Internet Threat Model Evolution: Background and Principles
draft-arkko-farrell-arch-model-t-redux-01
|
| Document |
Type |
|
Active Internet-Draft (individual)
|
|
Authors |
|
Jari Arkko
,
Stephen Farrell
|
|
Last updated |
|
2021-02-22
|
|
Stream |
|
(None)
|
|
Intended RFC status |
|
(None)
|
|
Formats |
|
plain text
pdf
htmlized
bibtex
|
| Stream |
Stream state |
|
(No stream defined) |
|
Consensus Boilerplate |
|
Unknown
|
|
RFC Editor Note |
|
(None)
|
| IESG |
IESG state |
|
I-D Exists
|
|
Telechat date |
|
|
|
Responsible AD |
|
(None)
|
|
Send notices to |
|
(None)
|
Network Working Group J. Arkko
Internet-Draft Ericsson
Intended status: Informational S. Farrell
Expires: August 26, 2021 Trinity College Dublin
February 22, 2021
Internet Threat Model Evolution: Background and Principles
draft-arkko-farrell-arch-model-t-redux-01
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.
This memo suggests that the existing RFC 3552 threat model, while
important and still valid, is no longer alone sufficient to cater for
the pressing security and privacy issues seen on the Internet today.
For instance, it is often also necessary to protect against endpoints
that are compromised, malicious, or whose interests simply do not
align with the interests of users. While such protection is
difficult, there are some measures that can be taken and we argue
that investigation of these issues is warranted.
It is particularly important to ensure that as we continue to develop
Internet technology, non-communications security related threats, and
privacy issues, are properly understood.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 August 26, 2021.
Arkko & Farrell Expires August 26, 2021 [Page 1]
Internet-Draft Internet Threat Model Evolution February 2021
Copyright Notice
Copyright (c) 2021 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. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Attack Landscape . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Communications Security Improvements . . . . . . . . . . 5
2.2. Beyond Communications Security . . . . . . . . . . . . . 6
2.3. Types of Attacks . . . . . . . . . . . . . . . . . . . . 7
2.3.1. Misuse of Accidental Vulnerabilities . . . . . . . . 7
2.3.2. Misbehaving Applications . . . . . . . . . . . . . . 8
2.3.3. Network Infrastructure Attacks . . . . . . . . . . . 8
2.3.4. Untrustworthy Devices . . . . . . . . . . . . . . . . 9
2.3.5. Tracking . . . . . . . . . . . . . . . . . . . . . . 10
3. Principles . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1. Trusting Devices . . . . . . . . . . . . . . . . . . . . 13
3.2. Protecting Information . . . . . . . . . . . . . . . . . 13
3.3. Tracking . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4. Role of End-to-End . . . . . . . . . . . . . . . . . . . 14
4. Security Considerations . . . . . . . . . . . . . . . . . . . 15
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6. Informative References . . . . . . . . . . . . . . . . . . . 15
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 22
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
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.
At the IETF, this approach has been formalized in BCP 72 [RFC3552],
which defined the Internet threat model in 2003.
Arkko & Farrell Expires August 26, 2021 [Page 2]
Internet-Draft Internet Threat Model Evolution February 2021
The purpose of a threat model is to outline what threats exist in
order to assist the protocol designer. But RFC 3552 also ruled some
threats to be in scope and of primary interest, and some threats out
of scope [RFC3552]:
The Internet environment has a fairly well understood threat
model. In general, we assume that the end-systems engaging in a
protocol exchange have not themselves been compromised.
Protecting against an attack when one of the end-systems has been
compromised is extraordinarily difficult. It is, however,
possible to design protocols which minimize the extent of the
damage done under these circumstances.
By contrast, we assume that the attacker has nearly complete
control of the communications channel over which the end-systems
communicate. This means that the attacker can read any PDU
(Protocol Data Unit) on the network and undetectably remove,
change, or inject forged packets onto the wire.
However, the communications-security -only threat model is becoming
outdated. Some of the causes for this are:
o Success! Advances in protecting most of our communications with
strong cryptographic means. This has resulted in much improved
communications security, but also highlights the need for
addressing other, remaining issues. This is not to say that
communications security is not important, it still is:
improvements are still needed. Not all communications have been
protected, and even out of the already protected communications,
not all of their aspects have been fully protected. Fortunately,
there are ongoing projects working on improvements.
o Adversaries have increased their pressure against other avenues of
attack, from supply-channel attacks, to compromising devices to
legal coercion of centralized endpoints in conversations.
o New adversaries and risks have arisen, e.g., due to creation of
large centralized information sources.
o While communications-security does seem to be required to protect
privacy, more is needed, especially if endpoints choose to act
against the interests of their peers or users.
In short, attacks are migrating towards the currently easier targets,
which no longer necessarily include direct attacks on traffic flows.
In addition, trading information about users and ability to influence
them has become a common practice for many Internet services, often
without users understanding those practices.
Arkko & Farrell Expires August 26, 2021 [Page 3]
Internet-Draft Internet Threat Model Evolution February 2021
This memo suggests that the existing threat model, while important
and still valid, is no longer alone sufficient to cater for the
pressing security and privacy issues on the Internet. For instance,
while it continues to be very important to protect Internet
communications against outsiders, it is also necessary to protect
systems against endpoints that are compromised, malicious, or whose
interests simply do not align with the interests of the users.
Of course, there are many trade-offs in the Internet on who one
chooses to interact with and why or how. It is not the role of this
memo to dictate those choices. But it is important that we
understand the implications of different practices. It is also
important that when it comes to basic Internet infrastructure, our
chosen technologies lead to minimal exposure with respect to the non-
communications threats.
It is particularly important to ensure that non-communications
security related threats are properly understood for any new Internet
technology. While the consideration of these issues is relatively
new in the IETF, this memo provides some initial ideas about
potential broader threat models to consider when designing protocols
for the Internet or when trying to defend against pervasive
monitoring. Further down the road, updated threat models could
result in changes in BCP 72 [RFC3552] (guidelines for writing
security considerations) and BCP 188 [RFC7258] (pervasive
monitoring), to include proper consideration of non-communications
security threats.
It may also be necessary to have dedicated guidance on how systems
design and architecture affect security. The sole consideration of
communications security aspects in designing Internet protocols may
lead to accidental or increased impact of security issues elsewhere.
For instance, allowing a participant to unnecessarily collect or
receive information may lead to a similar effect as described in
[RFC8546] for protocols: over time, unnecessary information will get
used with all the associated downsides, regardless of what deployment
expectations there were during protocol design.
This memo does not stand alone. To begin with, it is a continuation
of earlier work by the two authors [I-D.farrell-etm]
[I-D.arkko-arch-internet-threat-model]
[I-D.arkko-farrell-arch-model-t]. There are also other documents
discussing this overall space, e.g.
[I-D.lazanski-smart-users-internet] [I-D.arkko-arch-dedr-report].
The rest of this memo is organized as follows. Section 2 makes some
observations about the situation, with respect to communications
Arkko & Farrell Expires August 26, 2021 [Page 4]
Internet-Draft Internet Threat Model Evolution February 2021
security and beyond. The section also provides a number of real-
world examples.
Section 3 discusses some high-level principles that relate to these
changes, and could be used to tackle some of the emerging issues.
Comments are solicited on these and other aspects of this document.
The best place for discussion is on the model-t list.
(https://www.ietf.org/mailman/listinfo/model-t)
2. Attack Landscape
This section discusses the evolving landscape of security
vulnerabilities, threats, and attacks.
2.1. Communications Security Improvements
Being able to ask about threat model improvements is due to progress
already made: The fraction of Internet traffic that is
cryptographically protected has grown tremendously in the last few
years. Several factors have contributed to this change, from Snowden
revelations to business reasons and to better available technology
such as HTTP/2 [RFC7540], TLS 1.3 [RFC8446], QUIC
[I-D.ietf-quic-transport].
In many networks, the majority of traffic has flipped from being
cleartext to being encrypted. Reaching the level of (almost) all
traffic being encrypted is no longer something unthinkable but rather
a likely outcome in a few years.
At the same time, technology developments and policy choices have
driven the scope of cryptographic protection from protecting only the
pure payload to protecting much of the rest as well, including far
more header and meta-data information than was protected before. For
instance, efforts are ongoing in the IETF to assist encrypting
transport headers [I-D.ietf-quic-transport], server domain name
information in TLS [I-D.ietf-tls-esni], and domain name queries
[RFC8484].
There have also been improvements to ensure that the security
protocols that are in use actually have suitable credentials and that
those credentials have not been compromised, see, for instance, Let's
Encrypt [RFC8555], HSTS [RFC6797], HPKP [RFC7469], and Expect-CT
[I-D.ietf-httpbis-expect-ct].
This is not to say that all problems in communications security have
been resolved - far from it. But the situation is definitely
different from what it was a few years ago. Remaining issues will be
Arkko & Farrell Expires August 26, 2021 [Page 5]
Internet-Draft Internet Threat Model Evolution February 2021
and are worked on; the fight between defense and attack will also
continue. Communications security will stay at the top of the agenda
in any Internet technology development.
2.2. Beyond Communications Security
There are, however, significant issues beyond communications security
in the Internet.
To begin with, it is not necessarily clear that one can trust all the
endpoints in any protocol interaction, including the user's own
devices. Managed or closed ecosystems with multiple layers of
hardware and software have made it harder to understand or influence
what your devices do.
The situation is different, but not necessarily better on the side of
servers. Even for applications that are for user-to-user
communication, a typical pattern of communications is almost always
via an intermediary that has at least as much information as the
other parties have. For instance, these intermediaries are typically
endpoints for any transport layer security connections, and able to
see much communications or other messaging in cleartext. There are
some exceptions, of course, e.g., messaging applications with end-to-
end confidentiality protection.
For instance, while e-mail transport security [RFC7817] has become
much more widely deployed in recent years, progress in securing
e-mail messages between users has been much slower. This has lead to
a situation where e-mail content is considered a critical resource by
some mail service providers who use the content for machine learning,
advertisement targeting, and other purposes unrelated to message
delivery. Equally however, it is unclear how some useful anti-spam
techniques could be deployed in an end-to-end encrypted mail universe
(with today's end-to-end mail security protocols) and there are many
significant challenges should one desire to deploy end-to-end email
security at scale.
Services that are not about user-to-user to communication often
collect information about the user.
Even services that are part of the infrastructure may have security
issues. For instance, despite progress in protecting DNS query
protocols with encryption (see, e.g., [RFC7858] and [RFC8484]), DNS
resolver services themselves may be targets for attack or sources for
leaks. For instance, the services may collect information or be
vulnerable targets of denial-of-service attacks, attacks to steal
user browsing history information, or be the target of surveillance
activities and government information requests. Infrastructure
Arkko & Farrell Expires August 26, 2021 [Page 6]
Internet-Draft Internet Threat Model Evolution February 2021
services with information about a large number of users is collected
in small number of services are particularly attractive targets for
these attacks.
With the growth of trading users' information by many of these
parties, it becomes necessary to take precautions against endpoints
that are compromised, malicious, or whose interests simply do not
align with the interests of the users.
In general, many recent attacks relate more to information than
communications. For instance, personal information leaks typically
happen via information stored on a compromised server rather than
capturing communications. There is little hope that such attacks can
be prevented entirely. Again, the best course of action seems to be
avoid the disclosure of information in the first place, or at least
to not perform that in a manner that makes it possible that others
can readily use the information.
2.3. Types of Attacks
This section discusses a few classes of attacks that are relevant for
our consideration.
2.3.1. Misuse of Accidental Vulnerabilities
Not all adversarial behaviour starts as deliberate, some is initiated
due to various levels of carelessness and/or due to erroneous
assumptions about the environments in which those applications
currently run at. Nevertheless, a leak or vulnerability can be
exploited by others that misuse the data for their own purposes.
Some attacks in this category include:
o Virtualisation exposing secrets, for example, Meltdown and Spectre
[MeltdownAndSpectre] [Kocher2019] [Lipp2018] and other similar
side-channel attacks.
o Compromised badly-maintained web sites or services, e.g.,
[Passwords] or Amazon S3 leaks.
o Supply-chain attacks, for example, the [TargetAttack] or malware
within pre-installed applications on Android phones [Bloatware].
o Breaches of major service providers, that many of us might have
assumed would be sufficiently capable to be the best large-scale
"Identity providers", for example, Yahoo
(https://www.wired.com/story/yahoo-breach-three-billion-
accounts/), Facebook (https://www.pcmag.com/news/367319/facebook-
Arkko & Farrell Expires August 26, 2021 [Page 7]
Internet-Draft Internet Threat Model Evolution February 2021
stored-up-to-600m-user-passwords-in-plain-text and
https://www.cnet.com/news/facebook-breach-affected-50-million-
people/), Telcos (https://www.zdnet.com/article/us-telcos-caught-
selling-your-location-data-again-senator-demands-new-laws/ and
https://www.zdnet.com/article/millions-verizon-customer-records-
israeli-data/), Google (https://www.wsj.com/articles/google-
exposed-user-data-feared-repercussions-of-disclosing-to-public-
1539017194), and Microsoft
(https://motherboard.vice.com/en_us/article/ywyz3x/hackers-could-
read-your-hotmail-msn-outlook-microsoft-customer-support).
2.3.2. Misbehaving Applications
There are many examples of application developers doing their best to
protect the security and privacy of their users or customers. That's
just the same as the case today where we need to consider in-network
actors as potential adversaries despite the many examples of network
operators who both act in the best interests of their users and
succeed in defending against attacks from others.
In short, there are applications that do not act in the best
interests of their users.
This can also happen indirectly. Despite the best efforts of
curators, so-called App-Stores frequently distribute malware of many
kinds and one recent study [Curated] claims that simple obfuscation
enables malware to avoid detection by even sophisticated operators.
Given the scale of these deployments, distribution of even a small
percentage of malware-infected applications can affect a large number
of people. The end result is an application that
Applications may also mislead users. Many web sites today provide
some form of privacy policy and terms of service, that are known to
be mostly unread [Unread]. This implies that, legal fiction aside,
users of those sites have not in reality agreed to the specific terms
published and so users are therefore highly exposed to being
exploited by web sites, for example [Cambridge] is a recent well-
publicised case where a service provider abused the data of 87
million users via a partnership. While many web site operators claim
that they care deeply about privacy, it seems prudent to assume that
some do not in fact care about user privacy in ways with which many
of their users would agree.
2.3.3. Network Infrastructure Attacks
The network infrastructure may also work in an inappropriate manner.
For instance, a Virtual Private Network (VPN) may misrepresent how it
carries the users' traffic, for example misrepresenting the countries
Arkko & Farrell Expires August 26, 2021 [Page 8]
Internet-Draft Internet Threat Model Evolution February 2021
in which they provide vantage points [Vpns]. A user's home network
equipment may also be malicous or compromised. For example, one
study [Home] reports on a 2011 attack that affected 4.5 million DSL
modems in Brazil. The absence of software update [RFC8240] has been
a major cause of these issues and rises to the level that considering
this as intentional behaviour by device vendors who have chosen this
path is warranted.
2.3.4. Untrustworthy Devices
Traditionally, there's been an implied trust in various parts of the
system - such as the user's own device, nodes inside a particular
network perimeter, or nodes under a single administrative control.
Client endpoint implementations were never fully trusted, but the
environments in which those endpoints exist are changing. Users may
not have as much control over their own devices as they used to, due
to manufacturer-controlled operating system installations and locked
device ecosystems. And within those ecosystems, even the
applications that are available tend to have privileges that users by
themselves might not desire those applications be granted, such as
excessive rights to media, location, and peripherals. There are also
designated efforts by various authorities to hack end-user devices as
a means of intercepting data about the user.
Examples of these issues are too many to list, for instance, so-
called "smart" televisions spying on their owners and one survey of
user attitudes [SmartTV].
There are similar issues with larger, networked systems. As these
systems evolve over time, they get used and connected in different
ways, run in virtual environments, and expanded for new functions.
Old assumptions and security mechanisms may no longer be applicable
in these new environments, leading to security vulnerabilities.
Even in a closed network with carefully managed components there may
be compromised components, as evidenced in the most extreme way by
the Stuxnet worm that operated in an airgapped network.
Every system runs large amount of software, and it is often not
practical or even possible to prevent compromised code even in a
high-security setting, let alone in commercial or private networks.
Installation media, physical ports, both open source and proprietary
programs, firmware, or even innocent-looking components on a circuit
board can be suspect [TinyChip]. In addition, complex underlying
computing platforms, such as modern CPUs with underlying security and
management tools are prone to problems. Analysis for the security of
many interesting real-world systems now commonly needs to include
Arkko & Farrell Expires August 26, 2021 [Page 9]
Internet-Draft Internet Threat Model Evolution February 2021
cross-component attacks, e.g., the use of car radios and other
externally communicating devices as part of attacks launched against
the control components such as brakes in a car [Savage].
Untrustworthy systems can also cause damage to other parties.
Examples of this range from attacks of badly constructed IoT devices
[DynDDoS] to large Internet services that become single points of
failure [I-D.arkko-arch-infrastructure-centralisation].
2.3.5. Tracking
One of the biggest threats to user privacy on the Web is ubiquitous
tracking. This is often done to support advertising based business
models.
While some people may be sanguine about this kind of tracking, others
consider this behaviour unwelcome, when or if they are informed that
it happens, [Attitude] though the evidence here seems somewhat harder
to interpret and many studies (that we have found to date) involve
small numbers of users. Historically, browsers have not made this
kind of tracking visible and have enabled it by default, though some
recent browser versions are starting to enable visibility and
blocking of some kinds of tracking. Browsers are also increasingly
imposing more stringent requirements on plug-ins for varied security
reasons.
Third party tracking
One form of tracking is by third parties. HTTP header fields (such
as cookies, [RFC6265]) are commonly used for such tracking, as are
structures within the content of HTTP responses such as links to 1x1
pixel images and (ab)use of Javascript APIs offered by browsers
[Tracking].
Whenever a resource is loaded from a server, that server can include
a cookie which will be sent back to the server on future loads. This
includes situations where the resource is loaded as a resource on a
page, such as an image or a JavaScript module. When loading a
resource, the server is aware of the top-level page that the resource
is used on, through the use of the Referer HTTP header [RFC7231].
those loads include a Referer header which contains the top-level
page from which that subresource is being loaded.
The combination of these features makes it possible to track a user
across the Web. The tracker convinces a number of content sites
("first parties") to include a resource from the tracker site. This
resource can perform some function such as displaying an
advertisement or providing analytics to the first party site. But
Arkko & Farrell Expires August 26, 2021 [Page 10]
Internet-Draft Internet Threat Model Evolution February 2021
the resource may also be simply a tracker. When the user visits one
of the content sites, the tracker receives both a Referer header and
the cookie. For an individual user with a particular browser, the
cookie is the same regardless of which site the tracker is on. This
allows the tracker to observe what pages within the set of content
sites the user visits. The resulting information is commonly used
for targeting advertisements, but it can also be used for other
purposes.
This capability itself constitutes a major threat to user privacy.
Additional techniques such as cookie syncing, identifier correlation,
and fingerprinting make the problem even worse
[I-D.wood-pearg-website-fingerprinting].
As a given tracker will not be on all sites, that tracker has
incomplete coverage. However, trackers often collude (a practice
called "cookie syncing") to combine the information from different
tracking cookies.
Sometimes trackers will be embedded on a site which collects a user
identifier, such as social media identity or an e-mail address. If
the site can inform the tracker of the identifier, that allows the
tracker to tie the identifier to the cookie.
While a browser may block cookies, fingerprinting browsers often
allows tracking the users. For instance, features such as User-Agent
string, plugin and font support, screen resolution, and timezone can
yield a fingerprint that is sometimes unique to a single user
[AmIUnique] and which persists beyond cookie scope and lifetime.
Even in cases where this fingerprint is not unique, the anonymity set
may be sufficiently small that, coupled with other data, this yields
a unique, per-user identifier. Fingerprinting of this type is more
prevalent on systems and platforms where data-set features are
flexible, such as desktops, where plugins are more commonly in use.
Fingerprinting prevention is an active research area; see [Boix2018]
for more information.
Other types of tracking linked to web tracking
Third party web tracking is not the only concern. An obvious
tracking danger exists also in popular ecosystems - such as social
media networks - that house a large part of many users' online
existence. There is no need for a third party to track the user's
browsing as all actions are performed within a single site, where
most messaging, viewing, and sharing activities happen.
Browsers themselves or services used by the browser can also become a
potential source of tracking users. For instance, the URL/search bar
Arkko & Farrell Expires August 26, 2021 [Page 11]
Internet-Draft Internet Threat Model Evolution February 2021
service may leak information about the user's actions to a search
provider via an "autocomplete" feature. [Leith2020]
Tracking through users' IP addresses or DNS queries is also a danger.
This may happen by directly observing the cleartext IP or DNS
traffic, though DNS tracking may be preventable via DNS protocols
that are secured end-to-end. But the DNS queries are also (by
definition) seen by the used DNS recursive resolver service, which
may accidentally or otherwise track the users' activities. This is
particularly problematic if a large number of users employ either a
commonly used ISP service or an Internet-based resolver service
[I-D.arkko-arch-infrastructure-centralisation]. In contrast, use of
a DNS recursive that sees little traffic could equally be used for
tracking. Similarly, other applications, such an mail or instant
messaging protocols, that can carry HTML content can be integrated
with web tracking. For instance, intentional tracking are also seen
many times per day by email users - in one study [Mailbug] the
authors estimated that 62% of leakage to third parties was
intentional, for example if leaked data included a hash of the
recipient email address.
Tracking happens through other systems besides the web, of course.
For instance, some mail user agents (MUAs) render HTML content by
default (with a subset not allowing that to be turned off, perhaps
particularly on mobile devices) and thus enable the same kind of
adversarial tracking seen on the web. Attempts at such intentional
tracking are also seen many times per day by email users - in one
study [Mailbug] the authors estimated that 62% of leakage to third
parties was intentional, for example if leaked data included a hash
of the recipient email address.
3. Principles
Based on the above issues, it is necessary to pay attention to the
following aspects:
o Security of devices, including the user's own devices.
o Security of data at rest, in various parts of the system.
o Tracking and identification of users and their devices.
o Role of intermediaries, and in particular information passing
through them.
These topics are discussed below. There are obviously many detailed
technical questions and approaches to tackling them. However, in
Arkko & Farrell Expires August 26, 2021 [Page 12]
Internet-Draft Internet Threat Model Evolution February 2021
this memo we wish to focus on higher level architectural principles
that might guide us in thinking about about the topics.
3.1. Trusting Devices
In general, this means that one cannot entirely trust even a closed
system where you picked all the components yourself, let alone
typical commercial, networked and Internet-connected systems.
PRINCIPLE: Consider all system components as potentially
untrustworthy, and consider the implications of their compromise.
There may also be ways to mitigate damages, should a compromise
occur.
3.2. Protecting Information
Data leaks have become the primary concern. Even trusted, well-
managed parties can be problematic, such as when large data stores
attract attempts to use that data in a manner that is not consistent
with the users' interests.
Mere encryption of communications is not sufficient to protect
information.
PRINCIPLE: Consider information passed to another party as a
publication to at least some number of entities.
This principle applies even if the communications that carry that
information are encrypted.
3.3. Tracking
Information leakage is particularly harmful in situations where the
information can be traced to an individual, such as is the case with
any information that users would consider private, be it about
messages to another users, browsing history, or even user's medical
information.
PRINCIPLE: Assume that every interaction with another party can
result in fingerprinting or identification of the user in
question.
In many cases there are readily available user identifiers in data
that is leaked, such as was the case with a recent medical
information leak in Finland [Vastaamo]. But even when such
identifiers are not present, in many communication methods, there is
ample opportunity for narrowing down which entity is connecting,
Arkko & Farrell Expires August 26, 2021 [Page 13]
Internet-Draft Internet Threat Model Evolution February 2021
through geolocation, fingerprinting, and correlation with other
information.
3.4. Role of End-to-End
[RFC1958] notes that "end-to-end functions can best be realised by
end-to-end protocols":
The basic argument is that, as a first principle, certain required
end-to-end functions can only be performed correctly by the end-
systems themselves. A specific case is that any network, however
carefully designed, will be subject to failures of transmission at
some statistically determined rate. The best way to cope with
this is to accept it, and give responsibility for the integrity of
communication to the end systems. Another specific case is end-
to-end security.
The "end-to-end argument" was originally described by Saltzer et al
[Saltzer]. They said:
The function in question can completely and correctly be
implemented only with the knowledge and help of the application
standing at the endpoints of the communication system. Therefore,
providing that questioned function as a feature of the
communication system itself is not possible.
These functional arguments align with other, practical arguments
about the evolution of the Internet under the end-to-end model. The
endpoints evolve quickly, often with simply having one party change
the necessary software on both ends. Whereas waiting for network
upgrades would involve potentially a large number of parties from
application owners to multiple network operators. The end-to-end
model supports permissionless innovation where new innovation can
flourish in the Internet without excessive wait for other parties to
act.
But the details matter. What is considered an endpoint? What
characteristics of Internet are we trying to optimize?
There is a significant difference between actual endpoints from a
user's interaction perspective (e.g., another user) and from a system
perspective (e.g., a third party relaying a message). Such
intermediaries can provide a useful service. As [I-D.thomson-tmi]
points out, networks themselves would not exist without
intermediaries that can forward communications to others.
PRINCIPLE: Limit the use of intermediaries, and what they can do.
Arkko & Farrell Expires August 26, 2021 [Page 14]
Internet-Draft Internet Threat Model Evolution February 2021
PRINCIPLE: Pass information only between the "real ends" of a
conversation, unless the information is necessary for a useful
function in an intermediary.
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 actually extends
beyond those components. For instance, just because an e-mail server
can read the contents of an e-mail message does not make it a
legitimate recipient of the e-mail.
This memo also proposes to focus on the "need to know" aspect in
systems. Information should not be disclosed, stored, or routed in
cleartext through parties that do not absolutely need to have that
information. This relates to the discussion in [I-D.thomson-tmi], in
that the valuable functions provided by intermediaries need to be
balanced against the information that they need to perform their
function. And, in a lot of cases unnecessary information is provided
to intermediaries, which leads to privacy and other problems.
4. Security Considerations
The entire memo covers the security considerations.
5. IANA Considerations
There are no IANA considerations in this work.
6. Informative References
[AbuseCases]
McDermott, J. and C. Fox, "Using abuse case models for
security requirements analysis", IEEE Annual Computer
Security Applications Conference (ACSAC'99),
https://www.acsac.org/1999/papers/wed-b-1030-john.pdf ,
1999.
[AmIUnique]
INRIA, ., "Am I Unique?", https://amiunique.org , 2020.
[Attitude]
"User Perceptions of Sharing, Advertising, and Tracking",
Symposium on Usable Privacy and Security (SOUPS),
https://www.usenix.org/conference/soups2015/proceedings/
presentation/chanchary , 2015.
Arkko & Farrell Expires August 26, 2021 [Page 15]
Internet-Draft Internet Threat Model Evolution February 2021
[avleak] Cox, J., "Leaked Documents Expose the Secretive Market for
Your Web Browsing Data",
https://www.vice.com/en_us/article/qjdkq7/
avast-antivirus-sells-user-browsing-data-investigation ,
2020.
[Bloatware]
Gamba, G., Rashed, M., Razaghpanah, A., Tapiado, J., and
N. Vallina, "An Analysis of Pre-installed Android
Software", arXiv preprint arXiv:1905.02713 (2019) , 2019.
[Boix2018]
Gomez-Boix, A., Laperdrix, P., and B. Baudry, "Hiding in
the crowd: an analysis of the effectiveness of browser
fingerprinting at large scale", Proceedings of the 2018
world wide web conference , 2018.
[Cambridge]
Isaak, J. and M. Hanna, "User Data Privacy: Facebook,
Cambridge Analytica, and Privacy Protection", Computer
51.8 (2018): 56-59, https://ieeexplore.ieee.org/stamp/
stamp.jsp?arnumber=8436400 , 2018.
[Curated] Hammad, M., Garcia, J., and S. MaleK, "A large-scale
empirical study on the effects of code obfuscations on
Android apps and anti-malware products", ACM International
Conference on Software Engineering 2018,
https://www.ics.uci.edu/~seal/
publications/2018ICSE_Hammad.pdf , 2018.
[DynDDoS] York, K., "Dyn's Statement on the 10/21/2016 DNS DDoS
Attack", Company statement: https://dyn.com/blog/
dyn-statement-on-10212016-ddos-attack/ , 2016.
[GDPRAccess]
EU, ., "Right of access by the data subject", Article 15,
GDPR, https://gdpr-info.eu/art-15-gdpr/ , n.d..
[Home] Nthala, N. and I. Flechais, "Rethinking home network
security", European Workshop on Usable Security
(EuroUSEC), https://ora.ox.ac.uk/objects/
uuid:e2460f50-579b-451b-b14e-b7be2decc3e1/download_file?sa
fe_filename=bare_conf_EuroUSEC2018.pdf&file_format=applica
tion%2Fpdf&type_of_work=Conference+item , 2018.
Arkko & Farrell Expires August 26, 2021 [Page 16]
Internet-Draft Internet Threat Model Evolution February 2021
[I-D.arkko-arch-dedr-report]
Arkko, J. and T. Hardie, "Report from the IAB workshop on
Design Expectations vs. Deployment Reality in Protocol
Development", draft-arkko-arch-dedr-report-00 (work in
progress), November 2019.
[I-D.arkko-arch-infrastructure-centralisation]
Arkko, J., "Centralised Architectures in Internet
Infrastructure", draft-arkko-arch-infrastructure-
centralisation-00 (work in progress), November 2019.
[I-D.arkko-arch-internet-threat-model]
Arkko, J., "Changes in the Internet Threat Model", draft-
arkko-arch-internet-threat-model-01 (work in progress),
July 2019.
[I-D.arkko-farrell-arch-model-t]
Arkko, J. and S. Farrell, "Challenges and Changes in the
Internet Threat Model", draft-arkko-farrell-arch-model-
t-04 (work in progress), July 2020.
[I-D.farrell-etm]
Farrell, S., "We're gonna need a bigger threat model",
draft-farrell-etm-03 (work in progress), July 2019.
[I-D.ietf-httpbis-expect-ct]
estark@google.com, e., "Expect-CT Extension for HTTP",
draft-ietf-httpbis-expect-ct-08 (work in progress),
December 2018.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-34 (work
in progress), January 2021.
[I-D.ietf-tls-esni]
Rescorla, E., Oku, K., Sullivan, N., and C. Wood, "TLS
Encrypted Client Hello", draft-ietf-tls-esni-09 (work in
progress), December 2020.
[I-D.lazanski-smart-users-internet]
Lazanski, D., "An Internet for Users Again", draft-
lazanski-smart-users-internet-00 (work in progress), July
2019.
Arkko & Farrell Expires August 26, 2021 [Page 17]
Internet-Draft Internet Threat Model Evolution February 2021
[I-D.thomson-tmi]
Thomson, M., "Principles for the Involvement of
Intermediaries in Internet Protocols", draft-thomson-
tmi-01 (work in progress), January 2021.
[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.
[Kocher2019]
Kocher, P., Horn, J., Fogh, A., Genkin, D., Gruss, D.,
Haas, W., Hamburg, M., Lipp, M., Mangard, S., Prescher,
T., Schwarz, M., and Y. Yarom, "Spectre Attacks:
Exploiting Speculative Execution", 40th IEEE Symposium on
Security and Privacy (S&P'19) , 2019.
[Leith2020]
Leith, D., "Web Browser Privacy: What Do Browsers Say When
They Phone Home?", In submission,
https://www.scss.tcd.ie/Doug.Leith/pubs/
browser_privacy.pdf , March 2020.
[Lipp2018]
Lipp, M., Schwarz, M., Gruss, D., Prescher, T., Haas, W.,
Fogh, A., Horn, J., Mangard, S., Kocher, P., Genkin, D.,
Yarom, Y., and M. Hamburg, "Meltdown: Reading Kernel
Memory from User Space", 27th USENIX Security Symposium
(USENIX Security 18) , 2018.
[Mailbug] Englehardt, S., Han, J., and A. Narayanan, "I never signed
up for this! Privacy implications of email tracking",
Proceedings on Privacy Enhancing Technologies 2018.1
(2018): 109-126, https://www.degruyter.com/downloadpdf/j/
popets.2018.2018.issue-1/popets-2018-0006/
popets-2018-0006.pdf , 2018.
[MeltdownAndSpectre]
CISA, ., "Meltdown and Spectre Side-Channel Vulnerability
Guidance", Alert (TA18-004A),
https://www.us-cert.gov/ncas/alerts/TA18-004A , 2018.
[Passwords]
com, haveibeenpwned., "Pwned Passwords", Website
https://haveibeenpwned.com/Passwords , 2019.
Arkko & Farrell Expires August 26, 2021 [Page 18]
Internet-Draft Internet Threat Model Evolution February 2021
[RFC1958] Carpenter, B., Ed., "Architectural Principles of the
Internet", RFC 1958, DOI 10.17487/RFC1958, June 1996,
<https://www.rfc-editor.org/info/rfc1958>.
[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>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.
[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797,
DOI 10.17487/RFC6797, November 2012,
<https://www.rfc-editor.org/info/rfc6797>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[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>.
[RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
2015, <https://www.rfc-editor.org/info/rfc7469>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC7817] Melnikov, A., "Updated Transport Layer Security (TLS)
Server Identity Check Procedure for Email-Related
Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016,
<https://www.rfc-editor.org/info/rfc7817>.
[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>.
Arkko & Farrell Expires August 26, 2021 [Page 19]
Internet-Draft Internet Threat Model Evolution February 2021
[RFC8240] Tschofenig, H. and S. Farrell, "Report from the Internet
of Things Software Update (IoTSU) Workshop 2016",
RFC 8240, DOI 10.17487/RFC8240, September 2017,
<https://www.rfc-editor.org/info/rfc8240>.
[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>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.
[Saltzer] Saltzer, J., Reed, D., and D. Clark, "End-To-End Arguments
in System Design", ACM TOCS, Vol 2, Number 4, pp 277-288 ,
November 1984.
[Savage] Savage, S., "Modern Automotive Vulnerabilities: Causes,
Disclosures, and Outcomes", USENIX , 2016.
[SmartTV] Malkin, N., Bernd, J., Johnson, M., and S. Egelman, "What
Can't Data Be Used For? Privacy Expectations about Smart
TVs in the U.S.", European Workshop on Usable Security
(Euro USEC), https://www.ndss-symposium.org/wp-
content/uploads/2018/06/
eurousec2018_16_Malkin_paper.pdf" , 2018.
[Sybil] Viswanath, B., Post, A., Gummadi, K., and A. Mislove, "An
analysis of social network-based sybil defenses", ACM
SIGCOMM Computer Communication Review 41(4), 363-374,
https://conferences.sigcomm.org/sigcomm/2010/papers/
sigcomm/p363.pdf , 2011.
[TargetAttack]
Osborne, C., "How hackers stole millions of credit card
records from Target", ZDNET,
https://www.zdnet.com/article/how-hackers-stole-millions-
of-credit-card-records-from-target/ , 2014.
Arkko & Farrell Expires August 26, 2021 [Page 20]
Internet-Draft Internet Threat Model Evolution February 2021
[TinyChip]
Robertson, J. and M. Riley, "The Big Hack: How China Used
a Tiny Chip to Infiltrate U.S. Companies",
https://www.bloomberg.com/news/features/2018-10-04/the-
big-hack-how-china-used-a-tiny-chip-to-infiltrate-america-
s-top-companies , October 2018.
[Toys] Chu, G., Apthorpe, N., and N. Feamster, "Security and
Privacy Analyses of Internet of Things Childrens' Toys",
IEEE Internet of Things Journal 6.1 (2019): 978-985,
https://arxiv.org/pdf/1805.02751.pdf , 2019.
[Tracking]
Ermakova, T., Fabian, B., Bender, B., and K. Klimek, "Web
Tracking-A Literature Review on the State of Research",
Proceedings of the 51st Hawaii International Conference on
System Sciences, https://scholarspace.manoa.hawaii.edu/
bitstream/10125/50485/paper0598.pdf , 2018.
[Troll] Stewart, L., Arif, A., and K. Starbird, "Examining trolls
and polarization with a retweet network", ACM Workshop on
Misinformation and Misbehavior Mining on the Web,
https://faculty.washington.edu/kstarbi/
examining-trolls-polarization.pdf , 2018.
[Unread] Obar, J. and A. Oeldorf, "The biggest lie on the
internet{:} Ignoring the privacy policies and terms of
service policies of social networking services",
Information, Communication and Society (2018): 1-20 ,
2018.
[Vastaamo]
Redcross Finland, ., "Read this if your personal data was
leaked in the Vastaamo data system break-in",
https://www.redcross.fi/news/20201029/read-if-your-
personal-data-was-leaked-vastaamo-data-system-break ,
October 2020.
[Vpns] Khan, M., DeBlasio, J., Voelker, G., Snoeren, A., Kanich,
C., and N. Vallina, "An empirical analysis of the
commercial VPN ecosystem", ACM Internet Measurement
Conference 2018 (pp. 443-456),
https://eprints.networks.imdea.org/1886/1/
imc18-final198.pdf , 2018.
Arkko & Farrell Expires August 26, 2021 [Page 21]
Internet-Draft Internet Threat Model Evolution February 2021
Appendix A. Contributors
Eric Rescorla and Chris Wood provided much of the text in
Section 2.3.5. Martin Thomson's excellent document [I-D.thomson-tmi]
also inspired some of the work in Section 3.
Appendix B. Acknowledgements
The authors would like to thank the IAB:
Alissa Cooper, Wes Hardaker, Ted Hardie, Christian Huitema, Zhenbin
Li, Erik Nordmark, Mark Nottingham, Melinda Shore, Jeff Tantsura,
Martin Thomson, Brian Trammel, Mirja Kuhlewind, and Colin Perkins.
The authors would also like to thank the participants of the IETF
SAAG meeting where this topic was discussed:
Harald Alvestrand, Roman Danyliw, Daniel Kahn Gilmore, Wes Hardaker,
Bret Jordan, Ben Kaduk, Dominique Lazanski, Eliot Lear, Lawrence
Lundblade, Kathleen Moriarty, Kirsty Paine, Eric Rescorla, Ali
Rezaki, Mohit Sethi, Ben Schwartz, Dave Thaler, Paul Turner, David
Waltemire, and Jeffrey Yaskin.
The authors would also like to thank the participants of the IAB 2019
DEDR workshop:
Tuomas Aura, Vittorio Bertola, Carsten Bormann, Stephane Bortzmeyer,
Alissa Cooper, Hannu Flinck, Carl Gahnberg, Phillip Hallam-Baker, Ted
Hardie, Paul Hoffman, Christian Huitema, Geoff Huston, Konstantinos
Komaitis, Mirja Kuhlewind, Dirk Kutscher, Zhenbin Li, Julien
Maisonneuve, John Mattson, Moritz Muller, Joerg Ott, Lucas Pardue,
Jim Reid, Jan-Frederik Rieckers, Mohit Sethi, Melinda Shore, Jonne
Soininen, Andrew Sullivan, and Brian Trammell.
The authors would also like to thank the participants of the November
2016 meeting at the IETF:
Carsten Bormann, Randy Bush, Tommy C, Roman Danyliw, Ted Hardie,
Christian Huitema, Ben Kaduk, Dirk Kutscher, Dominique Lazanski, Eric
Rescorla, Ali Rezaki, Mohit Sethi, Melinda Shore, Martin Thomson, and
Robin Wilton ... (missing many people... did we have minutes other
than the list of actions?) ...
Thanks for specific comments on this text to: Ronald van der Pol.
Finally, the authors would like to thank numerous other people for
insightful comments and discussions in this space.
Arkko & Farrell Expires August 26, 2021 [Page 22]
Internet-Draft Internet Threat Model Evolution February 2021
Authors' Addresses
Jari Arkko
Ericsson
Valitie 1B
Kauniainen
Finland
Email: jari.arkko@piuha.net
Stephen Farrell
Trinity College Dublin
College Green
Dublin
Ireland
Email: stephen.farrell@cs.tcd.ie
Arkko & Farrell Expires August 26, 2021 [Page 23]