draft-iab-privsec-confidentiality-mitigations-07.txt   draft-iab-privsec-confidentiality-mitigations-08.txt 
IAB T. Hardie, Ed. IAB T. Hardie, Ed.
Internet-Draft October 11, 2016 Internet-Draft October 27, 2016
Intended status: Informational Intended status: Informational
Expires: April 14, 2017 Expires: April 30, 2017
Confidentiality in the Face of Pervasive Surveillance Confidentiality in the Face of Pervasive Surveillance
draft-iab-privsec-confidentiality-mitigations-07 draft-iab-privsec-confidentiality-mitigations-08
Abstract Abstract
The IAB has published [RFC7624] in response to several revelations of The IAB has published [RFC7624] in response to several revelations of
pervasive attack on Internet communications. This document surveys pervasive attack on Internet communications. This document surveys
the most plausible mitigations to those threats currently available the most plausible mitigations to those threats currently available
to the designers of Internet protocols. to the designers of Internet protocols.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 14, 2017. This Internet-Draft will expire on April 30, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Available Mitigations . . . . . . . . . . . . . . . . . . . . 2 3. Available Mitigations . . . . . . . . . . . . . . . . . . . . 3
4. Interplay among Mechanisms . . . . . . . . . . . . . . . . . 8 3.1. Encryption . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 3.1.1. Forward Secrecy . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 3.1.2. Covert Channel Reduction . . . . . . . . . . . . . . 5
7. Contributors {Contributors} . . . . . . . . . . . . . . . . . 9 3.2. Auditing Authentication . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3. Metadata Minimization . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 9 3.3.1. Length Hiding . . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 9 3.4. Anonymization . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 3.5. End-to-End Protection . . . . . . . . . . . . . . . . . . 7
4. Interplay among Mechanisms . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Contributors {Contributors} . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
To ensure that the Internet can be trusted by users, it is necessary To ensure that the Internet can be trusted by users, it is necessary
for the Internet technical community to address the vulnerabilities for the Internet technical community to address the vulnerabilities
exploited in the attacks document in [RFC7258] and the threats exploited in the attacks document in [RFC7258] and the threats
described in [RFC7624]. The goal of this document is to describe described in [RFC7624]. The goal of this document is to describe
more precisely the mitigations available for those threats and to lay more precisely the mitigations available for those threats and to lay
out the interactions among them should they be deployed in out the interactions among them should they be deployed in
combination. combination.
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| | | | | |
| Static key exfiltration | Encryption with per-session state | | Static key exfiltration | Encryption with per-session state |
| | (PFS) | | | (PFS) |
| | | | | |
| Dynamic key exfiltration | Transparency, validation of end | | Dynamic key exfiltration | Transparency, validation of end |
| | systems | | | systems |
| | | | | |
| Content exfiltration | Object encryption, distributed systems | | Content exfiltration | Object encryption, distributed systems |
+--------------------------+----------------------------------------+ +--------------------------+----------------------------------------+
Figure 1: Table of Mitigations Table 1: Table of Mitigations
3.1. Encryption
The traditional mitigation to passive attack is to render content The traditional mitigation to passive attack is to render content
unintelligible to the attacker by applying encryption, for example, unintelligible to the attacker by applying encryption, for example,
by using TLS or IPsec [RFC5246][RFC4301]. Even without by using TLS or IPsec [RFC5246][RFC4301]. Even without
authentication, encryption will prevent a passive attacker from being authentication, encryption will prevent a passive attacker from being
able to read the encrypted content. Exploiting unauthenticated able to read the encrypted content. Exploiting unauthenticated
encryption requires an active attack (man in the middle); with encryption requires an active attack (man in the middle); with
authentication, a key exfiltration attack is required. For authentication, a key exfiltration attack is required. For
cryptographic systems providing forward secrecy, even exfiltration of cryptographic systems providing forward secrecy, even exfiltration of
long-term keys will not compromise data captured under session keys long-term keys will not compromise data captured under session keys
used before the exfiltration. used before the exfiltration.
3.1.1. Forward Secrecy
An encrypted, authenticated session is safe from content-monitoring
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].
3.1.2. Covert Channel Reduction
Dynamic key exfiltration cannot be prevented 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 into
products or if malware is injected later on.
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. 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 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.
3.2. Auditing Authentication
As with traditional, limited active attacks, a basic mitigation to
pervasive active attack is to enable the endpoints of a communication
to authenticate each other over the encrypted channel. However,
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]. Other systems may use external notaries to
detect certificate authority mismatch (e.g. Convergence
[Convergence]).
3.3. Metadata Minimization
The additional capabilities of a pervasive passive attacker, however, The additional capabilities of a pervasive passive attacker, however,
require some changes in how protocol designers evaluate what require some changes in how protocol designers evaluate what
information is encrypted. In addition to directly collecting information is encrypted. In addition to directly collecting
unencrypted data, a pervasive passive attacker can also make unencrypted data, a pervasive passive attacker can also make
inferences about the content of encrypted messages based on what is inferences about the content of encrypted messages based on what is
observable. For example, if a user typically visits a particular set observable. For example, if a user typically visits a particular set
of web sites, then a pervasive passive attacker observing all of the 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 user's behavior can track the user based on the hosts the user
communicates with, even if the user changes IP addresses, and even if communicates with, even if the user changes IP addresses, and even if
all of the connections are encrypted. all of the connections are encrypted.
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unencrypted in the protocol, and how that information might be unencrypted in the protocol, and how that information might be
correlated with other traffic. Some of the data left unencrypted may correlated with other traffic. Some of the data left unencrypted may
be considered "metadata" within the context of a single protocol, as be considered "metadata" within the context of a single protocol, as
it provides adjunct information used for delivery or display, rather it provides adjunct information used for delivery or display, rather
than the data directly created or consumed by protocol users. This than the data directly created or consumed by protocol users. This
does not mean it is not useful to attackers, however, and when this does not mean it is not useful to attackers, however, and when this
metadata is not protected by encryption it may leak substantial metadata is not protected by encryption it may leak substantial
amounts of information. Data minimization strategies should thus be amounts of information. Data minimization strategies should thus be
applied to any data left unencrypted, whether it be payload or applied to any data left unencrypted, whether it be payload or
metadata. Information that cannot be encrypted or omited should be metadata. Information that cannot be encrypted or omited should be
be dissociated from other information. For example, the TOR[TOR] be dissociated from other information. For example, the TOR overlay
overlay routing network anonymizes IP addresses by using multi-hop routing network [TOR] anonymizes IP addresses by using multi-hop
onion routing. onion routing.
As with traditional, limited active attacks, a basic mitigation to 3.3.1. Length Hiding
pervasive active attack is to enable the endpoints of a communication
to authenticate each other over the encrypted channel. However, One fundamental limitation of encryption is that it exposes the size
attackers that can mount pervasive active attacks can often subvert of the plaintext that protects. A passive attacker can use this to
the authorities on which authentication systems rely. Thus, in order obtain information about the plaintext [CLINIC]. Protocols that use
to make authentication systems more resilient to pervasive attack, it encryption can provide the ability to pad plaintext. This enables
is beneficial to monitor these authorities to detect misbehavior that control over the size of ciphertext by endpoints, which can be used
could enable active attack. For example, DANE and Certificate to reduce the information available to passive attackers.
Transparency both provide mechanisms for detecting when a CA has
issued a certificate for a domain name without the authorization of 3.4. Anonymization
the holder of that domain name [RFC6962][RFC6698]. Other systems may
use external notaries to detect certificate authority mismatch (e.g.
Convergence [Convergence]).
While encryption and authentication protect the security of While encryption and authentication protect the security of
individual sessions, these sessions may still leak information, such individual sessions, these sessions may still leak information, such
as IP addresses or server names, that a pervasive attacker can use to as IP addresses or server names, that a pervasive attacker can use to
correlate sessions and derive additional information about the correlate sessions and derive additional information about the
target. Thus, pervasive attack highlights the need for anonymization target. Thus, pervasive attack highlights the need for anonymization
technologies, which make correlation more difficult. Typical technologies, which make correlation more difficult. Typical
approaches to anonymization against traffic analysis include: approaches to anonymization against traffic analysis include:
o Aggregation: Routing sessions for many endpoints through a common o Aggregation: Routing sessions for many endpoints through a common
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example, a device has both a cellular and 802.11 interface, example, a device has both a cellular and 802.11 interface,
routing some traffic across the cellular network and other traffic routing some traffic across the cellular network and other traffic
over the 802.11 interface means that traffic analysis conducted over the 802.11 interface means that traffic analysis conducted
only with one network will be incomplete. Even if conducted in only with one network will be incomplete. Even if conducted in
both, it may be more difficult for the attacker to associate the both, it may be more difficult for the attacker to associate the
traffic in each network with the other. For this to be effective traffic in each network with the other. For this to be effective
as a mitigation, signalling protocols which gather and transmit as a mitigation, signalling protocols which gather and transmit
data about multiple interfaces (such as SIP) must be encrypted to data about multiple interfaces (such as SIP) must be encrypted to
avoid the information being used in cross-correlation. avoid the information being used in cross-correlation.
An encrypted, authenticated session is safe from content-monitoring 3.5. End-to-End Protection
attacks in which neither end collaborates with the attacker, but can
still be subverted by the endpoints. Ciphersuites used for HTTPS
based on RSA encryption, for example, allow an attacker with the
private key to 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 prevented 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 into
products or if malware is injected later on.
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. 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 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 Content exfiltration has some similarity to the dynamic exfiltration
case, in that nothing can prevent a collaborator from revealing what case, in that nothing can prevent a collaborator from revealing what
they know, and the mitigations against becoming an unwitting they know, and the mitigations against becoming an unwitting
collaborator apply. In this case, however, applications can limit collaborator apply. In this case, however, applications can limit
what the collaborator is able to reveal. For example, the S/MIME and what the collaborator is able to reveal. For example, the S/MIME and
PGP systems for secure email both deny intermediate servers access to PGP systems for secure email both deny intermediate servers access to
certain parts of the message [RFC5750][RFC2015]. Even if a server certain parts of the message [RFC5750][RFC2015]. Even if a server
were to provide an attacker with full access, the attacker would were to provide an attacker with full access, the attacker would
still not be able to read the protected parts of the message. still not be able to read the protected parts of the message.
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messages. These mail agents need to use hop-by-hop encryption and messages. These mail agents need to use hop-by-hop encryption and
traffic analysis mitigation to address this risk. traffic analysis mitigation to address this risk.
Mechanisms such as S/MIME and PGP are also known as "object-based" Mechanisms such as S/MIME and PGP are also known as "object-based"
security mechanisms (as opposed to "communications security" security mechanisms (as opposed to "communications security"
mechanisms), since they operate at the level of objects, rather than mechanisms), since they operate at the level of objects, rather than
communications sessions. Such secure object can be safely handled by communications sessions. Such secure object can be safely handled by
intermediaries in order to realize, for example, store and forward intermediaries in order to realize, for example, store and forward
messaging. In the examples above, the encrypted instant messages or messaging. In the examples above, the encrypted instant messages or
email messages would be the secure objects. Hop-to-hop security email messages would be the secure objects. Hop-to-hop security
mechanisms are generally difficult to retrofit onto a deployed mechanisms may be susceptible to downgrade attacks (e.g., STARTTLS-
system, and they make it difficult to determine the security posture secured SMTP has been downgraded by intermediate network nodes
of remote hops (e.g., STARTTLS-secured SMTP has been downgraded by [WaPo-STARTTLS]) in which case end-to-end mechanisms are advised.
intermediate network nodes [WaPo-STARTTLS]). End-to-end mechanisms
are advised.
The mitigations to the content exfiltration case regard participants The mitigations to the content exfiltration case regard participants
in the protocol as potential passive attackers themselves, and apply in the protocol as potential passive attackers themselves, and apply
the mitigations discussed above with regard to passive attack. the mitigations discussed above with regard to passive attack.
Information that is not necessary for these participants to fulfill Information that is not necessary for these participants to fulfill
their role in the protocol can be encrypted, and other information their role in the protocol can be encrypted, and other information
can be anonymized. can be anonymized.
The tools that we currently have have not generally been designed
with mitigation in mind, so they may need elaboration or adjustment
to be completely suitable. The next section examines one common
reason for such adjustment: managing the integration of one
mitigation with the environment in which it is deployed.
4. Interplay among Mechanisms 4. Interplay among Mechanisms
One of the key considerations in selecting mitigations is how to One of the key considerations in selecting mitigations is how to
manage the interplay among different mechanisms. Care must be taken manage the interplay among different mechanisms. Care must be taken
to avoid situations where a mitigation is rendered fruitless because to avoid situations where a mitigation is rendered fruitless because
of mechanisms which working at a different time scale or with a of mechanisms which working at a different time scale or with a
different aim. different aim.
The tools that we currently have have not generally been designed
with all of these mitigations in mind, so they may need elaboration
or adjustment to be completely suitable. Thus, managing the
integration of one mitigation with the environment in which it is
deployed is critical.
As an example, there is work in progress in IEEE 802 to standardize a As an example, there is work in progress in IEEE 802 to standardize a
method for the randomization of MAC Addresses. This work aims to method for the randomization of MAC Addresses. This work aims to
enable the MAC address to vary as the device connects to different enable the MAC address to vary as the device connects to different
networks, or connects at different times. In theory, the networks, or connects at different times. In theory, the
randomization will mitigate tracking by MAC address. However, the randomization will mitigate tracking by MAC address. However, the
randomization will be defeated if the adversary can link the randomization will be defeated if the adversary can link the
randomized MAC address to other identifiers such as the interface randomized MAC address to other identifiers such as the interface
identifier used in IPv6 addresses, the unique identifiers used in identifier used in IPv6 addresses, the unique identifiers used in
DHCP or DHCPv6, or unique identifiers used in various link-local DHCP or DHCPv6, or unique identifiers used in various link-local
discovery protocols. discovery protocols.
For mitigations which rely on aggregation to separate the origin of For mitigations which rely on aggregation to separate the origin of
traffic from its destination, care must be taken that the protocol traffic from its destination, care must be taken that the protocol
mechanics do not expose origin IP through secondary means. mechanics do not expose origin IP through secondary means.
[I-D.ietf-dnsop-edns-client-subnet] for example, documents a method [I-D.ietf-dnsop-edns-client-subnet] for example, documents a method
to carry the IP address or subnet of a querying party through a to carry the IP address or subnet of a querying party through a
recursive resolver to an authoritative resolver. Even with a recursive resolver to an authoritative resolver. Even with a
truncated IP address, this mechanism increases the likelihood that a truncated IP address, this mechanism increases the likelihood that a
pervasive monitor would be able to associate query traffic and pervasive monitor would be able to associate query traffic and
responses. If a client wished to ensure that its traffic did not responses.
expose this data, it would need to require that its stub resolver
emit any privacy-sensitive queries with a source NETMASK set to 0, as If a client wished to ensure that its traffic did not expose this
detailed in Section 5.1 of [I-D.ietf-dnsop-edns-client-subnet]. data, it would need to require that its stub resolver emit any
Given that setting this only occasionally might also be used a signal privacy-sensitive queries with a source NETMASK set to 0, as detailed
to observers, any client wishing to have any privacy sensitive in Section 5.1 of [I-D.ietf-dnsop-edns-client-subnet]. Given that
traffic would, in essence have to emit this for every query. While setting this only occasionally might also be used a signal to
this would succeed at providing the required privacy, given the observers, any client wishing to have any privacy sensitive traffic
mechanism proposed, it would also mean no split-DNS adjustments in would, in essence have to emit this for every query. While this
response would be possible for the privacy sensitive client. would succeed at providing the required privacy, given the mechanism
proposed, it would also mean no split-DNS adjustments in response
would be possible for the privacy sensitive client.
5. IANA Considerations 5. IANA Considerations
This memo makes no request of IANA. This memo makes no request of IANA.
6. Security Considerations 6. Security Considerations
This memorandum describes a series of mitigations to the attacks This memorandum describes a series of mitigations to the attacks
described in [RFC7258]. No such list could possibly be described in [RFC7258]. No such list could possibly be
comprehensive, nor is the attack therein described the only possible comprehensive, nor is the attack therein described the only possible
attack. attack.
7. Contributors {Contributors} 7. Contributors {Contributors}
This document is derived in part from the work initially done on the This document is derived in part from the work initially done on the
Perpass mailing list and at the STRINT workshop. Work from Brian Perpass mailing list and at the STRINT workshop. Work from Brian
Trammell, Bruce Schneier, Christian Huitema, Cullen Jennings, Daniel Trammell, Bruce Schneier, Christian Huitema, Cullen Jennings, Daniel
Borkmann, and Richard Barnes is incorporated here, as are ideas and Borkmann, Martin Thomson, and Richard Barnes is incorporated here, as
commentary from Jeff Hodges, Phillip Hallam-Baker, and Stephen are ideas and commentary from Jeff Hodges, Phillip Hallam-Baker, and
Farrell. Stephen Farrell.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 9, line 46 skipping to change at page 11, line 14
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann, Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A "Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624, Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015, DOI 10.17487/RFC7624, August 2015,
<http://www.rfc-editor.org/info/rfc7624>. <http://www.rfc-editor.org/info/rfc7624>.
8.2. Informative References 8.2. Informative References
[CLINIC] Miller, B., Huang, L., Joseph, A., and J. Tygar, "I Know
Why You Went to the Clinic: Risks and Realization of HTTPS
Traffic Analysis", March 2014.
[Convergence] [Convergence]
M Marlinspike, ., "Convergence Project", August 2011, M Marlinspike, ., "Convergence Project", August 2011,
<http://convergenc.io>. <http://convergenc.io>.
[I-D.ietf-dnsop-edns-client-subnet] [I-D.ietf-dnsop-edns-client-subnet]
Contavalli, C., Gaast, W., tale, t., and W. Kumari, Contavalli, C., Gaast, W., tale, t., and W. Kumari,
"Client Subnet in DNS Queries", draft-ietf-dnsop-edns- "Client Subnet in DNS Queries", draft-ietf-dnsop-edns-
client-subnet-08 (work in progress), April 2016. client-subnet-08 (work in progress), April 2016.
[RFC2015] Elkins, M., "MIME Security with Pretty Good Privacy [RFC2015] Elkins, M., "MIME Security with Pretty Good Privacy
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