Internet DRAFT - draft-arkko-iab-data-minimization-principle
draft-arkko-iab-data-minimization-principle
Network Working Group J. Arkko
Internet-Draft Ericsson
Intended status: Informational July 2023
Expires: 11 January 2024
Emphasizing data minimization among protocol participants
draft-arkko-iab-data-minimization-principle-05
Abstract
Data minimization is an important privacy technique, as it can reduce
the amount information exposed about a user. This document
emphasizes the need for data minimization among primary protocol
participants, such as between clients and servers. Avoiding data
leakage to outside parties is of course very important as well, but
both need to be considered in minimization.
This is because is necessary to protect against endpoints that are
compromised, malicious, or whose interests simply do not align with
the interests of users. It is important to consider the role of a
participant and limit any data provided to it according to that role.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 2 January 2024.
Copyright Notice
Copyright (c) 2023 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Types of Protocol Exchanges . . . . . . . . . . . . . . . 4
3.2. Types of information . . . . . . . . . . . . . . . . . . 4
3.3. Different Ways of Avoiding Information Sharing . . . . . 4
3.4. Role of Trust . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Evolvability and Fingerprinting . . . . . . . . . . . . . 5
3.6. Related work . . . . . . . . . . . . . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
5. Informative References . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Privacy been at the center of many activities in the IETF. Privacy
and its impact on protocol development activities at IETF is
discussed in [RFC6973], covering a number of topics, from
understanding privacy threats to threat mitigation, including data
minimization.
This document emphasizes the need for data minimization among primary
protocol participants, such as between clients and servers. Avoiding
data leakage to outside parties such as observers or attackers is of
course very important as well, but minimization needs to consider
both.
As RFC 6973 states:
"Limiting the data collected by protocol elements to
only what is necessary (collection limitation) is
the most straightforward way to help reduce privacy
risks associated with the use of the protocol."
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This document offers some further discussion, recommendations, and
clarifications for this. This document suggests that limiting the
sharing of data to the protocol participants is a key technique in
limiting the data collection mentioned above. It is important that
minimization happens prior to disclosing information to another
party, rather than relying on the good will of the other party to
avoid storing the information.
This is because is necessary to protect against endpoints that are
compromised, malicious, or whose interests simply do not align with
the interests of users. It is important to consider the role of a
participant and limit any data provided to it according to that role.
Even closed, managed networks may have compromised nodes, justifying
careful consideration of what information is provided to different
nodes in the network. And in all networks, increased use of
communication security means adversaries may resort to new avenues of
attack. New adversaries and risks have also arisen, e.g., due to
increasing amount of information stored in various Internet services.
And in situations where interests do not align across the protocol
participants, limiting data collection by a protocol participant
itself - who is interested in data collection - may not be
sufficient.
Careful control of information is also useful for technology
evolution. For instance, allowing a party to unnecessarily collect
or receive information may lead to a similar effect as described in
[RFC8546] for protocols: regardless of initial expectations, over
time unnecessary information will get used, leading to, for instance,
ossification. Systems end up depend on having access to exactly the
same information as they had access to previously. This makes it
hard to change what information is provided or how it is provided.
2. Recommendations
The Principle of Least Privilege [PoLP] is applicable:
"Every program and every user of the system should operate
using the least set of privileges necessary to complete the
job."
In this context, it is recommended that the protocol participants
minimize the information they share. I.e., they should provide only
the information to each other that is necessary for the function that
is expected to be performed by the other party.
3. Discussion
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3.1. Types of Protocol Exchanges
Information sharing may relate to different types of protocol
exchanges, e.g., interaction of an endpoint with outsiders, the
network, or intermediaries.
Other documents address aspects related to networks ([RFC8546],
[RFC8558], [I-D.iab-path-signals-collaboration]). Thomson
[I-D.thomson-tmi] discusses the role intermediaries. Communications
security largely addresses observers and outsider adversaries, see
for instance [Confidentiality], [RFC7858], [RFC8446], [RFC8484],
[RFC9000]. And [RFC6973] discusses associated traffic analysis
threats.
The focus in this document is on the primary protocol participants,
such as a server in a client-server architecture or a service enables
some kind of interaction among groups of users.
As with communication security, we try to avoid providing too much
information as it may be misused or leak through attacks. The same
principle applies not just to routers and potential attackers on
path, but also many other services in the Internet, including servers
that provide some function.
3.2. Types of information
The use of identifiers has been extensively discussed in [RFC6973],
Note that indirectly inferred information can also end up being
shared, such as message arrival times or patterns in the traffic flow
([RFC6973]). Information may also be obtained from fingerprinting
the protocol participants, in an effort to identify unique endpoints
or users. Information may also be combined from multiple sources,
e.g., websites and social media systems collaborating to identify
visiting users [WP2021].
3.3. Different Ways of Avoiding Information Sharing
The most straightforward approach is of course to avoid sending a
particular piece of information at all.
Or the information needs to be encrypted to very specific recipients,
even if the encrypted message is shared with a broader set of
protocol participants. For instance, a client can encrypt a message
only to the actual final recipient, even if the server holds the
message before it is delivered.
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Architectural note: A transport connection between
two components of a system is not an end-to-end
connection even if it encompasses all the protocol
layers up to the application layer. It is not
end-to-end, if the information or control function
it carries extends beyond those components. Just
because an e-mail server can read the contents of
an e-mail message do not make it a legitimate
recipient of the e-mail.
This document recommends that information should not be disclosed,
stored, or routed in cleartext through services that do not need to
have that information for the function they perform.
Where the above methods are not possible due to the information being
necessary for a function that the user wishes to be performed, there
are still methods to set limits on the information sharing.
Kühlewind et al discuss the concept of Privacy Partititioning
[I-D.iab-privacy-partitioning]. This may involve designs where no
single party has all information such as with Oblivious DNS
[I-D.annee-dprive-oblivious-dns], [I-D.pauly-dprive-oblivious-doh] or
HTTP [I-D.ietf-ohai-ohttp], cryptographic designs where a service
such as with the recent IETF PPM effort [I-D.ietf-ppm-dap], and so
on.
3.4. Role of Trust
Of course, participants may provide more information to each other
after careful consideration, e.g., information provided in exchange
of some benefit, or to parties that are trusted by the participant.
3.5. Evolvability and Fingerprinting
The general topic of ensuring that protocol mechanisms stays
evolvable and workable is covered in [I-D.iab-use-it-or-lose-it].
But the associated methods for reducing fingerprinting possibilities
probably deserve further study [Fingerprinting] [AmIUnique].
[I-D.wood-pearg-website-fingerprinting] discusses one aspect of this.
3.6. Related work
Cooper et al. [RFC6973] discuss the general concept of privacy,
including data minimization. Among other things, it provides the
general statement quoted in Section 1. It also provides guidelines
to authors of specifications, a number of questions that protocol
designers can use to further analyze the impact of their design. For
data minimization the questions relate to identifiers, data,
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observers, and fingerprinting. This includes, for instance, asking
what information is exposed to which protocol entities, and if there
are ways to limit such exposure:
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?
This is very much in line with this document, although today it would
be desirable to have recommendation as well as questions. For
instance, recommending against sharing information with a participant
if it is not necessary for the expected role of that participant.
And, as discussed earlier, it is important to distinguish between the
choices of a sender not sharing information and a receiver choosing
to not collect information. Trusting an entity to not collect is not
sufficient.
There has also been a number of documents that address data
minimization for specific situations, such as one DNS Query Name
Minimization [RFC7816], general DNS privacy advice including data
minimization [RFC9076], advice for DHCP clients for minimizing
information in requests they send to DHCP servers [RFC7844] (along
with general privacy considerations of DHCP [RFC7819] [RFC7824]).
These are on the topic of limiting information sent by one primary
protocol particiant (client) to another (server).
Hardie [RFC8558] and Arkko et al.
[I-D.iab-path-signals-collaboration] discuss path signals, i.e.,
messages to or from on-path elements to endpoints. In the past, path
signals were often implicit, e.g., network nodes interpreting in a
particular way transport protocol headers originally intended for
end-to-end consumption. Implicit signals should be avoided and that
explicit signals be used instead.
Kühlewind, Pauly, and Wood [I-D.iab-privacy-partitioning] discuss the
concept of privacy partitioning: how information can be split and
carefully shared in ways where no individual party beyond the client
requesting a service has full picture of who is asking and what is
being asked.
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Thomson [I-D.thomson-tmi] discusses the role intermediaries in the
Internet architecture, at different layers of the stack. For
instance, a router is an intermediary, some parts of DNS
infrastructure can be intermediaries, messaging gateways are
intermediaries. Thomson discusses when intermediaries are or are not
an appropriate tool and presents a number of principles relating to
the use of intermediaries.
Trammel and Kühlewind [RFC8546] discuss the concept of a “wire image”
of a protocol, and how network elements may start to rely on
information in the image, even if it was not originally intended for
them. The issues are largely the same even for participants.
4. Acknowledgements
The author would like to thank the participants of various IAB
workshops and programs, and IETF discussion list contributors for
interesting discussions in this area. The author would in particular
like to acknowledge the significant contributions of Martin Thomson,
Nick Doty, Alissa Cooper, Stephen Farrell, Mark McFadden, John
Mattsson, Chris Wood, Dominique Lazanski, Eric Rescorla, Russ
Housley, Robin Wilton, Mirja Kühlewind, Tommy Pauly, Jaime Jiménez
and Christian Huitema.
This work has been influenced by [RFC6973], [RFC8980],
[I-D.farrell-etm] [I-D.arkko-arch-internet-threat-model-guidance],
[I-D.lazanski-smart-users-internet],
5. Informative References
[AmIUnique]
INRIA, ., "Am I Unique?", https://amiunique.org , 2020.
[Confidentiality]
The Internet Architecture Board, ., "IAB Statement on
Internet Confidentiality", https://www.iab.org/2014/11/14/
iab-statement-on-internet-confidentiality/ , November
2014.
[Fingerprinting]
Laperdrix, P., Bielova, N., Baudry, B., and G. Avoine,
"Browser Fingerprinting: A survey", arXiv:1905.01051v2
[cs.CR] 4 Nov 2019 , November 2019.
[I-D.annee-dprive-oblivious-dns]
Edmundson, A., Schmitt, P., Feamster, N., and A. Mankin,
"Oblivious DNS - Strong Privacy for DNS Queries", Work in
Progress, Internet-Draft, draft-annee-dprive-oblivious-
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dns-00, 2 July 2018,
<https://datatracker.ietf.org/doc/html/draft-annee-dprive-
oblivious-dns-00>.
[I-D.arkko-arch-internet-threat-model-guidance]
Arkko, J. and S. Farrell, "Internet Threat Model
Guidance", Work in Progress, Internet-Draft, draft-arkko-
arch-internet-threat-model-guidance-00, 12 July 2021,
<https://datatracker.ietf.org/doc/html/draft-arkko-arch-
internet-threat-model-guidance-00>.
[I-D.farrell-etm]
Farrell, S., "We're gonna need a bigger threat model",
Work in Progress, Internet-Draft, draft-farrell-etm-03, 6
July 2019, <https://datatracker.ietf.org/doc/html/draft-
farrell-etm-03>.
[I-D.iab-path-signals-collaboration]
Arkko, J., Hardie, T., Pauly, T., and M. Kühlewind,
"Considerations on Application - Network Collaboration
Using Path Signals", Work in Progress, Internet-Draft,
draft-iab-path-signals-collaboration-03, 3 February 2023,
<https://datatracker.ietf.org/doc/html/draft-iab-path-
signals-collaboration-03>.
[I-D.iab-privacy-partitioning]
Kühlewind, M., Pauly, T., and C. A. Wood, "Partitioning as
an Architecture for Privacy", Work in Progress, Internet-
Draft, draft-iab-privacy-partitioning-01, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-iab-privacy-
partitioning-01>.
[I-D.iab-use-it-or-lose-it]
Thomson, M. and T. Pauly, "Long-Term Viability of Protocol
Extension Mechanisms", Work in Progress, Internet-Draft,
draft-iab-use-it-or-lose-it-04, 12 October 2021,
<https://datatracker.ietf.org/doc/html/draft-iab-use-it-
or-lose-it-04>.
[I-D.ietf-ohai-ohttp]
Thomson, M. and C. A. Wood, "Oblivious HTTP", Work in
Progress, Internet-Draft, draft-ietf-ohai-ohttp-08, 15
March 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-ohai-ohttp-08>.
[I-D.ietf-ppm-dap]
Geoghegan, T., Patton, C., Rescorla, E., and C. A. Wood,
"Distributed Aggregation Protocol for Privacy Preserving
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Measurement", Work in Progress, Internet-Draft, draft-
ietf-ppm-dap-05, 10 July 2023,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-ppm-dap/>.
[I-D.lazanski-smart-users-internet]
Lazanski, D., "An Internet for Users Again", Work in
Progress, Internet-Draft, draft-lazanski-smart-users-
internet-00, 8 July 2019,
<https://datatracker.ietf.org/doc/html/draft-lazanski-
smart-users-internet-00>.
[I-D.pauly-dprive-oblivious-doh]
Kinnear, E., McManus, P., Pauly, T., Verma, T., and C. A.
Wood, "Oblivious DNS over HTTPS", Work in Progress,
Internet-Draft, draft-pauly-dprive-oblivious-doh-11, 17
February 2022, <https://datatracker.ietf.org/doc/html/
draft-pauly-dprive-oblivious-doh-11>.
[I-D.thomson-tmi]
Thomson, M., "Principles for the Involvement of
Intermediaries in Internet Protocols", Work in Progress,
Internet-Draft, draft-thomson-tmi-04, 8 September 2022,
<https://datatracker.ietf.org/doc/html/draft-thomson-tmi-
04>.
[I-D.wood-pearg-website-fingerprinting]
Goldberg, I., Wang, T., and C. A. Wood, "Network-Based
Website Fingerprinting", Work in Progress, Internet-Draft,
draft-wood-pearg-website-fingerprinting-00, 4 November
2019, <https://datatracker.ietf.org/doc/html/draft-wood-
pearg-website-fingerprinting-00>.
[PoLP] Saltzer, J. and M. Schroader, "The Protection of
Information in Computer Systems", Fourth ACM Symposium on
Operating System Principles , October 1975.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
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[RFC7819] Jiang, S., Krishnan, S., and T. Mrugalski, "Privacy
Considerations for DHCP", RFC 7819, DOI 10.17487/RFC7819,
April 2016, <https://www.rfc-editor.org/info/rfc7819>.
[RFC7824] Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
Considerations for DHCPv6", RFC 7824,
DOI 10.17487/RFC7824, May 2016,
<https://www.rfc-editor.org/info/rfc7824>.
[RFC7844] Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
Profiles for DHCP Clients", RFC 7844,
DOI 10.17487/RFC7844, May 2016,
<https://www.rfc-editor.org/info/rfc7844>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
2019, <https://www.rfc-editor.org/info/rfc8546>.
[RFC8558] Hardie, T., Ed., "Transport Protocol Path Signals",
RFC 8558, DOI 10.17487/RFC8558, April 2019,
<https://www.rfc-editor.org/info/rfc8558>.
[RFC8980] Arkko, J. and T. Hardie, "Report from the IAB Workshop on
Design Expectations vs. Deployment Reality in Protocol
Development", RFC 8980, DOI 10.17487/RFC8980, February
2021, <https://www.rfc-editor.org/info/rfc8980>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9076] Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076,
DOI 10.17487/RFC9076, July 2021,
<https://www.rfc-editor.org/info/rfc9076>.
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[WP2021] Fowler, Geoffrey A., "There’s no escape from Facebook,
even if you don’t use it", Washington Post , August 2021.
Author's Address
Jari Arkko
Ericsson
Valitie 1B
FI- Kauniainen
Finland
Email: jari.arkko@piuha.net
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