Network Working Group J. Arkko
Internet-Draft Ericsson
Intended status: Informational March 14, 2023
Expires: September 15, 2023
Data minimization among protocol participants
draft-arkko-iab-data-minimization-principle-04
Abstract
Communications security has been at the center of many security
improvements in the Internet. The goal has been to ensure that
communications are protected against outside observers and attackers.
Privacy has also been a key focus area, and understanding the privacy
implications of new Internet technology is an important factor when
IETF works on such technologies. One key aspect of privacy is
minimization of data disclosed to other parties.
This document highlights the need for a particular focus with respect
to data minimization. Avoiding data leakage to outside parties is of
course important, but it can also be necessary to limit it among the
primary protocol participants.
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.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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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 15, 2023.
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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
(http://trustee.ietf.org/license-info) in effect on the date of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Types of information . . . . . . . . . . . . . . . . . . 4
2.2. Dealing with compromise . . . . . . . . . . . . . . . . . 4
2.3. Related work . . . . . . . . . . . . . . . . . . . . . . 5
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
4. Informative References . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Communications security has been at the center of many security
improvements on the Internet. The goal has been to ensure that
communications are protected against outside observers and attackers.
This has been exemplified in many aspects of IETF efforts, in the
threat models [RFC3552], concerns about surveillance [RFC7258], IAB
statements [Confidentiality], and the introduction of encryption in
many protocols [RFC9000], [RFC7858], [RFC8484]. This has been very
successful. Advances in protecting most of our communications with
strong cryptographic has resulted in much improved security. Work on
these advances continues to be a key part of IETF's security effort.
Privacy has also been at the center of many activities in the IETF.
Improvements in communications security obviously have improved
privacy as well, but the concept is broader. 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.
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One key aspect of privacy is minimization of data disclosed to other
parties.
This document highlights the need for a particular focus with respect
to data minimization. Avoiding data leakage to outside parties is of
course important, but it can also be necessary to limit it among the
primary protocol participants (and not just observers/attackers). 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."
This document offers some further discussion and motivation 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. This document also suggests that what
information is given to any other participant should depend on the
role of that participant.
The reason why this is important is that it is possible that
endpoints are compromised, malicious, or have interests that do not
align with the interests of users. 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:
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"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.
Information sharing may relate to different types of protocol
exchanges, e.g., interaction of an endpoint with the network or with
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, 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.
Of course, participants may provide more information to each after
careful consideration, e.g., information provided in exchange of some
benefit, or to parties that are trusted by the participant.
2.1. 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 ([RFC6973]). Information may also be combined from multiple
sources, e.g., websites and social media systems collaborating to
identify visiting users [WP2021].
2.2. Dealing with compromise
Even with careful exposure of information, compromises may occur. It
is important to build defenses to protect information, even when some
component in a system becomes compromised. This may involve designs
where no single party has all information such as with Oblivious DNS
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[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], service
side encryption of data at rest, confidential computing, and other
mechanisms.
Protocols can ensure that forward secrecy is provided, so that the
damage resulting from a compromise of keying material has limited
impact.
On the client side, the client may trust that another party handles
information appropriately, but take steps to ensure or verify that
this is the case. For instance, as discussed above, the client can
encrypt a message only to the actual final recipient, even if the
server holds the message before it is delivered.
A corollary of the recommendation is 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.
For instance, 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. For instance, 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.
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.
2.3. Related work
Cooper et al. [RFC6973] discuss the general concept of privacy,
including data minimization. Section 6.1 in RFC 6973 is about data
minimization, and there they provide the general statement quoted in
Section 1. That is exactly about what the present document is also
about. Section 7 in RFC 6973 is about guidelines to authors of
specifications. And Section 7.1 in turn asks the a number of
questions that protocol designers can use to further analyse the
impact of their design. For data minimization the questions relate
to identifiers, data, 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. For the
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present document this is the particularly important question in RFC
6973:
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?
These questions are in line with avoiding sharing information to a
protocol participant unless it is needed for its role. Therefore,
this too is exactly what the present document is about. It is clear
from both the text and interviewing the authors of RFC 6973 that they
believed in the importance of limiting data disclosure across all
possible parties, from outsiders to the primary protocol
participants, just as the author of the current document does.
However, if there's something to be wished, RFC 6973 could perhaps
been more explicit:
o It should be stated that information should not even be shared
with a participant if it is not necessary for the expected role of
that participant. Yet, RFC 6973 says "Limiting the data collected
by protocol elements to only what is necessary (collection
limitation)". But when there are potentially conflicting
interests among the protocol participants, expecting a participant
to limit its data collection itself seems insufficient. What we
need to do is to not even give that that participant the
information. Interviewing the authors of the RFC, this what the
intent of the text was, but the text isn't explicit about it.
o Similarly, the Section 7.1 guidance is merely questions, not
recommendations about limiting to the necessary information.
o The examples in Section 6 are largely related to cases where some
information is relayed to some parties but not others. For
instance, the anonymity and identity confidentiality examples are
about withholding identity from some parties such as the other
endpoint of a call or outsiders observing an authentication
exchange. But they still disclose an identity to a party running
a service. This is of course necessary in many situations, but it
would be useful to provide examples where information is withheld
entirely.
These are of course nuances that may change in a future revision of
RFC 6973.
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In the years after publishing [RFC6973] there has also been a number
of documents on specific issues, 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] discusses 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. The document recommends a principle that implicit
signals should be avoided and that explicit signals be used instead,
and only when the signal's originator intends that it be used by the
network elements on the path.
Arkko, Kuhlewind, Pauly, and Hardie
[I-D.iab-path-signals-collaboration] discuss the same topic, and
extend the RFC 8558 principles with recommendations to ensure minimum
set of parties, minimum information, and consent.
Kuehlewind, 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. This is of course a highly relevant technique, and
should be a part of the data minimization toolkit.
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, e.g., deliberate selection of protocol
participants or limiting the capabilities or information exposure
related to the intermediaries.
Trammel and Kuehlewind [RFC8546] discuss the concept of a "wire
image" of a protocol. This is an abstraction of the information
available to an on-path non-participant in a networking protocol. It
relates to the topic of non-participants interpreting information
that is available to them in the "wire image" (or associated timing
and other indirect information). The issues are largely the same
even for participants. Even proper protocol participants may start
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to use information available to them, regardless of whether it was
intended to that participant or simply relayed through them.
3. 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 Kuehlewind, Tommy Pauly, Jaime Jimenez
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],
4. 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", draft-
annee-dprive-oblivious-dns-00 (work in progress), 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", draft-arkko-arch-internet-threat-model-
guidance-00 (work in progress), July 2021,
<https://datatracker.ietf.org/doc/html/draft-arkko-arch-
internet-threat-model-guidance-00>.
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[I-D.farrell-etm]
Farrell, S., "We're gonna need a bigger threat model",
draft-farrell-etm-03 (work in progress), 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. Kuehlewind,
"Considerations on Application - Network Collaboration
Using Path Signals", draft-iab-path-signals-
collaboration-03 (work in progress), February 2023,
<https://datatracker.ietf.org/doc/html/draft-iab-path-
signals-collaboration-03>.
[I-D.iab-privacy-partitioning]
Kuehlewind, M., Pauly, T., and C. Wood, "Partitioning as
an Architecture for Privacy", draft-iab-privacy-
partitioning-01 (work in progress), 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", draft-iab-use-it-or-lose-it-04
(work in progress), 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. Wood, "Oblivious HTTP", draft-ietf-
ohai-ohttp-07 (work in progress), March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-ohai-
ohttp-07>.
[I-D.ietf-ppm-dap]
Geoghegan, T., Patton, C., Rescorla, E., and C. Wood,
"Distributed Aggregation Protocol for Privacy Preserving
Measurement", draft-ietf-ppm-dap-04 (work in progress),
March 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-ppm-dap-04>.
[I-D.lazanski-smart-users-internet]
Lazanski, D., "An Internet for Users Again", draft-
lazanski-smart-users-internet-00 (work in progress), July
2019, <https://datatracker.ietf.org/doc/html/draft-
lazanski-smart-users-internet-00>.
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[I-D.pauly-dprive-oblivious-doh]
Kinnear, E., McManus, P., Pauly, T., Verma, T., and C.
Wood, "Oblivious DNS over HTTPS", draft-pauly-dprive-
oblivious-doh-11 (work in progress), 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", draft-thomson-
tmi-04 (work in progress), September 2022,
<https://datatracker.ietf.org/doc/html/draft-thomson-tmi-
04>.
[I-D.wood-pearg-website-fingerprinting]
Goldberg, I., Wang, T., and C. Wood, "Network-Based
Website Fingerprinting", draft-wood-pearg-website-
fingerprinting-00 (work in progress), 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.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003, <https://www.rfc-
editor.org/info/rfc3552>.
[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>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[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>.
[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>.
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[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>.
[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>.
[WP2021] Fowler, Geoffrey., "There's no escape from Facebook, even
if you don't use it", Washington Post , August 2021.
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Author's Address
Jari Arkko
Ericsson
Valitie 1B
Kauniainen
Finland
Email: jari.arkko@piuha.net
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