Internet DRAFT - draft-barnes-pervasive-problem
draft-barnes-pervasive-problem
Network Working Group R. Barnes
Internet-Draft B. Schneier
Intended status: Informational C. Jennings
Expires: January 2, 2015 T. Hardie
July 01, 2014
Pervasive Attack: A Threat Model and Problem Statement
draft-barnes-pervasive-problem-01
Abstract
Documents published in 2013 have revealed several classes of
"pervasive" attack on Internet communications. In this document, we
review the main attacks that have been published, and develop a
threat model that describes these pervasive attacks. Based on this
threat model, we discuss the techniques that can be employed in
Internet protocol design to increase the protocols robustness to
pervasive attacks.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on January 2, 2015.
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described in the Simplified BSD License.
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1. Introduction
Starting in the June 2013, documents released to the press by Edward
Snowden have revealed several operations undertaken by intelligence
agencies to exploit Internet communications for intelligence
purposes. These attacks were largely based on protocol
vulnerabilities that were already known to exist. The attacks were
nonetheless striking in their pervasive nature, both in terms of the
amount of Internet communications targeted, and in terms of the
diversity of attack techniques employed.
To ensure that the Internet can be trusted by users, it is necessary
for the Internet technical community to address the vulnerabilities
exploited in these attacks [I-D.farrell-perpass-attack]. The goal of
this document is to describe more precisely the threats posed by
these pervasive attacks, and based on those threats, lay out the
problems that need to be solved in order to secure the Internet in
the face of those threats.
The remainder of this document is structured as follows. In
Section 3, we provide a brief summary of the attacks that have been
disclosed. Section 4 describes a threat model based on these
attacks, focusing on classes of attack that have not been a focus of
Internet engineering to date. Section 5 provides some high-level
guidance on how Internet protocols can defend against the threats
described here.
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2. Terminology
This document makes extensive use of standard security terminology;
see, for example, [RFC4949]. In addition, we use a few terms that
are specific to the attacks discussed here:
Pervasive Attack: An attack on Internet protocols that makes use of
access at a large number of points in the network, or otherwise
provides the attacker with access to a large amount of Internet
traffic.
Collaborator: An entity that is a legitimate participant in a
protocol, but who provides information about that interaction
(keys or data) to an attacker.
Key Exfiltration: The transmission of keying material for an
encrypted communication from a collaborator to an attacker
Content Exfiltration: The transmission of the content of a
communication from a collaborator to an attacker
Unwitting Collaborator: A collaborator that provides information to
the attacker not deliberately, but because the attacker has
exploited some technology used by the collaborator.
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3. Reported Instances of Large-Scale Attacks
Through recent revelations of sensitive documents in several media
outlets, the Internet community has been made aware of several
intelligence activities conducted by US and UK national intelligence
agencies, particularly the US National Security Agency (NSA) and the
UK Government Communications Headquarters (GCHQ). These documents
have revealed the methods that these agencies use to attack Internet
applications and obtain sensitive user information. Theses documents
suggest the following types of attacks have occurred:
o Large scale passive collection of Internet traffic
[pass1][pass2][pass3][pass4]. For example:
* The NSA XKEYSCORE system accesses data from multiple access
points and searches for "selectors" such as email addresses, at
the scale of tens of terabytes of data per day.
* The GCHQ Tempora system appears to have access to around 1,500
major cables passing through the UK.
* The NSA MUSCULAR program tapped cables between data centers
belonging to major service providers.
* Several programs appear perform wide-scale collection of
cookies in web traffic and location data from location-aware
portable devices such as smartphones.
o Decryption of TLS-protected Internet sessions [dec1][dec2][dec3].
For example, the NSA BULLRUN project appears to have had a budget
of around $250M per year to undermine encryption through multiple
approaches.
o Insertion of NSA devices as a man in the middle of Internet
transactions [TOR1][TOR2]. For example, the NSA QUANTUM system
appears to use several different techniques to hijack HTTP
connections, ranging from DNS response injection to HTTP 302
redirects.
o Direct acquisition of bulk data and metadata from service
providers [dir1][dir2][dir3]. For example, the NSA PRISM program
provides the agency with access to many types of user data (e.g.,
email, chat, VoIP).
o Use of implants (covert modifications or malware) to undermine
security and anonymity features [dec2][TOR1][TOR2]. For example:
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* NSA appears to use the QUANTUM man-in-the-middle system to
direct users to a FOXACID server, which delivers an implant
that makes the TOR anonymity service less effective.
* The BULLRUN program mentioned above includes the addition of
covert modifications to software as one means to undermine
encryption.
* There is also some suspicion that NSA modifications to the
DUAL_EC_DRBG random number generator were made to ensure that
keys generated using that generator could be predicted by NSA.
These suspicions have been reinforced by reports that RSA
Security was paid roughly $10M to make DUAL_EC_DRBG the default
in their products.
We use the term "pervasive attack" to collectively describe these
operations. The term "pervasive" is used because the attacks are
designed to gather as much data as possible and to apply selective
analysis on targets after the fact. This means that all, or nearly
all, Internet communications are targets for these attacks. To
achieve this scale, the attacks are physically pervasive; they affect
a large number of Internet communications. They are pervasive in
content, consuming and exploiting any information revealed by the
protocol. And they are pervasive in technology, exploiting many
different vulnerabilities in many different protocols.
It's important to note that although the attacks mentioned above were
executed by NSA and GCHQ, there are many other organizations that can
mount pervasive attacks. Because of the resources required to
achieve pervasive scale, pervasive attacks are most commonly
undertaken by nation-state actors. For example, the Chinese Internet
filtering system known as the "Great Firewall of China" uses several
techniques that are similar to the QUANTUM program, and which have a
high degree of pervasiveness with regard to the Internet in China.
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4. Threat Model
Pervasive surveillance aims to collect information across a large
number of Internet communications, analyzing the collected
communications to identify information of interest within individual
communications or implied by correlated communications. This
analysis sometimes benefits from decryption of encrypted
communications and deanonymization of anonymized communications. As
a result, these attackers desire both access to the bulk of Internet
traffic and to the keying material required to decrypt any traffic
which has been encrypted (though the presence of a communication and
the fact that it is encrypted may both be inputs to an analysis, even
if the attacker cannot decrypt the communication).
The attacks listed above highlight new avenues both for access to
traffic and for access to relevant encryption keys. They further
indicate that the scale of surveillance is sufficient to provide a
general capability to cross-correlate communications, a threat not
previously thought to be relevant at the scale of all Internet
communications.
4.1. Attacker Capabilities
+--------------------------+-------------------------------------+
| Attack Class | Capability |
+--------------------------+-------------------------------------+
| Passive | Capture data in transit |
| | |
| Active | Manipulate / inject data in transit |
| | |
| Static key exfiltration | Obtain key material once / rarely |
| | |
| Dynamic key exfiltration | Obtain per-session key material |
| | |
| Content exfiltration | Access data at rest |
+--------------------------+-------------------------------------+
Security analyses of Internet protocols commonly consider two classes
of attacker: Passive attackers, who can simply listen in on
communications as they transit the network, and "active attackers",
who can modify or delete packets in addition to simply collecting
them.
In the context of pervasive attack, these attacks take on an even
greater significance. In the past, these attackers are often assumed
to operate near the edge of the network, where attacks can be
simpler. For exmaple, in some LANs, it is simple for any node to
engage in passive listening to other nodes' traffic or inject packets
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to accomplish active attacks. In the pervasive attack case, however,
both passive and active attacks are undertaken closer to the core of
the network, greatly expanding the scope and capability of the
attacker.
A passive attacker with access to a large portion of the Internet can
analyze collected traffic to create a much more detailed view of user
behavior than an attacker that collects at a single point. Even the
usual claim that encryption defeats passive attackers is weakened,
since a pervasive passive attacker can examine correlations over
large numbers of sessions, e.g., pairing encrypted sessions with
unencrypted sessions from the same host. The reports on the NSA
XKEYSCORE system would make it an example of such an attacker.
A pervasive active attacker likewise has capabilities beyond those of
a localized active attacker. Active attacks are often limited by
network topology, for example by a requirement that the attacker be
able to see a targeted session as well as inject packets into it. A
pervasive active attacker with multiple accesses at core points of
the Internet is able to overcome these topological limitations and
apply attacks over a much broader scope. Being positioned in the
core of the network rather than the edge can also enable a pervasive
active attacker to reroute targeted traffic. Pervasive active
attackers can also benefit from pervasive passive collection to
identify vulnerable hosts.
While not directly related to pervasiveness, attackers that are in a
position to mount a pervasive active attack are also often in a
position to subvert authentication, the traditional response to
active attack. Authentication in the Internet is often achieved via
trusted third party authorities such as the Certificate Authorities
(CAs) that provide web sites with authentication credentials. An
attacker with sufficient resources for pervasive attack may also be
able to induce an authority to grant credentials for an identity of
the attacker's choosing. If the parties to a communication will
trust multiple authorities to certify a specific identity, this
attack may be mounted by suborning any one of the authorities (the
proverbial "weakest link"). Subversion of authorities in this way
can allow an active attack to succeed in spite of an authentication
check.
Beyond these two classes (active and passive), reports on the BULLRUN
effort to defeat encryption and the PRISM effort to obtain data from
service providers suggest three more classes of attack:
o Static key exfiltration
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o Dynamic key exfiltration
o Content exfiltration
These attacks all rely on a "collaborator" endpoint providing the
attacker with some information, either keys or data. These attacks
have not traditionally been considered in security analyses of
protocols, since they happen outside of the protocol.
The term "key exfiltration" refers to the transfer of keying material
for an encrypted communication from the collaborator to the attacker.
By "static", we mean that the transfer of keys happens once, or
rarely, typically of a long-lived key. For example, this case would
cover a web site operator that provides the private key corresponding
to its HTTPS certificate to an intelligence agency.
"Dynamic" key exfiltration, by contrast, refers to attacks in which
the collaborator delivers keying material to the attacker frequently,
e.g., on a per-session basis. This does not necessarily imply
frequent communications with the attacker; the transfer of keying
material may be virtual. For example, if an endpoint were modified
in such a way that the attacker could predict the state of its
psuedorandom number generator, then the attacker would be able to
derive per-session keys even without per-session communications.
Finally, content exfiltration is the attack in which the collaborator
simply provides the attacker with the desired data or metadata.
Unlike the key exfiltration cases, this attack does not require the
attacker to capture the desired data as it flows through the network.
The risk is to data at rest as opposed to data in transit. This
increases the scope of data that the attacker can obtain, since the
attacker can access historical data - the attacker does not have to
be listening at the time the communication happens.
Exfiltration attacks can be accomplished via attacks against one of
the parties to a communication, i.e., by the attacker stealing the
keys or content rather than the party providing them willingly. In
these cases, the party may not be aware that they are collaborating,
at least at a human level. Rather, the subverted technical assets
are "collaborating" with the attacker (by providing keys/content)
without their owner's knowledge or consent.
Any party that has access to encryption keys or unencrypted data can
be a collaborator. While collaborators are typically the endpoints
of a communication (with encryption securing the links),
intermediaries in an unencrypted communication can also facilitate
content exfiltration attacks as collaborators by providing the
attacker access to those communications. For example, documents
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describing the NSA PRISM program claim that NSA is able to access
user data directly from servers, where it was stored unencrypted. In
these cases, the operator of the server would be a collaborator
(wittingly or unwittingly). By contrast, in the NSA MUSCULAR
program, a set of collaborators enabled attackers to access the
cables connecting data centers used by service providers such as
Google and Yahoo. Because communications among these data centers
were not encrypted, the collaboration by an intermediate entity
allowed NSA to collect unencrypted user data.
4.2. Attacker Costs
+--------------------------+-----------------------------------+
| Attack Class | Cost / Risk to Attacker |
+--------------------------+-----------------------------------+
| Passive | Passive data access |
| | |
| Active | Active data access + processing |
| | |
| Static key exfiltration | One-time interaction |
| | |
| Dynamic key exfiltration | Ongoing interaction / code change |
| | |
| Content exfiltration | Ongoing, bulk interaction |
+--------------------------+-----------------------------------+
In order to realize an attack of each of the types discussed above,
the attacker has to incur certain costs and undertake certain risks.
These costs differ by attack, and can be helpful in guiding response
to pervasive attack.
Depending on the attack, the attacker may be exposed to several types
of risk, ranging from simply losing access to arrest or prosecution.
In order for any of these negative consequences to happen, however,
the attacker must first be discovered and identified. So the primary
risk we focus on here is the risk of discovery and attribution.
A passive attack is the simplest attack to mount in some ways. The
base requirement is that the attacker obtain physical access to a
communications medium and extract communications from it. For
example, the attacker might tap a fiber-optic cable, acquire a mirror
port on a switch, or listen to a wireless signal. The need for these
taps to have physical access to a link exposes the attacker to the
risk that the taps will be discovered. For example, a fiber tap or
mirror port might be discovered by network operators noticing
increased attenuation in the fiber or a change in switch
configuration. Of course, passive attacks may be accomplished with
the cooperation of the network operator, in which case there is a
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risk that the attacker's interactions with the network operator will
be exposed.
In many ways, the costs and risks for an active attack are similar to
those for a passive attack, with a few additions. An active attacker
requires more robust network access than a passive attacker, since
for example they will often need to transmit data as well as
receiving it. In the wireless example above, the attacker would need
to act as an transmitter as well as receiver, greatly increasing the
probability the attacker will be discovered (e.g., using direction-
finding technology). Active attacks are also much more observable at
higher layers of the network. For example, an active attacker that
attempts to use a mis-issued certificate could be detected via
Certificate Transparency [RFC6962].
In terms of raw implementation complexity, passive attacks require
only enough processing to extract information from the network and
store it. Active attacks, by contrast, often depend on winning race
conditions to inject pakets into active connections. So active
attacks in the core of the network require processing hardware to
that can operate at line speed (roughly 100Gbps to 1Tbps in the core)
to identify opportunities for attack and insert attack traffic in a
high-volume traffic.
Key exfiltration attacks rely on passive attack for access to
encrypted data, with the collaborator providing keys to decrypt the
data. So the attacker undertakes the cost and risk of a passive
attack, as well as additional risk of discovery via the interactions
that the attacker has with the collaborator.
In this sense, static exfiltration has a lower risk profile than
dynamic. In the static case, the attacker need only interact with
the collaborator a small number of times, possibly only once, say to
exchange a private key. In the dynamic case, the attacker must have
continuing interactions with the collaborator. As noted above these
interactions may real, such as in-person meetings, or virtual, such
as software modifications that render keys available to the attacker.
Both of these types of interactions introduce a risk that they will
be discovered, e.g., by employees of the collaborator organization
noticing suspicious meetings or suspicious code changes.
Content exfiltration has a similar risk profile to dynamic key
exfiltration. In a content exfiltration attack, the attacker saves
the cost and risk of conducting a passive attack. The risk of
discovery through interactions with the collaborator, however, is
still present, and may be higher. The content of a communication is
obviously larger than the key used to encrypt it, often by several
orders of magnitude. So in the content exfiltration case, the
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interactions between the collaborator and the attacker need to be
much higher-bandwidth than in the key exfiltration cases, with a
corresponding increase in the risk that this high-bandwidth channel
will be discovered.
It should also be noted that in these latter three exfiltration
cases, the collaborator also undertakes a risk that his collaboration
with the attacker will be discovered. Thus the attacker may have to
incur additional cost in order to convince the collaborator to
participate in the attack. Likewise, the scope of these attacks is
limited to case where the attacker can convince a collaborator to
participate. If the attacker is a national government, for example,
it may be able to compel participation within its borders, but have a
much more difficult time recruiting foreign collaborators.
As noted above, the "collaborator" in an exfiltration attack can be
unwitting; the attacker can steal keys or data to enable the attack.
In some ways, the risks of this approach are similar to the case of
an active collaborator. In the static case, the attacker needs to
steal information from the collaborator once; in the dynamic case,
the attacker needs to continued presence inside the collaborators
systems. The main difference is that the risk in this case is of
automated discovery (e.g., by intrusion detection systems) rather
than discovery by humans.
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5. Responding to Pervasive Attack
Given this threat model, how should the Internet technical community
respond to pervasive attack?
The cost and risk considerations discussed above can provide a guide
to response. Namely, responses to passive attack should close off
avenues for attack that are safe, scalable, and cheap, forcing the
attacker to mount attacks that expose it to higher cost and risk.
In this section, we discuss a collection of high-level approaches to
mitigating pervasive attacks. These approaches are not meant to be
exhaustive, but rather to provide general guidance to protocol
designers in creating protocols that are resistant to pervasive
attack.
+--------------------------+----------------------------------------+
| Attack Class | High-level mitigations |
+--------------------------+----------------------------------------+
| Passive | Encryption, anonymization |
| | |
| Active | Authentication, monitoring |
| | |
| Static key exfiltration | Encryption with per-session state |
| | (PFS) |
| | |
| Dynamic key exfiltration | Transparency, validation of end |
| | systems |
| | |
| Content exfiltration | Object encryption, distributed systems |
+--------------------------+----------------------------------------+
The traditional mitigation to passive attack is to render content
unintelligible to the attacker by applying encryption, for example,
by using TLS or IPsec [RFC5246][RFC4301]. Even without
authentication, encryption will prevent a passive attacker from being
able to read the encrypted content. Exploiting unauthenticated
encryption requires an active attack (man in the middle); with
authentication, a key exfiltration attack is required.
The additional capabilities of a pervasive passive attacker, however,
require some changes in how protocol designers evaluate what
information is encrypted. In addition to directly collecting
unencrypted data, a pervasive passive attacker can also make
inferences about the content of encrypted messages based on what is
observable. For example, if a user typically visits a particular set
of web sites, then a pervasive passive attacker observing all of the
user's behavior can track the user based on the hosts the user
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communicates with, even if the user changes IP addresses, and even if
all of the connections are encrypted.
Thus, in designing protocols to be resistant to pervasive passive
attacks, protocol designers should consider what information is left
unencrypted in the protocol, and how that information might be
correlated with other traffic. Information that cannot be encrypted
should be anonymized, i.e., it should be randomized so that it cannot
be correlated with other information. For example, the TOR overlay
routing network anonymizes IP addresses by using multi-hop onion
routing [TOR].
As with traditional, limited active attacks, the basic mitigation to
pervasive active attack is to enable the endpoints of a communication
to authenticate each other. However, as noted above, attackers that
can mount pervasive active attacks can often subvert the authorities
on which authentication systems rely. Thus, in order to make
authentication systems more resilient to pervasive attack, it is
beneficial to monitor these authorities to detect misbehavior that
could enable active attack. For example, DANE and Certificate
Transparency both provide mechanisms for detecting when a CA has
issued a certificate for a domain name without the authorization of
the holder of that domain name [RFC6962][RFC6698].
While encryption and authentication protect the security of
individual sessions, these sessions may still leak information, such
as IP addresses or server names, that a pervasive attacker can use to
correlate sessions and derive additional information about the
target. Thus, pervasive attack highlights the need for anonymization
technologies, which make correlation more difficult. Typical
approaches to anonymization include:
o Aggregation: Routing sessions for many endpoints through a common
mid-point (e.g., an HTTP proxy). Since the midpoint appears as
the end of the communication, individual endpoints cannot be
distinguished.
o Onion routing: Routing a session through several mid-points,
rather than directly end-to-end, with encryption that guarantees
that each node can only see the previous and next hops [TOR].
This ensures that the source and destination of a communication
are never revealed simultaneously.
o Multi-path: Routing different sessions via different paths (even
if they originate from the same endpoint). This reduces the
probability that the same attacker will be able to collect many
sessions.
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An encrypted, authenticated session is safe from attacks in which
neither end collaborates with the attacker, but can still be
subverted by the endpoints. The most common ciphersuites used for
HTTPS today, for example, are based on using RSA encryption in such a
way that if an attacker has the private key, the attacker can derive
the session keys from passive observation of a session. These
ciphersuites are thus vulnerable to a static key exfiltration attack
- if the attacker obtains the server's private key once, then they
can decrypt all past and future sessions for that server.
Static key exfiltration attacks are prevented by including ephemeral,
per-session secret information in the keys used for a session. Most
IETF security protocols include modes of operation that have this
property. These modes are known in the literature under the heading
"perfect forward secrecy" (PFS) because even if an adversary has all
of the secrets for one session, the next session will use new,
different secrets and the attacker will not be able to decrypt it.
The Internet Key Exchange (IKE) protocol used by IPsec supports PFS
by default [RFC4306], and TLS supports PFS via the use of specific
ciphersuites [RFC5246].
Dynamic key exfiltration cannot be prevent by protocol means. By
definition, any secrets that are used in the protocol will be
transmitted to the attacker and used to decrypt what the protocol
encrypts. Likewise, no technical means will stop a willing
collaborator from sharing keys with an attacker. However, this
attack model also covers "unwitting collaborators", whose technical
resources are collaborating with the attacker without their owners
knowledge. This could happen, for example, if flaws are built in
products or if malware is injected later on.
The best defense against becoming an unwitting collaborator is thus
to end systems are well-vetted and secure. Transparency is a major
tool in this process [secure]. Open source software is easier to
evaluate for potential flaws than proprietary software. Products
that conform to standards for cryptography and security protocols are
limited in the ways they can misbehave. And standards processes that
are open and transparent help ensure that the standards themselves do
not provide avenues for attack.
Standards can also define protocols that provide greater or lesser
opportunity for dynamic key exfiltration. Collaborators engaging in
key exfiltration through a standard protocol will need to use covert
channels in the protocol to leak information that can be used by the
attacker to recover the key. Such use of covert channels has been
demonstrated for SSL, TLS, and SSH [key-recovery]. Any protocol bits
that can be freely set by the collaborator can be used as a covert
channel, including, for example, TCP options or unencrypted traffic
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sent before a STARTTLS message in SMTP or XMPP. Protocol designers
should consider what covert channels their protocols expose, and how
those channels can be exploited to exfiltrate key information.
Content exfiltration has some similarity to the dynamic exfiltration
case, in that nothing can prevent a collaborator from revealing what
they know, and the mitigations against becoming an unwitting
collaborator apply. In this case, however, applications can limit
what the collaborator is able to reveal. For example, the S/MIME and
PGP systems for secure email both deny intermediate servers access to
certain parts of the message [RFC5750][RFC2015]. Even if a server
were to provide an attacker with full access, the attacker would
still not be able to read the protected parts of the message.
Mechanisms like S/MIME and PGP are often referred to as "end-to-end"
security mechanisms, as opposed to "hop-by-hop" or "end-to-middle"
mechanisms like the use of SMTP over TLS. These two different
mechanisms address different types of attackers: Hop-by-hop
mechanisms protect from attackers on the wire (passive or active),
while end-to-end mechansims protect against attackers within
intermediate nodes. Thus, neither of these mechanisms provides
complete protection by itself. For example:
o Two users messaging via Facebook over HTTPS are protected against
passive and active attackers in the network between the users and
Facebook. However, if Facebook is a collaborator in an
exfiltration attack, their communications can still be monitored.
They would need to encrypt their messages end-to-end in order to
protect themselves against this risk.
o Two users exchanging PGP-protected email have protected the
content of their exchange from network attackers and intermediate
servers, but the header information (e.g., To and From addresses)
is unnecessarily exposed to passive and active attackers that can
see communications among the mail agents handling the email
messages. These mail agents need to use hop-by-hop encryption to
address this risk.
Mechanisms such as S/MIME and PGP are also known as "object-based"
security mechanisms (as opposed to "communications security"
mechanisms), since they operate at the level of objects, rather than
communications sessions. Such secure object can be safely handled by
intermediaries in order to realize, for example, store and forward
messaging. In the examples above, the encrypted instant messages or
email messages would be the secure objects.
The mitigations to the content exfiltration case are thus to regard
participants in the protocol as potential passive attackers
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themselves, and apply the mitigations discussed above with regard to
passive attack. Information that is not necessary for these
participants to fulfill their role in the protocol can be encrypted,
and other information can be anonymized.
In summary, many of the basic tools for mitigating pervasive attack
already exist. As Edward Snowden put it, "properly implemented
strong crypto systems are one of the few things you can rely on"
[snowden]. The task for the Internet community is to ensure that
applications are able to use the strong crypto systems we have
defined - for example, TLS with PFS ciphersuites - and that these
properly implemented. (And, one might add, turned on!) Some of this
work will require architectural changes to applications, e.g., in
order to limit the information that is exposed to servers. In many
other cases, however, the need is simply to make the best use we can
of the cryptographic tools we have.
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6. Acknowledgements
o Trammel for ideas around pervasive passive attack and mitigation
o Thaler for list of attacks and taxonomy
o Security ADs for starting and managing the perpass discussion
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7. TODO
o More thorough review of problem statement documents to ensure all
bases are covered
o Look at better alignment with draft-farrell-perpass-attack
o Better coverage of traffic analysis and mitigations
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8. Informative References
[pass1] The Guardian, "How the NSA is still harvesting your online
data", 2013, <http://www.theguardian.com/world/2013/jun/
27/nsa-online-metadata-collection>.
[pass2] The Guardian, "NSA's Prism surveillance program: how it
works and what it can do", 2013, <http://
www.theguardian.com/world/2013/jun/08/
nsa-prism-server-collection-facebook-google>.
[pass3] The Guardian, "XKeyscore: NSA tool collects 'nearly
everything a user does on the internet'", 2013, <http://
www.theguardian.com/world/2013/jul/31/
nsa-top-secret-program-online-data>.
[pass4] The Guardian, "How does GCHQ's internet surveillance
work?", n.d., <http://www.theguardian.com/uk/2013/jun/21/
how-does-gchq-internet-surveillance-work>.
[dec1] The New York Times, "N.S.A. Able to Foil Basic Safeguards
of Privacy on Web", 2013, <http://www.nytimes.com/2013/09/
06/us/nsa-foils-much-internet-encryption.html>.
[dec2] The Guardian, "Project Bullrun - classification guide to
the NSA's decryption program", 2013, <http://
www.theguardian.com/world/interactive/2013/sep/05/
nsa-project-bullrun-classification-guide>.
[dec3] The Guardian, "Revealed: how US and UK spy agencies defeat
internet privacy and security", 2013, <http://
www.theguardian.com/world/2013/sep/05/
nsa-gchq-encryption-codes-security>.
[TOR] The Tor Project, "TOR", 2013,
<https://www.torproject.org/>.
[TOR1] Schneier, B., "How the NSA Attacks Tor/Firefox Users With
QUANTUM and FOXACID", 2013, <https://www.schneier.com/
blog/archives/2013/10/how_the_nsa_att.html>.
[TOR2] The Guardian, "'Tor Stinks' presentation - read the full
document", 2013, <http://www.theguardian.com/world/
interactive/2013/oct/04/
tor-stinks-nsa-presentation-document>.
[dir1] The Guardian, "NSA collecting phone records of millions of
Verizon customers daily", 2013, <http://
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www.theguardian.com/world/2013/jun/06/
nsa-phone-records-verizon-court-order>.
[dir2] The Guardian, "NSA Prism program taps in to user data of
Apple, Google and others", 2013, <http://
www.theguardian.com/world/2013/jun/06/
us-tech-giants-nsa-data>.
[dir3] The Guardian, "Sigint - how the NSA collaborates with
technology companies", 2013, <http://www.theguardian.com/
world/interactive/2013/sep/05/
sigint-nsa-collaborates-technology-companies>.
[secure] Schneier, B., "NSA surveillance: A guide to staying
secure", 2013, <http://www.theguardian.com/world/2013/sep/
05/nsa-how-to-remain-secure-surveillance>.
[snowden] Technology Review, "NSA Leak Leaves Crypto-Math Intact but
Highlights Known Workarounds", 2013, <http://
www.technologyreview.com/news/519171/
nsa-leak-leaves-crypto-math-intact-but-highlights-known-
workarounds/>.
[key-recovery]
Golle, P., "The Design and Implementation of Protocol-
Based Hidden Key Recovery", 2003,
<http://crypto.stanford.edu/~pgolle/papers/escrow.pdf>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, June 2013.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC5750] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
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Mail Extensions (S/MIME) Version 3.2 Certificate
Handling", RFC 5750, January 2010.
[RFC2015] Elkins, M., "MIME Security with Pretty Good Privacy
(PGP)", RFC 2015, October 1996.
[I-D.farrell-perpass-attack]
Farrell, S. and H. Tschofenig, "Pervasive Monitoring is an
Attack", draft-farrell-perpass-attack-06 (work in
progress), February 2014.
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Authors' Addresses
Richard Barnes
Email: rlb@ipv.sx
Bruce Schneier
Email: schneier@schneier.com
Cullen Jennings
Email: fluffy@cisco.com
Ted Hardie
Email: ted.ietf@gmail.com
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