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Network Working Group                                          W. Haddad
Internet-Draft                                                  Ericsson
Intended status: Informational                               E. Nordmark
Expires: May 15, 2011                                             Oracle
                                                       November 11, 2010

                      Privacy Aspects Terminology


   This memo introduces terminology for the main privacy aspects.  The
   prime goal is to avoid situations where different interpretations of
   the same key privacy aspects result in different requirements when
   designing specific solutions, thus leading to an unnecessary

Status of this Memo

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   This Internet-Draft will expire on May 15, 2011.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document  . . . . . . . . . . . . . .  4
   3.  General Terminology  . . . . . . . . . . . . . . . . . . . . .  5
   4.  Privacy  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Overview of Different Privacy Aspects  . . . . . . . . . . . .  7
     5.1.  Anonymity  . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.2.  Unlinkability  . . . . . . . . . . . . . . . . . . . . . .  7
     5.3.  Relation Between Anonymity and Unlinkability . . . . . . .  8
     5.4.  Undetectability and Unobservability  . . . . . . . . . . .  8
     5.5.  Pseudonymity . . . . . . . . . . . . . . . . . . . . . . .  9
     5.6.  Location Privacy . . . . . . . . . . . . . . . . . . . . .  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   7.  Informative References . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1.  Introduction

   Privacy is becoming a key requirement to allow deployment of specific
   internet services.  However, privacy has many aspects, which differ
   in scope, properties and limitations.

   To avoid any possible confusion in ongoing and future works with
   regard to the meanings of privacy in some particular scenarios, and
   to differentiate between requirements related to each scenario,
   privacy aspects have to be well defined before designing any
   solution.  It is the intention of this memo to introduce terminology
   for the main aspects of privacy.

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2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [TERM].

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3.  General Terminology

   Item of Interest (IOI)

      An Item of Interest (IOI) represents what an attacker is trying to
      discover, learn, trace and possibly link to other IOI(s), in order
      to identify its target.  Examples of IOI include a subject, event,
      action (e.g., send, receive, move, etc), specific type of
      messages, etc.


      In the field of privacy, knowledge refers to the information
      available to an attacker about its target.  In terms of IOI,
      knowledge can be described by the probability of one or more IOIs.
      Consequently, more knowledge means more accurate probabilities.
      We refer to any prior information available to an attacker about a
      specific target as background knowledge.


      A pseudonym is an identifier of a subject (e.g., user) to a
      particular transaction, which is different than any of the user's
      real names.  This means that in the normal course of events, a
      pseudonym is not sufficient to associate the transaction to a
      particular subject.

   Digital Pseudonym

      A digital pseudonym is a unique identifier (at least with very
      high probability) suitable to be used to authenticate the holder's
      IOIs relatively to his/her digital pseudonym, e.g., to
      authenticate his/her messages sent.
      Another utility example is to set up an online account with an
      organization without revealing personal information, e.g., a
      public key.
      Note that using digital pseudonyms, accountability can be realized
      with respect to pseudonyms.

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4.  Privacy

   Privacy is a fundamental human right.  The most common definition of
   privacy is the one by Alan Westin: "Privacy is the claim of
   individuals, groups and institutions to determine for themselves,
   when, how and to what extent information about them is communicated
   to others".

   Privacy is a general term that involves several different aspects.
   These aspects enable features like hiding the node's address(es)
   (e.g., MAC and/or IP), name(s) (e.g., DNS), and/or location(s), in
   addition to hiding specific IOIs.  One or more of these features can
   be obtained during one particular session.

   In wireless telecommunications, privacy addresses especially the
   protection of the content as well as the context (e.g., time,
   location, type of service, ...) of a communication event.

   Consequently, neither the mobile node nor its system software shall
   support the creation of user-related usage profiles.  Such profiles
   basically comprise of a correlation of time and location of the
   node's use, as well as the type and details of the transaction

   The main prvacy aspects are anonymity, unlinkability,
   undetectability, unobservability, and pseudonymity.  Note that one
   way to achieve privacy is by disconnectivity, i.e., not being
   connected to a network.

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5.  Overview of Different Privacy Aspects

   As mentioned above, privacy is a general term, which refers to many
   different aspects.  In the following, we define the main privacy
   aspects and describe the different relations between them.

5.1.  Anonymity

   Anonymity is the state of being not identifiable within a set of
   subjects (e.g., node, user) called anonymity set.  The sender(s)
   anonymity set(s) can be the same as the recipient(s) anonymity set(s)
   or they can overlap or simply be disjoint.  But it should be noted
   that a set of possible subjects depends only on the knowledge of the
   attacker and may vary overtime.  However, as the attacker's knowledge
   is expected to only increase in most applications, this means that
   the anonymity set can only decrease.  Consequently, anonymity is the
   stronger, the larger the respective anonymity set is.  Following the
   above description, it becomes clear that the anonymity concept is
   very much context dependent.

   In the security field, anonymity is a property of network security.
   An entity "A" in a set has anonymity if no other entity can identify
   "A", nor is there any link back to "A" that can be used, nor any way
   to verify that any two anonymous act are performed by "A".

   From a user perspective, anonymity ensures that a user may use a
   resource or service without disclosing the user's identity.

   In wireless networks, anonymity means that neither the mobile node
   nor its system shall by default expose any information that allows
   any conclusions on the owner or current use of the node.

   Consequently, in scenarios where a device and/or network identifiers
   are used (e.g., MAC address, IP address), neither the communication
   partner nor any outside attacker should be able to disclose any
   possible link between the respective identifier and the user's

5.2.  Unlinkability

   Unlinkability of two or more IOIs means that from an attacker's
   perspective, these IOIs are no more and no less related after his
   observation than they are related with regards to his background

   For example, two messages (e.g., binding updates) are unlinkable for
   an attacker if the a-posteriori probability describing his background
   knowledge that these two messages are sent by the same sender and/or

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   received by the same recipient is the same as the probability imposed
   by his a-priori knowledge (i.e., by observing the system).

   From a user perspective, unlinkability ensures that a user may make
   multiple uses of resources or services without other being able to
   link these uses together.

5.3.  Relation Between Anonymity and Unlinkability

   In terms of unlinkability, anonymity can be defined as the
   unlinkability of an IOI and any subject.  For example, a sender
   anonymity means that a particular message is not linkable to any
   sender and that to a particular sender, no message is linkable.  The
   same is true for recipient anonymity.

   If we consider as an example, that the subject is a pseudonym, this
   means that the anonymity of a particular IOI can be defined as the
   unlinkability of the IOI to any pseudonym and an anonymous pseudonym
   is not linkable to any IOI.

   A weaker property than the sender's anonymity and the recipient's
   anonymity is the "relationship anonymity" where two or more
   pseudonyms are unlinkable.  This means that for senders and
   recipients, it is not possible to trace who is communicating with
   whom, though it may possible to trace who is the sender, or who is
   the recipient.  In other words, sender's pseudonyms and recipient's
   pseudonyms are unlinkable.

5.4.  Undetectability and Unobservability

   As described above, the anonymity and unlinkability states protect
   the relationship between an IOI and a subject(s) or other IOI(s).
   This means that in scenarios where anonymity and/or unlinkability are
   required, senders and recipients can still exchange unprotected

   In contrast to anonymity and unlinkability, the undetectability of
   IOIs is the state that whether they exist or not is
   indistinguishable.  In other words, undetectability protects IOIs
   from being exposed.  That is, the message transmission is not
   discernable from a random noise.  In addition, unlinkability does not
   mention any relationship between "could-be" IOIs and subjects causing
   them.  Consequently, undetectability of an IOI cannot be achieved if
   the IOI is related to a subject(s).

   On the other side, unobservability can be defined as the
   undetectability by unrelated subjects together with anonymity (even
   if an IOIs can be detected).

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   From a user perspective, unobservability ensures that a user may use
   a resource or service without others, especially third parties, being
   able to observe that the resource or service is being used.

5.5.  Pseudonymity

   Pseudonymity is a weaker property related to anonymity as it means
   that one cannot identify an entity, but it may be possible to prove
   that two pseudonyms acts were performed by the same entity.

   When digital pseudonyms are used, pseudonymity ensures that a user
   may use a resource or service without disclosing its user identity,
   but can still be accountable for that use.

   For more literature about the privacy terminology content, please
   refer to [ANON], [ISO99], [PRIVNG], [FREEDOM] and [ANONP].

5.6.  Location Privacy

   Location privacy is the ability to prevent other parties from
   learning one's current and/or past location.  In order to get such
   ability, the concerned (i.e., targeted) node must conceal any
   relation between its location and the personal identifiable

   In other words, when the location is considered an IOI, then location
   privacy means the unlinkability between a node's identity and its

   In our context, location privacy refers normally to the topological
   location and not the geographic one.  The latter is provided by other
   means (e.g., GPS) than an IPv6 address.  But it should be noted that
   it may be possible sometimes to deduce the geographical location from
   the topological one.

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6.  Security Considerations

   This document introduces terminology for different privacy aspects.
   It does not raise any security issues.

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7.  Informative References

   [ANON]     Pfitzman, A. and M. Hansen, "Anonymity, Unlinkability,
              Unobservability, Pseudonymity, and Identity Management - A
              consolidated Proposal for Terminology", Draft v0.31,
              February 2008.

   [ANONP]    Schmidt, M., "Subscriptionless Mobile Networking:
              Anonymity and Privacy Aspects within Personal Area
              Networks", IEEE WCNC, 2002.

   [FREEDOM]  Westin, A., "Privacy and Freedom", Atheneum Press,
              NY, USA, 1967.

   [ISO99]    "ISO IS 15408", http://www.commoncriteria.org/ , 1997.

   [PRIVNG]   Escudero-Pascual, A., "Privacy in the Next Generation
              Internet", December 2002.

   [TERM]     Bradner, S., "Key Words for Use in RFCs to Indicate
              Requirement Levels", RFC 2119, BCP , March 1997.

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Authors' Addresses

   Wassim Haddad
   300 Holger Way
   San Jose, CA  95134

   Phone: +1 646 2562030
   Email: Wassim.Haddad@ericsson.com

   Erik Nordmark
   17 Network Circle
   Menlo Park, CA 94025

   Phone: +1 650 786 2921
   Email: Erik.Nordmark@oracle.com

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