidance framework.  Section 7 provides a concise glossary of terms
   used in this document, with a more complete discussion of some of the
   terms available in [I-D.iab-privacy-terminology].



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2.  Scope

   The core function of IETF activity is building protocols.  Internet
   protocols are often built flexibly, making them useful in a variety
   of architectures, contexts, and deployment scenarios without
   requiring significant interdependency between disparately designed
   components.  Although some protocols assume particular architectures
   at design time, it is not uncommon for architectural frameworks to
   develop later, after implementations exist and have been deployed in
   combination with other protocols or components to form complete
   systems.

   As a consequence, the extent to which protocol designers can foresee
   all of the privacy implications of a particular protocol at design
   time is significantly limited.  An individual protocol may be
   relatively benign on its own, but when deployed within a larger
   system or used in a way not envisioned at design time, its use may
   create new privacy risks.  The guidelines in Section 5 ask protocol
   designers to consider how their protocols are expected to interact
   with systems and information that exist outside the protocol bounds,
   but not to imagine every possible deployment scenario.

   Furthermore, in many cases the privacy properties of a system are
   dependent upon API specifics, internal application functionality,
   database structure, local policy, and other details that are specific
   to particular instantiations and generally outside the scope of the
   work conducted in the IETF.  The guidance provided here may be useful
   in making choices about those details, but its primary aim is to
   assist with the design, implementation, and operation of protocols.
   Privacy issues, even those related to protocol development, go beyond
   the technical guidance discussed herein.

   As an example, consider HTTP [RFC2616], which was designed to allow
   the exchange of arbitrary data.  A complete analysis of the privacy
   considerations for uses of HTTP might include what type of data is
   exchanged, how this data is stored, and how it is processed.  Hence
   the analysis for an individual's static personal web page would be
   different than the use of HTTP for exchanging health records.  A
   protocol designer working on HTTP extensions (such as WebDAV
   [RFC4918]) is not expected to describe the privacy risks derived from
   all possible usage scenarios, but rather the privacy properties
   specific to the extensions and any particular uses of the extensions
   that are expected and foreseen at design time.








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3.  Internet Privacy Threat Model

   Privacy harms come in a number of forms, including harms to financial
   standing, reputation, solitude, autonomy, and safety.  A victim of
   identity theft or blackmail, for example, may suffer a financial loss
   as a result.  Reputational harm can occur when disclosure of
   information about an individual, whether true or false, subjects that
   individual to stigma, embarrassment, or loss of personal dignity.
   Intrusion or interruption of an individual's life or activities can
   harm the individual's ability to be left alone.  When individuals or
   their activities are monitored, exposed, or at risk of exposure,
   those individuals may be stifled from expressing themselves,
   associating with others, and generally conducting their lives freely.
   In cases where such monitoring is for the purpose of stalking or
   violence, it can put individuals in physical danger.

   This section lists common privacy threats (drawing liberally from
   [Solove]), showing how each of them may cause individuals to incur
   privacy harms and providing examples of how these threats can exist
   on the Internet.

3.1.  Communications Model

   To understand attacks in the privacy-harm sense, it is helpful to
   consider the overall communication architecture and different actors'
   roles within it.  Consider a protocol element that initiates
   communication with some recipient (an "initiator").  Privacy analysis
   is most relevant for protocols with use cases in which the initiator
   acts on behalf of a natural person (or different people at different
   times).  It is this natural person -- the data subject -- whose
   privacy is potentially threatened.

   Communications may be direct between the initiator and the recipient,
   or they may involve an intermediary (such as a proxy or cache) that
   is necessary for the two parties to communicate.  In some cases this
   intermediary stays in the communication path for the entire duration
   of the communication and sometimes it is only used for communication
   establishment, for either inbound or outbound communication.  In rare
   cases there may be a series of intermediaries that are traversed.

   Some communications tasks require multiple protocol interactions with
   different entities.  For example, a request to an HTTP server may be
   preceded by an interaction between the initiator and an
   Authentication, Authorization, and Accounting (AAA) server or DNS
   resolver.  In this case, the HTTP server is the recipient and the
   other entities are enablers of the initiator-to-recipient
   communication.  Similarly, a single communication with the recipient
   my generate further protocol interactions between either the



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   initiator or the recipient and other entities.  For example, an HTTP
   request might trigger interactions with an authentication server or
   with other resource servers.

   As a general matter, recipients, intermediaries, and enablers are
   usually assumed to be authorized to receive and handle data from
   initiators.  As [RFC3552] explains, "we assume that the end-systems
   engaging in a protocol exchange have not themselves been
   compromised."

   Although they may not generally be considered as attackers,
   recipients, intermediaires, and enablers may all pose privacy threats
   (depending on the context) because they are able to observe and
   collect privacy-relevant data.  These entities are collectively
   described below as "observers" to distinguish them from traditional
   attackers.  From a privacy perspective, one important type of
   attacker is an eavesdropper: an entity that passively observes the
   initiator's communications without the initiator's knowledge or
   authorization.

   The threat descriptions in the next section explain how observers and
   attackers might act to harm data subjects' privacy.  Different kinds
   of attacks may be feasible at different points in the communications
   path.  For example, an observer could mount surveillance or
   identification attacks between the initiator and intermediary, or
   instead could surveil an enabler (e.g., by observing DNS queries from
   the initiator).

3.2.  Privacy Threats

   Some privacy threats are already considered in IETF protocols as a
   matter of routine security analysis.  Others are more pure privacy
   threats that existing security considerations do not usually address.
   The threats described here are divided into those that may also be
   considered security threats and those that are primarily privacy
   threats.

   Note that an individual's knowledge and authorization of the
   practices described below can greatly affect the extent to which they
   threaten privacy.  If a data subject authorizes surveillance of his
   own activities, for example, the harms associated with it may be
   significantly mitigated.

3.2.1.  Combined Security-Privacy Threats







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3.2.1.1.  Surveillance

   Surveillance is the observation or monitoring of an individual's
   communications or activities.  The effects of surveillance on the
   individual can range from anxiety and discomfort to behavioral
   changes such as inhibition and self-censorship to the perpetration of
   violence against the individual.  The individual need not be aware of
   the surveillance for it to impact privacy -- the possibility of
   surveillance may be enough to harm individual autonomy.

   Surveillance can be conducted by observers or eavesdroppers at any
   point along the communications path.  Confidentiality protections (as
   discussed in [RFC3552] Section 3) are necessary to prevent
   surveillance of the content of communications.  To prevent traffic
   analysis or other surveillance of communications patterns, other
   measures may be necessary, such as [Tor].

3.2.1.2.  Stored Data Compromise

   End systems that do not take adequate measures to secure stored data
   from unauthorized or inappropriate access expose individuals to
   potential financial, reputational, or physical harm.

   By and large, protecting against stored data compromise is outside
   the scope of IETF protocols.  However, a number of common protocol
   functions -- key management, access control, or operational logging,
   for example -- require the storage of data about initiators of
   communications.  When requiring or recommending that information
   about initiators or their communications be stored or logged by end
   systems (see, e.g., RFC 6302), it is important to recognize the
   potential for that information to be compromised and for that
   potential to be weighed against the benefits of data storage.  Any
   recipient, intermediary, or enabler that stores data may be
   vulnerable to compromise.

3.2.1.3.  Intrusion

   Intrusion consists of invasive acts that disturb or interrupt one's
   life or activities.  Intrusion can thwart individuals' desires to be
   let alone, sap their time or attention, or interrupt their
   activities.

   Unsolicited mail and denial-of-service attacks are the most common
   types of intrusion on the Internet.  Intrusion can be perpetrated by
   any attacker that is capable of sending unwanted traffic to the
   initiator.





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3.2.2.  Privacy-Specific Threats

3.2.2.1.  Correlation

   Correlation is the combination of various pieces of information about
   an individual.  Correlation can defy people's expectations of the
   limits of what others know about them.  It can increase the power
   that those doing the correlating have over individuals as well as
   correlators' ability to pass judgment, threatening individual
   autonomy and reputation.

   Correlation is closely related to identification.  Internet protocols
   can facilitate correlation by allowing data subjects' activities to
   be tracked and combined over time.  The use of persistent or
   infrequently refreshed identifiers at any layer of the stack can
   facilitate correlation.  For example, an initiator's persistent use
   of the same device ID, certificate, or email address across multiple
   interactions could allow recipients to correlate all of the
   initiator's communications over time.

   In theory any observer or attacker that receives an initiator's
   communications can engage in correlation.  The extent of the
   potential for correlation will depend on what data the entity
   receives from the initiator and has access to otherwise.  Often,
   intermediaries only require a small amount of information for message
   routing and/or security.  In theory, protocol mechanisms could ensure
   that end-to-end information is not made accessible to these entities,
   but in practice the difficulty of deploying end-to-end security
   procedures, additional messaging or computational overhead, and other
   business or legal requirements often slow or prevent the deployment
   of end-to-end security mechanisms, giving intermediaries greater
   exposure to initiators' data than is strictly necessary.

3.2.2.2.  Identification

   Identification is the linking of information to a particular
   individual.  In some contexts it is perfectly legitimate to identify
   individuals, whereas in others identification may potentially stifle
   individuals' activities or expression by inhibiting their ability to
   be anonymous or pseudonymous.  Identification also makes it easier
   for individuals to be explicitly controlled by others (e.g.,
   governments).

   Many protocol identifiers, such as those used in SIP or XMPP, may
   allow for the direct identification of data subjects.  Protocol
   identifiers may also contribute indirectly to identification via
   correlation.  For example, a web site that does not directly
   authenticate users may be able to match its HTTP header logs with



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   logs from another site that does authenticate users, rendering users
   on the first site identifiable.

   As with correlation, any observer or attacker may be able to engage
   in identification depending on the information about the initiator
   that is available via the protocol mechanism or other channels.

3.2.2.3.  Secondary Use

   Secondary use is the use of collected information without the data
   subject's consent for a purpose different from that for which the
   information was collected.  Secondary use may violate people's
   expectations or desires.  The potential for secondary use can
   generate uncertainty over how one's information will be used in the
   future, potentially discouraging information exchange in the first
   place.

   One example of secondary use would be a network access server that
   uses an initiator's access requests to track the initiator's
   location.  Any observer or attacker could potentially make unwanted
   secondary uses of initiators' data.

3.2.2.4.  Disclosure

   Disclosure is the revelation of truthful information about a person
   that affects the way others judge the person.  Disclosure can violate
   people's expectations of the confidentiality of the data they share.
   The threat of disclosure may deter people from engaging in certain
   activities for fear of reputational harm.

   Any observer or attacker that receives data about an initiator may
   choose to engage in disclosure.  In most cases, there is nothing done
   at the protocol level to influence or limit disclosure, although
   there are some exceptions.  For example, the GEOPRIV architecture
   [RFC6280] provides a way for users to express a preference that their
   location information not be disclosed beyond the intended recipient.

3.2.2.5.  Exclusion

   Exclusion is the failure to allow the data subject to know about the
   data that others have about him or her and to participate in its
   handling and use.  Exclusion reduces accountability on the part of
   entities that maintain information about people and creates a sense
   of vulnerability about individuals' ability to control how
   information about them is collected and used.

   The most common way for Internet protocols to be involved in limiting
   exclusion is through access control mechanisms.  The presence



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   architecture developed in the IETF is a good example where data
   subjects are included in the control of information about them.
   Using a rules expression language (e.g., Presence Authorization Rules
   [RFC5025]), presence clients can authorize the specific conditions
   under which their presence information may be shared.

   Exclusion is primarily considered problematic when the recipient
   fails to involve the initiator in decisions about data collection,
   handling, and use.  Eavesdroppers engage in exclusion by their very
   nature since their data collection and handling practices are covert.









































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4.  Internet Privacy Goals

   Privacy is notoriously difficult to measure and quantify.  The extent
   to which a particular protocol, system, or architecture "protects" or
   "enhances" privacy is dependent on a large number of factors relating
   to its design, use, and potential misuse.  However, there are certain
   widely recognized privacy properties against which designs may be
   assessed for their potential to impact privacy.  This section adapts
   these properties into four privacy goals for Internet protocols: (1)
   data minimization, (2) user participation, (3) accountability, and
   (4) security.

4.1.  Data Minimization

   Data minimization refers to collecting, using, and storing the
   minimal data necessary to perform a task.  The less data about data
   subjects that gets exchanged in the first place, the lower the
   chances of that data being used for privacy invasion.

   Data minimization is comprised of a number of mutually exclusive sub-
   goals:

   o  Use limitation: Limiting the uses to which data is put helps
      contain the spread of data to third parties and protects against
      uses that may violate data subjects' expectations.

   o  Retention limitation: Limiting the duration of data storage
      reduces the risk of stored data compromise.

   o  Identifiability limitation: Minimization pertains not only to the
      amount of data exchanged, but also the extent to which it can be
      used to identify data subjects.  Reducing the identifiability of
      data by using pseudonymous or anonymous identifiers helps to
      weaken the link between a data subject and his or her
      communications.  Refreshing or recycling identifiers reduces the
      possibility that multiple protocol interactions or communications
      can be correlated back to the same data subject.

   o  Sensitivity limitation: The sensitivity of data is another
      property that can be minimized.  For example, the street address
      of a building that an individual visits may be considered to be a
      more sensitive piece of information than the city and postal code
      in which the building is located.  Collecting, using, and storing
      less sensitive data may mitigate the damage caused by secondary
      use, disclosure, stored data compromise, and correlation.






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4.2.  User Participation

   As explained in Section 3.2.2.5, data collection and use that happens
   "in secret," without the data subject's knowledge, is apt to violate
   the subject's expectation of privacy and may create incentives for
   misuse of data.  As a result, privacy regimes tend to include
   provisions to support informing data subjects about data collection
   and use and involving them in decisions about the treatment of their
   data.  In an engineering context, supporting the goal of user
   participation usually means providing ways for users to control the
   data that is shared about them.

4.3.  Accountability

   An entity that collects, uses, or stores data can undergird its
   commitments to the other privacy goals by providing mechanisms by
   which data subjects and third parties can hold the entity accountable
   for those commitments.  These mechanisms usually allow for
   verification of what data is collected or stored and with whom it is
   shared, again helping to mitigate the threat of exclusion.

4.4.  Security

   Keeping data secure at rest and in transit is another important
   component of privacy protection.  As they are described in [RFC3552]
   Section 2, a number of security goals also serve to enhance privacy:

   o  Confidentiality: Keeping data secret from unintended listeners.

   o  Peer entity authentication: Ensuring that the endpoint of a
      communication is the one that is intended (in support of
      maintaining confidentiality).

   o  Unauthorized usage: Limiting data access to only those users who
      are authorized, helping to prevent stored data compromise.

   o  Inappropriate usage: Limiting how authorized users can use data.
      (Note that this goal also falls within data minimization.)













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5.  Guidelines

   This section provides guidance for document authors in the form of a
   questionnaire about a protocol being designed.  The questionnaire may
   be useful at any point in the design process, particularly after
   document authors have developed a high-level protocol model as
   described in [RFC4101].

   Note that the guidance does not recommend specific practices.  The
   range of protocols developed in the IETF is too broad to make
   recommendations about particular uses of data or how privacy might be
   balanced against other design goals.  However, by carefully
   considering the answers to each question, document authors should be
   able to produce a comprehensive analysis that can serve as the basis
   for discussion of whether the protocol adequately protects against
   privacy threats.

   The framework is divided into four sections that address each of the
   goals from Section 4, plus a general section.  Security is not fully
   elaborated since substantial guidance already exists in [RFC3552].

5.1.  General

      a.  Trade-offs.  Does the protocol make trade-offs between privacy
      and usability, privacy and efficiency, privacy and
      implementability, or privacy and other design goals?  Describe the
      trade-offs and the rationale for the design chosen.

5.2.  Data Minimization

      a.  Identifiers.  What identifiers does the protocol use for
      distinguishing initiators of communications?  Does the protocol
      use identifiers that allow different protocol interactions to be
      correlated?

      b.  Personal data.  What information does the protocol expose
      about data subjects and/or their devices (other than the
      identifiers discussed in (a))?  To what extent is this information
      linked to the identities of data subjects?  How does the protocol
      combine personal data with the identifiers discussed in (a)?

      c.  Observers.  Which information discussed in (a) and (b) is
      exposed to each other protocol entity (i.e., recipients,
      intermediaries, and enablers)?  Are there ways for protocol
      implementers to choose to limit the information shared with each
      entity?  Are there operational controls available to limit the
      information shared with each entity?




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      d.  Fingerprinting.  In many cases the specific ordering and/or
      occurrences of information elements in a protocol allow users,
      devices, or software using the protocol to be fingerprinted.  Is
      this protocol vulnerable to fingerprinting?  If so, how?

      e.  Persistence of identifiers.  What assumptions are made in the
      protocol design about the lifetime of the identifiers discussed in
      (a)?  Does the protocol allow implementers or users to delete or
      recycle identifiers?  How often does the specification recommend
      to delete or recycle identifiers by default?

      f.  Correlation.  Are there expected ways that information exposed
      by the protocol will be combined or correlated with information
      obtained outside the protocol?  How will such combination or
      correlation facilitate fingerprinting of a user, device, or
      application?  Are there expected combinations or correlations with
      outside data that will make users of the protocol more
      identifiable?

      g.  Retention.  Do the protocol or its anticipated uses require
      that the information discussed in (a) or (b) be retained by
      recipients, intermediaries, or enablers?  Is the retention
      expected to be persistent or temporary?

5.3.  User Participation

      a.  User control.  What controls or consent mechanisms does the
      protocol define or require before personal data or identifiers are
      shared or exposed via the protocol?  If no such mechanisms are
      specified, is it expected that control and consent will be handled
      outside of the protocol?

      b.  Control over sharing with individual recipients.  Does the
      protocol provide ways for initiators to share different
      information with different recipients?  If not, are there
      mechanisms that exist outside of the protocol to provide
      initiators with such control?

      c.  Control over sharing with intermediaries.  Does the protocol
      provide ways for initiators to limit which information is shared
      with intermediaries?  If not, are there mechanisms that exist
      outside of the protocol to provide users with such control?  Is it
      expected that users will have relationships (contractual or
      otherwise) with intermediaries that govern the use of the
      information?






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      d.  Preference expression.  Does the protocol provide ways for
      initiators to express data subjects' preferences to recipients or
      intermediaries with regard to the use or disclosure of their
      personal data?

5.4.  Accountability

      a.  Verification.  If the protocol provides for user preference
      expression, does it also define or require mechanisms that allow
      initiators to verify that data subjects' preferences are being
      honored?  If not, are there mechanisms that exist outside of the
      protocol that allow for verification?

5.5.  Security

      a.  Surveillance.  How do the protocol's security considerations
      prevent surveillance, including eavesdropping and traffic analyis?

      b.  Stored data compromise.  How do the protocol's security
      considerations prevent or mitigate stored data compromise?

      c.  Intrusion.  How do the protocol's security considerations
      prevent or mitigate intrusion, including denial-of-service attacks
      and unsolicited communications more generally?



























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6.  Example

   [To be provided in a future version once the guidance is settled.]
















































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7.  Glossary

   $ Anonymity

      The state of being anonymous.  See [I-D.iab-privacy-terminology].

   $ Anonymous

      A property of a data subject in which an observer or attacker
      cannot identify the data subject within a set of other subjects
      (the anonymity set).

   $ Attacker

      An entity that intentionally works against some protection goal.

   $ Attribute

      A property of a data subject or initiator.

   $ Correlation

      The combination of various pieces of information about a data
      subject.

   $ Data Subject

      An identified natural person or a natural person who can be
      identified, directly or indirectly.

   $ Eavesdropper

      An entity that passively observes an initiator's communications
      without the initiator's knowledge or authorization.  See
      [RFC4949].

   $ Enabler

      A protocol entity that facilitates communication between an
      initiator and a recipient without being directly in the
      communications path.

   $ Fingerprint

      A set of information elements that identifies a device,
      application, or initiator.





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   $ Fingerprinting

      The process of an observer or attacker partially or fully
      identifying a device, application, or initiator based on multiple
      information elements communicated to the observer or attacker.
      See [EFF].

   $ Identifiable

      A state in which a data subject's identity is known.

   $ Identifiability

      The extent to which a data subject is identifiable.  See
      [I-D.iab-privacy-terminology].

   $ Identifier

      A data object that represents a specific identity of a protocol
      entity or data subject.  See [RFC4949].

   $ Identification

      The linking of information to a particular data subject to infer
      the subject's identity.

   $ Identity

      Any subset of a data subject's attributes that identifies the
      subject within a given context.  Data subjects usually have
      multiple identities for use in different contexts.

   $ Initiator

      A protocol entity that initiates communications with a recipient.

   $ Intermediary

      A protocol entity that sits between the initiator and the
      recipient and is necessary for the initiator and recipient to
      communicate.

   $ Item of Interest (IOI)

      Any data item that an observer or attacker might be interested in.
      This includes attributes, identifiers, identities, communications,
      or actions (such as the sending or receiving of a communication).
      See [I-D.iab-privacy-terminology].



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   $ Observer

      An entity that is authorized to receive and handle data from an
      initiator and thereby is able to observe and collect information,
      potentially posing privacy threats depending on the context.
      Recipients, intermediaries, and enablers can all be observers.

   $ Personal Data

      Any information relating to a data subject.

   $ (Protocol) Interaction

      A unit of communication within a particular protocol.  A single
      interaction may be compromised of a single message between an
      initiator and recipient or multiple messages, depending on the
      protocol.

   $ Pseudonym

      An identifier of a data subject other than the subject's real
      name.

   $ Pseudonymity

      The state of being pseudonymous.  See
      [I-D.iab-privacy-terminology].

   $ Pseudonymous

      A property of a data subject in which the subject is identified by
      a pseudonym.

   $ Recipient

      A protocol entity that recieves communications from an initiator.

   $ Traffic Analysis

      The inference of information from observation of traffic flows
      (presence, absence, amount, direction, and frequency).  See
      [RFC4949].









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8.  Security Considerations

   This document describes privacy aspects that protocol designers
   should consider in addition to regular security analysis.















































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9.  IANA Considerations

   This document does not require actions by IANA.
















































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10.  Acknowledgements

   We would like to thank the participants for the feedback they
   provided during the December 2010 Internet Privacy workshop co-
   organized by MIT, ISOC, W3C and the IAB.














































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11.  References

11.1.  Normative References

   [I-D.iab-privacy-terminology]
              Hansen, M., Tschofenig, H., and R. Smith, "Privacy
              Terminology", draft-iab-privacy-terminology-00 (work in
              progress), January 2012.

11.2.  Informative References

   [EFF]      Electronic Frontier Foundation, "Panopticlick", 2011.

   [OECD]     Organization for Economic Co-operation and Development,
              "OECD Guidelines on the Protection of Privacy and
              Transborder Flows of Personal Data", available at
              (September 2010) , http://www.oecd.org/EN/document/
              0,,EN-document-0-nodirectorate-no-24-10255-0,00.html,
              1980.

   [PbD]      Office of the Information and Privacy Commissioner,
              Ontario, Canada, "Privacy by Design", 2011.

   [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.

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              November 2002.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [RFC4101]  Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101,
              June 2005.

   [RFC4918]  Dusseault, L., "HTTP Extensions for Web Distributed
              Authoring and Versioning (WebDAV)", RFC 4918, June 2007.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              RFC 4949, August 2007.

   [RFC5025]  Rosenberg, J., "Presence Authorization Rules", RFC 5025,
              December 2007.




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   [RFC6280]  Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
              Tschofenig, H., and H. Schulzrinne, "An Architecture for
              Location and Location Privacy in Internet Applications",
              BCP 160, RFC 6280, July 2011.

   [Solove]   Solove, D., "Understanding Privacy", 2010.

   [Tor]      The Tor Project, Inc., "Tor", 2011.











































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Authors' Addresses

   Alissa Cooper
   CDT
   1634 Eye St. NW, Suite 1100
   Washington, DC  20006
   US

   Phone: +1-202-637-9800
   Email: acooper@cdt.org
   URI:   http://www.cdt.org/


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at


   Bernard Aboba
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   US

   Email: bernarda@microsoft.com


   Jon Peterson
   NeuStar, Inc.
   1800 Sutter St Suite 570
   Concord, CA  94520
   US

   Email: jon.peterson@neustar.biz


   John B. Morris, Jr.

   Email: ietf@jmorris.org






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