Network Working Group W. Haddad
Internet-Draft Ericsson Research
Expires: December 28, 2006 E. Nordmark
Sun Microsystems
June 26, 2006
Privacy Aspects Terminology
draft-haddad-alien-privacy-terminology-01
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Copyright (C) The Internet Society (2006).
Abstract
This memo introduces the 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
confusion.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. General Terminology . . . . . . . . . . . . . . . . . . . . . 5
4. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Location Privacy . . . . . . . . . . . . . . . . . . . . . . . 7
6. Overview of Different Privacy Aspects . . . . . . . . . . . . 8
6.1. Anonymity . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Unlinkability . . . . . . . . . . . . . . . . . . . . . . 8
6.3. Unobservability . . . . . . . . . . . . . . . . . . . . . 9
6.4. Relation Between Anonymity and Unlinkability . . . . . . . 9
6.5. Pseudonymity . . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 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 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 the 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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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.
Knowledge
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.
We refer to any prior information available to an attacker about a
specific target as background knowledge.
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4. Privacy
Privacy is a fundamental human right. The most common definition of
privacy is the one by Alan Westin: "Pivacy is the claim of
individuals, groups and institutions to determine for themesleves,
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
performed.
The main prvacy aspects are anonymity, unlinkability,
unobservability, and pseudonymity. Note that privacy can be achieved
by disconnectivity, i.e., not being connected to a network.
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5. 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
information.
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. 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.
6.1. Anonymity
Anonymity is the state of being not uniquely characterized, i.e.,
identifiable, within a set of subjects (e.g., node, user) called the
anonymity set. The set of possible subjects depends on the knowledge
of the attacker and may vary overtime. Thus, anonymity is relative
with respect to the attacker and 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
identity.
6.2. 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 concerning his background
knowledge.
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
received by the same recipient is the same as the probability imposed
by his a-priori knowledge.
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.
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6.3. Unobservability
Unobservability is the state of IOIs being indistinguishable from any
IOI. This means that messages are not discernable from e.g., random
noise. Consequently, unobservability deals with events instead of
subjects.
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.
6.4. Relation Between Anonymity and Unlinkability
In terms of unlinkability, anonymity can be defined as the
unlikability of an IOI and any identifier of a subject.
Consequently, unlinkability is a sufficient condition of anonymity
but is not a necessary condition.
6.5. Pseudonymity
Pseudonymity is a weaker property related to anonymity. 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.
From a user perspective, pseudonymity ensures that a user may use a
resource or service without disclosing its user identity, but can
still be accountable for that use.
Consequently, a pseudonym is an identifier for a party to a
transaction, which is not in the normal course of events, sufficient
to associate the transaction with a particular user.
Hence a transaction is pseudonymous in relation to a particular party
if the transaction data contains no direct identifier for that party,
and can only be related to them in the event that a very specific
piece of additional data is associated with it.
For more literature about the privacy terminology content, please
refer to [ANON], [ISO99], [PRIVNG], [FREEDOM] and [ANON-PRIV].
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7. Security Considerations
This document introduces terminology for different privacy aspects.
It does not raise any security issues.
8. References
[ANON] Pfitzman, A. and M. Hansen, "Anonymity, Unlinkability,
Unobservability, Pseudonymity, and Identity Management - A
consolidated Proposal for Terminology", Draft v0.28,
May 2006.
[ANON-PRIV]
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
Ericsson Research
Torshamnsgatan 23
SE-164 Stockholm
Sweden
Phone: +46 84044079
Email: Wassim.Haddad@ericsson.com
Erik Nordmark
Sun Microsystems
17 Network Circle
Menlo Park, CA 94025
USA
Phone: +1 650 786 2921
Email: Erik.Nordmark@sun.com
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