Internet Engineering Task Force (IETF) S. Farrell
Request for Comments: 7258 Trinity College Dublin
BCP: 188 H. Tschofenig
Category: Best Current Practice ARM Ltd.
ISSN: 2070-1721 May 2014
Pervasive Monitoring Is an Attack
Abstract
Pervasive monitoring is a technical attack that should be mitigated
in the design of IETF protocols, where possible.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7258.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Pervasive Monitoring Is a Widespread Attack on Privacy
Pervasive Monitoring (PM) is widespread (and often covert)
surveillance through intrusive gathering of protocol artefacts,
including application content, or protocol metadata such as headers.
Active or passive wiretaps and traffic analysis, (e.g., correlation,
timing or measuring packet sizes), or subverting the cryptographic
keys used to secure protocols can also be used as part of pervasive
monitoring. PM is distinguished by being indiscriminate and very
large scale, rather than by introducing new types of technical
compromise.
The IETF community's technical assessment is that PM is an attack on
the privacy of Internet users and organisations. The IETF community
has expressed strong agreement that PM is an attack that needs to be
mitigated where possible, via the design of protocols that make PM
significantly more expensive or infeasible. Pervasive monitoring was
discussed at the technical plenary of the November 2013 IETF meeting
[IETF88Plenary] and then through extensive exchanges on IETF mailing
lists. This document records the IETF community's consensus and
establishes the technical nature of PM.
The term "attack" is used here in a technical sense that differs
somewhat from common English usage. In common English usage, an
attack is an aggressive action perpetrated by an opponent, intended
to enforce the opponent's will on the attacked party. The term is
used here to refer to behavior that subverts the intent of
communicating parties without the agreement of those parties. An
attack may change the content of the communication, record the
content or external characteristics of the communication, or through
correlation with other communication events, reveal information the
parties did not intend to be revealed. It may also have other
effects that similarly subvert the intent of a communicator.
[RFC4949] contains a more complete definition for the term "attack".
We also use the term in the singular here, even though PM in reality
may consist of a multifaceted set of coordinated attacks.
In particular, the term "attack", used technically, implies nothing
about the motivation of the actor mounting the attack. The
motivation for PM can range from non-targeted nation-state
surveillance, to legal but privacy-unfriendly purposes by commercial
enterprises, to illegal actions by criminals. The same techniques to
achieve PM can be used regardless of motivation. Thus, we cannot
defend against the most nefarious actors while allowing monitoring by
other actors no matter how benevolent some might consider them to be,
since the actions required of the attacker are indistinguishable from
other attacks. The motivation for PM is, therefore, not relevant for
how PM is mitigated in IETF protocols.
2. The IETF Will Work to Mitigate Pervasive Monitoring
"Mitigation" is a technical term that does not imply an ability to
completely prevent or thwart an attack. Protocols that mitigate PM
will not prevent the attack but can significantly change the threat.
(See the diagram on page 24 of RFC 4949 for how the terms "attack"
and "threat" are related.) This can significantly increase the cost
of attacking, force what was covert to be overt, or make the attack
more likely to be detected, possibly later.
IETF standards already provide mechanisms to protect Internet
communications and there are guidelines [RFC3552] for applying these
in protocol design. But those standards generally do not address PM,
the confidentiality of protocol metadata, countering traffic
analysis, or data minimisation. In all cases, there will remain some
privacy-relevant information that is inevitably disclosed by
protocols. As technology advances, techniques that were once only
available to extremely well-funded actors become more widely
accessible. Mitigating PM is therefore a protection against a wide
range of similar attacks.
It is therefore timely to revisit the security and privacy properties
of our standards. The IETF will work to mitigate the technical
aspects of PM, just as we do for protocol vulnerabilities in general.
The ways in which IETF protocols mitigate PM will change over time as
mitigation and attack techniques evolve and so are not described
here.
Those developing IETF specifications need to be able to describe how
they have considered PM, and, if the attack is relevant to the work
to be published, be able to justify related design decisions. This
does not mean a new "pervasive monitoring considerations" section is
needed in IETF documentation. It means that, if asked, there needs
to be a good answer to the question "Is pervasive monitoring relevant
to this work and if so, how has it been considered?"
In particular, architectural decisions, including which existing
technology is reused, may significantly impact the vulnerability of a
protocol to PM. Those developing IETF specifications therefore need
to consider mitigating PM when making architectural decisions.
Getting adequate, early review of architectural decisions including
whether appropriate mitigation of PM can be made is important.
Revisiting these architectural decisions late in the process is very
costly.
While PM is an attack, other forms of monitoring that might fit the
definition of PM can be beneficial and not part of any attack, e.g.,
network management functions monitor packets or flows and anti-spam
mechanisms need to see mail message content. Some monitoring can
even be part of the mitigation for PM, for example, certificate
transparency [RFC6962] involves monitoring Public Key Infrastructure
in ways that could detect some PM attack techniques. However, there
is clear potential for monitoring mechanisms to be abused for PM, so
this tension needs careful consideration in protocol design. Making
networks unmanageable to mitigate PM is not an acceptable outcome,
but ignoring PM would go against the consensus documented here. An
appropriate balance will emerge over time as real instances of this
tension are considered.
Finally, the IETF, as a standards development organisation, does not
control the implementation or deployment of our specifications
(though IETF participants do develop many implementations), nor does
the IETF standardise all layers of the protocol stack. Moreover, the
non-technical (e.g., legal and political) aspects of mitigating
pervasive monitoring are outside of the scope of the IETF. The
broader Internet community will need to step forward to tackle PM, if
it is to be fully addressed.
To summarise: current capabilities permit some actors to monitor
content and metadata across the Internet at a scale never before
seen. This pervasive monitoring is an attack on Internet privacy.
The IETF will strive to produce specifications that mitigate
pervasive monitoring attacks.
3. Process Note
In the past, architectural statements of this sort, e.g., [RFC1984]
and [RFC2804], have been published as joint products of the Internet
Engineering Steering Group (IESG) and the Internet Architecture Board
(IAB). However, since those documents were published, the IETF and
IAB have separated their publication "streams" as described in
[RFC4844] and [RFC5741]. This document was initiated after
discussions in both the IESG and IAB, but is published as an IETF-
stream consensus document, in order to ensure that it properly
reflects the consensus of the IETF community as a whole.
4. Security Considerations
This document is entirely about privacy. More information about the
relationship between security and privacy threats can be found in
[RFC6973]. Section 5.1.1 of [RFC6973] specifically addresses
surveillance as a combined security-privacy threat.
5. Acknowledgements
We would like to thank the participants of the IETF 88 technical
plenary for their feedback. Thanks in particular to the following
for useful suggestions or comments: Jari Arkko, Fred Baker, Marc
Blanchet, Tim Bray, Scott Brim, Randy Bush, Brian Carpenter, Benoit
Claise, Alissa Cooper, Dave Crocker, Spencer Dawkins, Avri Doria,
Wesley Eddy, Adrian Farrel, Joseph Lorenzo Hall, Phillip
Hallam-Baker, Ted Hardie, Sam Hartmann, Paul Hoffman, Bjoern
Hoehrmann, Russ Housley, Joel Jaeggli, Stephen Kent, Eliot Lear,
Barry Leiba, Ted Lemon, Subramanian Moonesamy, Erik Nordmark, Pete
Resnick, Peter Saint-Andre, Andrew Sullivan, Sean Turner, Nicholas
Weaver, Stefan Winter, and Lloyd Wood. Additionally, we would like
to thank all those who contributed suggestions on how to improve
Internet security and privacy or who commented on this on various
IETF mailing lists, such as the ietf@ietf.org and the
perpass@ietf.org lists.
6. Informative References
[IETF88Plenary]
IETF, "IETF 88 Plenary Meeting Materials", November 2013,
<http://www.ietf.org/proceedings/88/>.
[RFC1984] IAB, IESG, Carpenter, B., and F. Baker, "IAB and IESG
Statement on Cryptographic Technology and the Internet",
RFC 1984, August 1996.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, May
2000.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, July
2003.
[RFC4844] Daigle, L. and Internet Architecture Board, "The RFC
Series and RFC Editor", RFC 4844, July 2007.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
4949, August 2007.
[RFC5741] Daigle, L., Kolkman, O., and IAB, "RFC Streams, Headers,
and Boilerplates", RFC 5741, December 2009.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, June 2013.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, July
2013.
Authors' Addresses
Stephen Farrell
Trinity College Dublin
Dublin 2
Ireland
Phone: +353-1-896-2354
EMail: stephen.farrell@cs.tcd.ie
Hannes Tschofenig
ARM Ltd.
110 Fulbourn Rd
Cambridge CB1 9NJ
Great Britain
6060 Hall in Tirol
Austria
EMail: Hannes.tschofenig@gmx.net
URI: http://www.tschofenig.priv.at