| Rfc | 8404 |
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| Title | Effects of Pervasive Encryption on Operators |
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| Author | K. Moriarty, Ed., A.
Morton, Ed. |
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| Date | July 2018 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | INFORMATIONAL |
|---|
|
Internet Engineering Task Force (IETF) K. Moriarty, Ed.
Request for Comments: 8404 Dell EMC
Category: Informational A. Morton, Ed.
ISSN: 2070-1721 AT&T Labs
July 2018
Effects of Pervasive Encryption on Operators
Abstract
Pervasive monitoring attacks on the privacy of Internet users are of
serious concern to both user and operator communities. RFC 7258
discusses the critical need to protect users' privacy when developing
IETF specifications and also recognizes that making networks
unmanageable to mitigate pervasive monitoring is not an acceptable
outcome: an appropriate balance is needed. This document discusses
current security and network operations as well as management
practices that may be impacted by the shift to increased use of
encryption to help guide protocol development in support of
manageable and secure networks.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It has been approved for publication by the Internet
Engineering Steering Group (IESG). Not all documents approved by the
IESG are candidates for any level of Internet Standard; see Section 2
of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8404.
Copyright Notice
Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Additional Background on Encryption Changes . . . . . . . 5
1.2. Examples of Attempts to Preserve Functions . . . . . . . 7
2. Network Service Provider Monitoring Practices . . . . . . . . 8
2.1. Passive Monitoring . . . . . . . . . . . . . . . . . . . 8
2.1.1. Traffic Surveys . . . . . . . . . . . . . . . . . . . 8
2.1.2. Troubleshooting . . . . . . . . . . . . . . . . . . . 9
2.1.3. Traffic-Analysis Fingerprinting . . . . . . . . . . . 11
2.2. Traffic Optimization and Management . . . . . . . . . . . 12
2.2.1. Load Balancers . . . . . . . . . . . . . . . . . . . 12
2.2.2. Differential Treatment Based on Deep Packet
Inspection (DPI) . . . . . . . . . . . . . . . . . . 14
2.2.3. Network-Congestion Management . . . . . . . . . . . . 16
2.2.4. Performance-Enhancing Proxies . . . . . . . . . . . . 16
2.2.5. Caching and Content Replication near the Network Edge 17
2.2.6. Content Compression . . . . . . . . . . . . . . . . . 18
2.2.7. Service Function Chaining . . . . . . . . . . . . . . 18
2.3. Content Filtering, Network Access, and Accounting . . . . 19
2.3.1. Content Filtering . . . . . . . . . . . . . . . . . . 19
2.3.2. Network Access and Data Usage . . . . . . . . . . . . 20
2.3.3. Application Layer Gateways (ALGs) . . . . . . . . . . 21
2.3.4. HTTP Header Insertion . . . . . . . . . . . . . . . . 22
3. Encryption in Hosting and Application SP Environments . . . . 23
3.1. Management-Access Security . . . . . . . . . . . . . . . 23
3.1.1. Monitoring Customer Access . . . . . . . . . . . . . 24
3.1.2. SP Content Monitoring of Applications . . . . . . . . 24
3.2. Hosted Applications . . . . . . . . . . . . . . . . . . . 26
3.2.1. Monitoring Managed Applications . . . . . . . . . . . 27
3.2.2. Mail Service Providers . . . . . . . . . . . . . . . 27
3.3. Data Storage . . . . . . . . . . . . . . . . . . . . . . 28
3.3.1. Object-Level Encryption . . . . . . . . . . . . . . . 28
3.3.2. Disk Encryption, Data at Rest (DAR) . . . . . . . . . 29
3.3.3. Cross-Data-Center Replication Services . . . . . . . 29
4. Encryption for Enterprises . . . . . . . . . . . . . . . . . 30
4.1. Monitoring Practices of the Enterprise . . . . . . . . . 30
4.1.1. Security Monitoring in the Enterprise . . . . . . . . 31
4.1.2. Monitoring Application Performance in the Enterprise 32
4.1.3. Diagnostics and Troubleshooting for Enterprise
Networks . . . . . . . . . . . . . . . . . . . . . . 33
4.2. Techniques for Monitoring Internet-Session Traffic . . . 34
5. Security Monitoring for Specific Attack Types . . . . . . . . 36
5.1. Mail Abuse and Spam . . . . . . . . . . . . . . . . . . . 37
5.2. Denial of Service . . . . . . . . . . . . . . . . . . . . 37
5.3. Phishing . . . . . . . . . . . . . . . . . . . . . . . . 38
5.4. Botnets . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.5. Malware . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.6. Spoofed-Source IP Address Protection . . . . . . . . . . 39
5.7. Further Work . . . . . . . . . . . . . . . . . . . . . . 39
6. Application-Based Flow Information Visible to a Network . . . 40
6.1. IP Flow Information Export . . . . . . . . . . . . . . . 40
6.2. TLS Server Name Indication . . . . . . . . . . . . . . . 40
6.3. Application-Layer Protocol Negotiation (ALPN) . . . . . . 41
6.4. Content Length, Bitrate, and Pacing . . . . . . . . . . . 42
7. Effect of Encryption on the Evolution of Mobile Networks . . 42
8. Response to Increased Encryption and Looking Forward . . . . 43
9. Security Considerations . . . . . . . . . . . . . . . . . . . 43
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
11. Informative References . . . . . . . . . . . . . . . . . . . 44
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53
1. Introduction
In response to pervasive monitoring revelations and the IETF
consensus that pervasive monitoring is an attack [RFC7258], efforts
are underway to increase encryption of Internet traffic. Pervasive
monitoring is of serious concern to users, operators, and application
providers. RFC 7258 discusses the critical need to protect users'
privacy when developing IETF specifications and also recognizes that
making networks unmanageable to mitigate pervasive monitoring is not
an acceptable outcome; rather, an appropriate balance would emerge
over time.
This document describes practices currently used by network operators
to manage, operate, and secure their networks and how those practices
may be impacted by a shift to increased use of encryption. It
provides network operators' perspectives about the motivations and
objectives of those practices as well as effects anticipated by
operators as use of encryption increases. It is a summary of
concerns of the operational community as they transition to managing
networks with less visibility. This document does not endorse the
use of the practices described herein, nor does it aim to provide a
comprehensive treatment of the effects of current practices, some of
which have been considered controversial from a technical or business
perspectives or contradictory to previous IETF statements (e.g.,
[RFC1958], [RFC1984], and [RFC2804]). The following RFCs consider
the end-to-end (e2e) architectural principle to be a guiding
principle for the development of Internet protocols [RFC2775]
[RFC3724] [RFC7754].
This document aims to help IETF participants understand network
operators' perspectives about the impact of pervasive encryption,
both opportunistic and strong end-to-end encryption, on operational
practices. The goal is to help inform future protocol development to
ensure that operational impact is part of the conversation. Perhaps
new methods could be developed to accomplish some of the goals of
current practices despite changes in the extent to which cleartext
will be available to network operators (including methods that rely
on network endpoints where applicable). Discussion of current
practices and the potential future changes is provided as a
prerequisite to potential future cross-industry and cross-layer work
to support the ongoing evolution towards a functional Internet with
pervasive encryption.
Traditional network management, planning, security operations, and
performance optimization have been developed on the Internet where a
large majority of data traffic flows without encryption. While
unencrypted traffic has made information that aids operations and
troubleshooting at all layers accessible, it has also made pervasive
monitoring by unseen parties possible. With broad support and
increased awareness of the need to consider privacy in all aspects
across the Internet, it is important to catalog existing management,
operational, and security practices that have depended upon the
availability of cleartext to function and to explore if critical
operational practices can be met by less-invasive means.
This document refers to several different forms of Service Providers
(SPs). For example, network service providers (or network operators)
provide IP-packet transport primarily, though they may bundle other
services with packet transport. Alternatively, application service
providers primarily offer systems that participate as an endpoint in
communications with the application user and hosting service
providers lease computing, storage, and communications systems in
data centers. In practice, many companies perform two or more
service provider roles but may be historically associated with one.
This document includes a sampling of current practices and does not
attempt to describe every nuance. Some sections cover technologies
used over a broad spectrum of devices and use cases.
1.1. Additional Background on Encryption Changes
Pervasive encryption in this document refers to all types of session
encryption including Transport Layer Security (TLS), IP Security
(IPsec), TCPcrypt [TCPcrypt], QUIC [QUIC] (IETF's specification of
Google's QUIC), and others that are increasingly deployed. It is
well understood that session encryption helps to prevent both passive
and active attacks on transport protocols; more on pervasive
monitoring can be found in "Confidentiality in the Face of Pervasive
Surveillance: A Threat Model and Problem Statement" [RFC7624].
Active attacks have long been a motivation for increased encryption,
and preventing pervasive monitoring became a focus just a few years
ago. As such, the Internet Architecture Board (IAB) released a
statement advocating for increased use of encryption in November 2014
(see <https://www.iab.org/2014/11/14/iab-statement-on-internet-
confidentiality/>). Perspectives on encryption paradigms have
shifted over time to make ease of deployment a high priority and to
balance that against providing the maximum possible level of
security, regardless of deployment considerations.
One such shift is documented in Opportunistic Security (OS)
[RFC7435], which suggests that when use of authenticated encryption
is not possible, cleartext sessions should be upgraded to
unauthenticated session encryption, rather than no encryption. OS
encourages upgrading from cleartext but cannot require or guarantee
such upgrades. Once OS is used, it allows for an evolution to
authenticated encryption. These efforts are necessary to improve an
end user's expectation of privacy, making pervasive monitoring cost
prohibitive. With OS in use, active attacks are still possible on
unauthenticated sessions. OS has been implemented as NULL
Authentication with IPsec [RFC7619], and there are a number of
infrastructure use cases such as server-to-server encryption where
this mode is deployed. While OS is helpful in reducing pervasive
monitoring by increasing the cost to monitor, it is recognized that
risk profiles for some applications require authenticated and secure
session encryption as well prevention of active attacks. IPsec, and
other session encryption protocols, with authentication has many
useful applications, and usage has increased for infrastructure
applications such as for virtual private networks between data
centers. OS, as well as other protocol developments like the
Automated Certificate Management Environment (ACME), have increased
the usage of session encryption on the Internet.
Risk profiles vary and so do the types of session encryption
deployed. To understand the scope of changes in visibility, a few
examples are highlighted. Work continues to improve the
implementation, development, and configuration of TLS and DTLS
sessions to prevent active attacks used to monitor or intercept
session data. The changes from TLS 1.2 to 1.3 enhance the security
of TLS, while hiding more of the session negotiation and providing
less visibility on the wire. The Using TLS in Applications (UTA)
Working Group has been publishing documentation to improve the
security of TLS and DTLS sessions. They have documented the known
attack vectors in [RFC7457], have documented best practices for TLS
and DTLS in [RFC7525], and have other documents in development. The
recommendations from these documents were built upon for TLS 1.3 to
provide a more inherently secure end-to-end protocol.
In addition to encrypted website access (HTTP over TLS), there are
other well-deployed application-level transport encryption efforts
such as MTA-to-MTA (mail transfer agent) session encryption transport
for email (SMTP over TLS) and gateway-to-gateway for instant
messaging (the Extensible Messaging and Presence Protocol (XMPP) over
TLS). Although this does provide protection from transport-layer
attacks, the servers could be a point of vulnerability if user-to-
user encryption is not provided for these messaging protocols.
User-to-user content encryption schemes, such as S/MIME and Pretty
Good Privacy (PGP) for email and Off-the-Record (OTR) encryption for
XMPP are used by those interested in protecting their data as it
crosses intermediary servers, preventing transport-layer attacks by
providing an end-to-end solution. User-to-user schemes are under
review, and additional options will emerge to ease the configuration
requirements, making this type of option more accessible to
non-technical users interested in protecting their privacy.
Increased use of encryption, either opportunistic or authenticated,
at the transport, network, or application layer, impacts how networks
are operated, managed, and secured. In some cases, new methods to
operate, manage, and secure networks will evolve in response. In
other cases, currently available capabilities for monitoring or
troubleshooting networks could become unavailable. This document
lists a collection of functions currently employed by network
operators that may be impacted by the shift to increased use of
encryption. This document does not attempt to specify responses or
solutions to these impacts; it documents the current state.
1.2. Examples of Attempts to Preserve Functions
Following the Snowden [Snowden] revelations, application service
providers (Yahoo, Google, etc.) responded by encrypting traffic
between their data centers (IPsec) to prevent passive monitoring from
taking place unbeknownst to them. Infrastructure traffic carried
over the public Internet has been encrypted for some time; this
change for universal encryption was specific to their private
backbones. Large mail service providers also began to encrypt
session transport (TLS) to hosted mail services. This and other
increases in the use of encryption had the immediate effect of
providing confidentiality and integrity for protected data, but it
created a problem for some network-management functions. Operators
could no longer gain access to some session streams resulting in
actions by several to regain their operational practices that
previously depended on cleartext data sessions.
The Electronic Frontier Foundation (EFF) reported [EFF2014] several
network service providers using a downgrade attack to prevent the use
of SMTP over TLS by breaking STARTTLS (Section 3.2 of [RFC7525]),
essentially preventing the negotiation process resulting in fallback
to the use of cleartext. There have already been documented cases of
service providers preventing STARTTLS to avoid session encryption
negotiation on some sessions. Doing so allows them to inject a super
cookie that enables advertisers to track users; these actions are
also considered an attack. These serve as examples of undesirable
behavior that could be prevented through upfront discussions in
protocol work for operators and protocol designers to understand the
implications of such actions. In other cases, some service providers
and enterprises have relied on middleboxes having access to cleartext
for load-balancing, monitoring for attack traffic, meeting regulatory
requirements, or other purposes. The implications for enterprises
that own the data on their networks or that have explicit agreements
that permit the monitoring of user traffic are very different from
those for service providers who may be accessing content in a way
that violates privacy considerations. Additionally, service provider
equipment is designed for accessing only the headers exposed for the
data-link, network, and transport layers. Delving deeper into
packets is possible, but there is typically a high degree of accuracy
from the header information and packet sizes when limited to header
information from these three layers. Service providers also have the
option of adding routing overlay protocols to traffic. These
middlebox implementations, performing functions either considered
legitimate by the IETF or not, have been impacted by increases in
encrypted traffic. Only methods keeping with the goal of balancing
network management and pervasive monitoring mitigation as discussed
in [RFC7258] should be considered in work toward a solution resulting
from this document.
It is well known that national surveillance programs monitor traffic
for criminal activities [JNSLP] [RFC2804] [RFC7258]. Governments
vary on their balance between monitoring versus the protection of
user privacy, data, and assets. Those that favor unencrypted access
to data ignore the real need to protect users' identities, financial
transactions, and intellectual property (which require security and
encryption to prevent crime). A clear understanding of technology,
encryption, and monitoring goals will aid in the development of
solutions as work continues towards finding an appropriate balance
that allows for management while protecting user privacy with strong
encryption solutions.
2. Network Service Provider Monitoring Practices
Service providers, for this definition, include the backbone ISPs as
well as those providing infrastructure at scale for core Internet use
(hosted infrastructure and services such as email).
Network service providers use various techniques to operate, manage,
and secure their networks. The following subsections detail the
purpose of several techniques as well as which protocol fields are
used to accomplish each task. In response to increased encryption of
these fields, some network service providers may be tempted to
undertake undesirable security practices in order to gain access to
the fields in unencrypted data flows. To avoid this situation, new
methods could be developed to accomplish the same goals without
service providers having the ability to see session data.
2.1. Passive Monitoring
2.1.1. Traffic Surveys
Internet traffic surveys are useful in many pursuits, such as input
for studies of the Center for Applied Internet Data Analysis (CAIDA)
[CAIDA], network planning, and optimization. Tracking the trends in
Internet traffic growth, from earlier peer-to-peer communication to
the extensive adoption of unicast video streaming applications, has
relied on a view of traffic composition with a particular level of
assumed accuracy, based on access to cleartext by those conducting
the surveys.
Passive monitoring makes inferences about observed traffic using the
maximal information available and is subject to inaccuracies stemming
from incomplete sampling (of packets in a stream) or loss due to
monitoring-system overload. When encryption conceals more layers in
each packet, reliance on pattern inferences and other heuristics
grows and accuracy suffers. For example, the traffic patterns
between server and browser are dependent on browser supplier and
version, even when the sessions use the same server application
(e.g., web email access). It remains to be seen whether more complex
inferences can be mastered to produce the same monitoring accuracy.
2.1.2. Troubleshooting
Network operators use protocol-dissecting analyzers when responding
to customer problems, to identify the presence of attack traffic, and
to identify root causes of the problem such as misconfiguration. In
limited cases, packet captures may also be used when a customer
approves of access to their packets or provides packet captures close
to the endpoint. The protocol dissection is generally limited to
supporting protocols (e.g., DNS and DHCP), network and transport
(e.g., IP and TCP), and some higher-layer protocols (e.g., RTP and
the RTP Control Protocol (RTCP)). Troubleshooting will move closer
to the endpoint with increased encryption and adjustments in
practices to effectively troubleshoot using a 5-tuple may require
education. Packet-loss investigations, and those where access is
limited to a 2-tuple (IPsec tunnel mode), rely on network and
transport-layer headers taken at the endpoint. In this case,
captures on intermediate nodes are not reliable as there are far too
many cases of aggregate interfaces and alternate paths in service
provider networks.
Network operators are often the first ones called upon to investigate
application problems (e.g., "my HD video is choppy"), to first rule
out network and network services as a cause for the underlying issue.
When diagnosing a customer problem, the starting point may be a
particular application that isn't working. The ability to identify
the problem application's traffic is important, and packet capture
provided from the customer close to the edge may be used for this
purpose; IP address filtering is not useful for applications using
Content Delivery Networks (CDNs) or cloud providers. After
identifying the traffic, an operator may analyze the traffic
characteristics and routing of the traffic. This diagnostic step is
important to help determine the root cause before exploring if the
issue is directly with the application.
For example, by investigating packet loss (from TCP sequence and
acknowledgement numbers), Round-Trip Time (RTT) (from TCP timestamp
options or application-layer transactions, e.g., DNS or HTTP response
time), TCP receive-window size, packet corruption (from checksum
verification), inefficient fragmentation, or application-layer
problems, the operator can narrow the problem to a portion of the
network, server overload, client or server misconfiguration, etc.
Network operators may also be able to identify the presence of attack
traffic as not conforming to the application the user claims to be
using. In many instances, the exposed packet header is sufficient
for this type of troubleshooting.
One way of quickly excluding the network as the bottleneck during
troubleshooting is to check whether the speed is limited by the
endpoints. For example, the connection speed might instead be
limited by suboptimal TCP options, the sender's congestion window,
the sender temporarily running out of data to send, the sender
waiting for the receiver to send another request, or the receiver
closing the receive window. All this information can be derived from
the cleartext TCP header.
Packet captures and protocol-dissecting analyzers have been important
tools. Automated monitoring has also been used to proactively
identify poor network conditions, leading to maintenance and network
upgrades before user experience declines. For example, findings of
loss and jitter in Voice over IP (VoIP) traffic can be a predictor of
future customer dissatisfaction (supported by metadata from RTP/RTCP)
[RFC3550], or increases in DNS response time can generally make
interactive web browsing appear sluggish. But, to detect such
problems, the application or service stream must first be
distinguished from others.
When increased encryption is used, operators lose a source of data
that may be used to debug user issues. For example, IPsec obscures
TCP and RTP header information, while TLS and the Secure Real-time
Transport Protocol (SRTP) do not. Because of this, application-
server operators using increased encryption might be called upon more
frequently to assist with debugging and troubleshooting; thus, they
may want to consider what tools can be put in the hands of their
clients or network operators.
Further, the performance of some services can be more efficiently
managed and repaired when information on user transactions is
available to the service provider. It may be possible to continue
transaction-monitoring activities without cleartext access to the
application layers of interest; however, inaccuracy will increase and
efficiency of repair activities will decrease. For example, an
application-protocol error or failure would be opaque to network
troubleshooters when transport encryption is applied, making root
cause location more difficult and, therefore, increasing the time to
repair. Repair time directly reduces the availability of the
service, and most network operators have made availability a key
metric in their Service Level Agreements (SLAs) and/or subscription
rebates. Also, there may be more cases of user-communication
failures when the additional encryption processes are introduced
(e.g., key management at large scale), leading to more customer
service contacts and (at the same time) less information available to
network-operation repair teams.
In mobile networks, knowledge about TCP's stream transfer progress
(by observing ACKs, retransmissions, packet drops, and the Sector
Utilization Level, etc.) is further used to measure the performance
of network segments (sector, eNodeB (eNB), etc.). This information
is used as key performance indicators (KPIs) and for the estimation
of user/service key quality indicators at network edges for circuit
emulation (CEM) as well as input for mitigation methods. If the
makeup of active services per user and per sector are not visible to
a server that provides Internet Access Point Names (APNs), it cannot
perform mitigation functions based on network segment view.
It is important to note that the push for encryption by application
providers has been motivated by the application of the described
techniques. Although network operators have noted performance
improvements with network-based optimization or enhancement of user
traffic (otherwise, deployment would not have occurred), application
providers have likewise noted some degraded performance and/or user
experience, and such cases may result in additional operator
troubleshooting. Further, encrypted application streams might avoid
outdated optimization or enhancement techniques, where they exist.
A gap exists for vendors where built-in diagnostics and
serviceability are not adequate to provide detailed logging and
debugging capabilities that, when possible, could be accessed with
cleartext network parameters. In addition to traditional logging and
debugging methods, packet tracing and inspection along the service
path provides operators the visibility to continue to diagnose
problems reported both internally and by their customers. Logging of
service path upon exit for routing overlay protocols will assist with
policy management and troubleshooting capabilities for traffic flows
on encrypted networks. Protocol trace logging and protocol data unit
(PDU) logging should also be considered to improve visibility to
monitor and troubleshoot application-level traffic. Additional work
on this gap would assist network operators to better troubleshoot and
manage networks with increasing amounts of encrypted traffic.
2.1.3. Traffic-Analysis Fingerprinting
Fingerprinting is used in traffic analysis and monitoring to identify
traffic streams that match certain patterns. This technique can be
used with both cleartext and encrypted sessions. Some Distributed
Denial-of-Service (DDoS) prevention techniques at the network-
provider level rely on the ability to fingerprint traffic in order to
mitigate the effect of this type of attack. Thus, fingerprinting may
be an aspect of an attack or part of attack countermeasures.
A common, early trigger for DDoS mitigation includes observing
uncharacteristic traffic volumes or sources, congestion, or
degradation of a given network or service. One approach to mitigate
such an attack involves distinguishing attacker traffic from
legitimate user traffic. The ability to examine layers and payloads
above transport provides an increased range of filtering
opportunities at each layer in the clear. If fewer layers are in the
clear, this means that there are reduced filtering opportunities
available to mitigate attacks. However, fingerprinting is still
possible.
Passive monitoring of network traffic can lead to invasion of privacy
by external actors at the endpoints of the monitored traffic.
Encryption of traffic end to end is one method to obfuscate some of
the potentially identifying information. For example, browser
fingerprints are comprised of many characteristics, including User
Agents, HTTP Accept headers, browser plug-in details, screen size and
color details, system fonts, and time zones. A monitoring system
could easily identify a specific browser, and by correlating other
information, identify a specific user.
2.2. Traffic Optimization and Management
2.2.1. Load Balancers
A standalone load balancer is a function one can take off the shelf,
place in front of a pool of servers, and configure appropriately, and
it will balance the traffic load among servers in the pool. This is
a typical setup for load balancers. Standalone load balancers rely
on the plainly observable information in the packets they are
forwarding and industry-accepted standards in interpreting the
plainly observable information. Typically, this is a 5-tuple of the
connection. This type of configuration terminates TLS sessions at
the load balancer, making it the endpoint instead of the server.
Standalone load balancers are considered middleboxes, but they are an
integral part of server infrastructure that scales.
In contrast, an integrated load balancer is developed to be an
integral part of the service provided by the server pool behind that
load balancer. These load balancers can communicate state with their
pool of servers to better route flows to the appropriate servers.
They rely on non-standard, system-specific information and
operational knowledge shared between the load balancer and its
servers.
Both standalone and integrated load balancers can be deployed in
pools for redundancy and load sharing. For high availability, it is
important that when packets belonging to a flow start to arrive at a
different load balancer in the load-balancer pool, the packets
continue to be forwarded to the original server in the server pool.
The importance of this requirement increases as the chance of such a
load balancer change event increases.
Mobile operators deploy integrated load balancers to assist with
maintaining connection state as devices migrate. With the
proliferation of mobile connected devices, there is an acute need for
connection-oriented protocols that maintain connections after a
network migration by an endpoint. This connection persistence
provides an additional challenge for multihomed anycast-based
services typically employed by large content owners and CDNs. The
challenge is that a migration to a different network in the middle of
the connection greatly increases the chances of the packets routed to
a different anycast point of presence (POP) due to the new network's
different connectivity and Internet peering arrangements. The load
balancer in the new POP, potentially thousands of miles away, will
not have information about the new flow and would not be able to
route it back to the original POP.
To help with the endpoint network migration challenges, anycast
service operations are likely to employ integrated load balancers
that, in cooperation with their pool servers, are able to ensure that
client-to-server packets contain some additional identification in
plainly observable parts of the packets (in addition to the 5-tuple).
As noted in Section 2 of [RFC7258], careful consideration in protocol
design to mitigate pervasive monitoring is important, while ensuring
manageability of the network.
An area for further research includes end-to-end solutions that would
provide a simpler architecture and that may solve the issue with CDN
anycast. In this case, connections would be migrated to a CDN
unicast address.
Current protocols, such as TCP, allow the development of stateless
integrated load balancers by availing such load balancers of
additional plaintext information in client-to-server packets. In
case of TCP, such information can be encoded by having server-
generated sequence numbers (that are ACKed by the client), segment
values, lengths of the packet sent, etc. The use of some of these
mechanisms for load balancing negates some of the security
assumptions associated with those primitives (e.g., that an off-path
attacker guessing valid sequence numbers for a flow is hard).
Another possibility is a dedicated mechanism for storing load-
balancer state, such as QUIC's proposed connection ID to provide
visibility to the load balancer. An identifier could be used for
tracking purposes, but this may provide an option that is an
improvement from bolting it on to an unrelated transport signal.
This method allows for tight control by one of the endpoints and can
be rotated to avoid roving client linkability: in other words, being
a specific, separate signal, it can be governed in a way that is
finely targeted at that specific use case.
Some integrated load balancers have the ability to use additional
plainly observable information even for today's protocols that are
not network-migration tolerant. This additional information allows
for improved availability and scalability of the load-balancing
operation. For example, BGP reconvergence can cause a flow to switch
anycast POPs, even without a network change by any endpoint.
Additionally, a system that is able to encode the identity of the
pool server in plaintext information available in each incoming
packet is able to provide stateless load balancing. This ability
confers great reliability and scalability advantages, even if the
flow remains in a single POP, because the load-balancing system is
not required to keep state of each flow. Even more importantly,
there's no requirement to continuously synchronize such state among
the pool of load balancers. An integrated load balancer repurposing
limited existing bits in transport-flow state must maintain and
synchronize per-flow state occasionally: using the sequence number as
a cookie only works for so long given that there aren't that many
bits available to divide across a pool of machines.
Mobile operators apply 3GPP Self-Organizing Networks (SONs) for
intelligent workflows such as content-aware Mobility Load Balancing
(MLB). Where network load balancers have been configured to route
according to application-layer semantics, an encrypted payload is
effectively invisible. This has resulted in practices of
intercepting TLS in front of load balancers to regain that
visibility, but at a cost to security and privacy.
In future Network Function Virtualization (NFV) architectures, load-
balancing functions are likely to be more prevalent (deployed at
locations throughout operators' networks). NFV environments will
require some type of identifier (IPv6 flow identifiers, the proposed
QUIC connection ID, etc.) for managing traffic using encrypted
tunnels. The shift to increased encryption will have an impact on
visibility of flow information and will require adjustments to
perform similar load-balancing functions within an NFV.
2.2.2. Differential Treatment Based on Deep Packet Inspection (DPI)
Data transfer capacity resources in cellular radio networks tend to
be more constrained than in fixed networks. This is a result of
variance in radio signal strength as a user moves around a cell, the
rapid ingress and egress of connections as users hand off between
adjacent cells, and temporary congestion at a cell. Mobile networks
alleviate this by queuing traffic according to its required bandwidth
and acceptable latency: for example, a user is unlikely to notice a
20 ms delay when receiving a simple web page or email, or an instant
message response, but will very likely notice a rebuffering pause in
a video playback or a VoIP call de-jitter buffer. Ideally, the
scheduler manages the queue so that each user has an acceptable
experience as conditions vary, but inferences of the traffic type
have been used to make bearer assignments and set scheduler priority.
Deep Packet Inspection (DPI) allows identification of applications
based on payload signatures, in contrast to trusting well-known port
numbers. Application- and transport-layer encryption make the
traffic type estimation more complex and less accurate; therefore, it
may not be effectual to use this information as input for queue
management. With the use of WebSockets [RFC6455], for example, many
forms of communications (from isochronous/real-time to bulk/elastic
file transfer) will take place over HTTP port 80 or port 443, so only
the messages and higher-layer data will make application
differentiation possible. If the monitoring system sees only "HTTP
port 443", it cannot distinguish application streams that would
benefit from priority queuing from others that would not.
Mobile networks especially rely on content-/application-based
prioritization of Over-the-Top (OTT) services -- each application
type or service has different delay/loss/throughput expectations, and
each type of stream will be unknown to an edge device if encrypted.
This impedes dynamic QoS adaptation. An alternate way to achieve
encrypted application separation is possible when the User Equipment
(UE) requests a dedicated bearer for the specific application stream
(known by the UE), using a mechanism such as the one described in
Section 6.5 of 3GPP TS 24.301 [TS3GPP]. The UE's request includes
the Quality Class Indicator (QCI) appropriate for each application,
based on their different delay/loss/throughput expectations.
However, UE requests for dedicated bearers and QCI may not be
supported at the subscriber's service level, or in all mobile
networks.
These effects and potential alternative solutions have been discussed
at the accord BoF [ACCORD] at IETF 95.
This section does not consider traffic discrimination by service
providers related to Net Neutrality, where traffic may be favored
according to the service provider's preference as opposed to the
user's preference. These use cases are considered out of scope for
this document as controversial practices.
2.2.3. Network-Congestion Management
For 3GPP User Plane Congestion Management (UPCON) [UPCON], the
ability to understand content and manage networks during periods of
congestion is the focus. Mitigating techniques such as deferred
download, off-peak acceleration, and outbound roamers are a few
examples of the areas explored in the associated 3GPP documents. The
documents describe the issues, describe the data utilized in managing
congestion, and make policy recommendations.
2.2.4. Performance-Enhancing Proxies
Performance-enhancing TCP proxies may perform local retransmission at
the network edge; this also applies to mobile networks. In TCP,
duplicated ACKs are detected and potentially concealed when the proxy
retransmits a segment that was lost on the mobile link without
involvement of the far end (see Section 2.1.1 of [RFC3135] and
Section 3.5 of [MIDDLEBOXES]).
Operators report that this optimization at network edges improves
real-time transmission over long-delay Internet paths or networks
with large capacity variation (such as mobile/cellular networks).
However, such optimizations can also cause problems with performance,
for example, if the characteristics of some packet streams begin to
vary significantly from those considered in the proxy design.
In general, some operators have stated that performance-enhancing
proxies have a lower RTT to the client; therefore, they determine the
responsiveness of flow control. A lower RTT makes the flow-control
loop more responsive to changes in the mobile-network conditions and
enables faster adaptation in a delay- and capacity-varying network
due to user mobility.
Further, some use service-provider-operated proxies to reduce the
control delay between the sender and a receiver on a mobile network
where resources are limited. The RTT determines how quickly a user's
attempt to cancel a video is recognized and, therefore, how quickly
the traffic is stopped, thus keeping unwanted video packets from
entering the radio-scheduler queue. If impacted by encryption,
performance-enhancing proxies could make use of routing overlay
protocols to accomplish the same task, but this results in additional
overhead.
An application-type-aware network edge (middlebox) can further
control pacing, limit simultaneous HD videos, or prioritize active
videos against new videos, etc. Services at this more granular level
are limited with the use of encryption.
Performance-enhancing proxies are primarily used on long-delay links
(satellite) with access to the TCP header to provide an early ACK and
make the long-delay link of the path seem shorter. With some
specific forms of flow control, TCP can be more efficient than
alternatives such as proxies. The editors cannot cite research on
this point specific to the performance-enhancing proxies described,
but they agree this area could be explored to determine if flow-
control modifications could preserve the end-to-end performance on
long-delay path sessions where the TCP header is exposed.
2.2.5. Caching and Content Replication near the Network Edge
The features and efficiency of some Internet services can be
augmented through analysis of user flows and the applications they
provide. For example, network caching of popular content at a
location close to the requesting user can improve delivery efficiency
(both in terms of lower request response times and reduced use of
links on the international Internet when content is remotely
located), and service providers through an authorized agreement
acting on their behalf use DPI in combination with content-
distribution networks to determine if they can intervene effectively.
Encryption of packet contents at a given protocol layer usually makes
DPI processing of that layer and higher layers impossible. That
being said, it should be noted that some content providers prevent
caching to control content delivery through the use of encrypted
end-to-end sessions. CDNs vary in their deployment options of end-
to-end encryption. The business risk of losing control of content is
a motivation outside of privacy and pervasive monitoring that is
driving end-to-end encryption for these content providers.
It should be noted that caching was first supported in [RFC1945] and
continued in the recent update of "Hypertext Transfer Protocol
(HTTP/1.1): Caching" [RFC7234]. Some operators also operate
transparent caches that neither the user nor the origin opt-in. The
use of these caches is controversial within the IETF and is generally
precluded by the use of HTTPS.
Content replication in caches (for example, live video and content
protected by Digital Rights Management (DRM)) is used to most
efficiently utilize the available limited bandwidth and thereby
maximize the user's Quality of Experience (QoE). Especially in
mobile networks, duplicating every stream through the transit network
increases backhaul cost for live TV. 3GPP Enhanced Multimedia
Broadcast/Multicast Services (eMBMS) utilize trusted edge proxies to
facilitate delivering the same stream to different users, using
either unicast or multicast depending on channel conditions to the
user. There are ongoing efforts to support multicast inside carrier
networks while preserving end-to-end security: Automatic Multicast
Tunneling (AMT), for instance, allows CDNs to deliver a single
(potentially encrypted) copy of a live stream to a carrier network
over the public Internet and for the carrier to then distribute that
live stream as efficiently as possible within its own network using
multicast.
Alternate approaches are in the early phase of being explored to
allow caching of encrypted content. These solutions require
cooperation from content owners and fall outside the scope of what is
covered in this document. Content delegation allows for replication
with possible benefits, but any form of delegation has the potential
to affect the expectation of client-server confidentiality.
2.2.6. Content Compression
In addition to caching, various applications exist to provide data
compression in order to conserve the life of the user's mobile data
plan or make delivery over the mobile link more efficient. The
compression proxy access can be built into a specific user-level
application, such as a browser, or it can be available to all
applications using a system-level application. The primary method is
for the mobile application to connect to a centralized server as a
transparent proxy (user does not opt-in), with the data channel
between the client application and the server using compression to
minimize bandwidth utilization. The effectiveness of such systems
depends on the server having access to unencrypted data flows.
Aggregated data stream content compression that spans objects and
data sources that can be treated as part of a unified compression
scheme (e.g., through the use of a shared segment store) is often
effective at providing data offload when there is a network element
close to the receiver that has access to see all the content.
2.2.7. Service Function Chaining
Service Function Chaining (SFC) is defined in RFC 7665 [RFC7665] and
RFC 8300 [RFC8300]. As discussed in RFC 7498 [RFC7498], common SFC
deployments may use classifiers to direct traffic into VLANs instead
of using a Network Service Header (NSH), as defined in RFC 8300
[RFC8300]. As described in RFC 7665 [RFC7665], the ordered steering
of traffic to support specific optimizations depends upon the ability
of a classifier to determine the microflows. RFC 2474 [RFC2474]
defines the following:
Microflow: a single instance of an application-to-application flow
of packets which is identified by source address, destination
address, protocol id, and source port, destination port (where
applicable).
SFC currently depends upon a classifier to at least identify the
microflow. As the classifier's visibility is reduced from a 5-tuple
to a 2-tuple, or if information above the transport layer becomes
inaccessible, then the SFC classifier is not able to perform its job,
and the service functions of the path may be adversely affected.
There are also mechanisms provided to protect security and privacy.
In the SFC case, the layer below a network service header can be
protected with session encryption. A goal is protecting end-user
data, while retaining the intended functions of RFC 7665 [RFC7665] at
the same time.
2.3. Content Filtering, Network Access, and Accounting
Mobile networks and many ISPs operate under the regulations of their
licensing government authority. These regulations include Lawful
Intercept, adherence to Codes of Practice on content filtering, and
application of court order filters. Such regulations assume network
access to provide content filtering and accounting, as discussed
below. As previously stated, the intent of this document is to
document existing practices; the development of IETF protocols
follows the guiding principles of [RFC1984] and [RFC2804] and
explicitly does not support tools and methods that could be used for
wiretapping and censorship.
2.3.1. Content Filtering
There are numerous reasons why service providers might block content:
to comply with requests from law enforcement or regulatory
authorities, to effectuate parental controls, to enforce content-
based billing, or for other reasons, possibly considered
inappropriate by some. See RFC 7754 [RFC7754] for a survey of
Internet filtering techniques and motivations and the IAB consensus
on those mechanisms. This section is intended to document a
selection of current content-blocking practices by operators and the
effects of encryption on those practices. Content blocking may also
happen at endpoints or at the edge of enterprise networks, but those
scenarios are not addressed in this section.
In a mobile network, content filtering usually occurs in the core
network. With other networks, content filtering could occur in the
core network or at the edge. A proxy is installed that analyzes the
transport metadata of the content users are viewing and filters
content based on either a blacklist of sites or the user's predefined
profile (e.g., for age-sensitive content). Although filtering can be
done by many methods, one commonly used method involves a trigger
based on the proxy identifying a DNS lookup of a host name in a URL
that appears on a blacklist being used by the operator. The
subsequent requests to that domain will be rerouted to a proxy that
checks whether the full URL matches a blocked URL on the list, and it
will return a 404 if a match is found. All other requests should
complete. This technique does not work in situations where DNS
traffic is encrypted (e.g., by employing [RFC7858]). This method is
also used by other types of network providers enabling traffic
inspection, but not modification.
Content filtering via a proxy can also utilize an intercepting
certificate where the client's session is terminated at the proxy
enabling for cleartext inspection of the traffic. A new session is
created from the intercepting device to the client's destination;
this is an opt-in strategy for the client, where the endpoint is
configured to trust the intercepting certificate. Changes to TLS 1.3
do not impact this more invasive method of interception, which has
the potential to expose every HTTPS session to an active man in the
middle (MITM).
Another form of content filtering is called parental control, where
some users are deliberately denied access to age-sensitive content as
a feature to the service subscriber. Some sites involve a mixture of
universal and age-sensitive content and filtering software. In these
cases, more-granular (application-layer) metadata may be used to
analyze and block traffic. Methods that accessed cleartext
application-layer metadata no longer work when sessions are
encrypted. This type of granular filtering could occur at the
endpoint or as a proxy service. However, the lack of ability to
efficiently manage endpoints as a service reduces network service
providers' ability to offer parental control.
2.3.2. Network Access and Data Usage
Approved access to a network is a prerequisite to requests for
Internet traffic.
However, there are cases (beyond parental control) when a network
service provider currently redirects customer requests for content
(affecting content accessibility):
1. The network service provider is performing the accounting and
billing for the content provider, and the customer has not (yet)
purchased the requested content.
2. Further content may not be allowed as the customer has reached
their usage limit and needs to purchase additional data service,
which is the usual billing approach in mobile networks.
Currently, some network service providers redirect the customer using
HTTP redirect to a captive portal page that explains to those
customers the reason for the blockage and the steps to proceed.
[RFC6108] describes one viable web notification system. When the
HTTP headers and content are encrypted, this appropriately prevents
mobile carriers from intercepting the traffic and performing an HTTP
redirect. As a result, some mobile carriers block customer's
encrypted requests, which impacts customer experience because the
blocking reason must be conveyed by some other means. The customer
may need to call customer care to find out the reason and/or resolve
the issue, possibly extending the time needed to restore their
network access. While there are well-deployed alternate SMS-based
solutions that do not involve out-of-specification protocol
interception, this is still an unsolved problem for non-SMS users.
Further, when the requested service is about to consume the remainder
of the user's plan limits, the transmission could be terminated and
advance notifications may be sent to the user by their service
provider to warn the user ahead of the exhausted plan. If web
content is encrypted, the network provider cannot know the data
transfer size at request time. Lacking this visibility of the
application type and content size, the network would continue the
transmission and stop the transfer when the limit was reached. A
partial transfer may not be usable by the client wasting both network
and user resources, possibly leading to customer complaints. The
content provider does not know a user's service plans or current
usage and cannot warn the user of plan exhaustion.
In addition, some mobile network operators sell tariffs that allow
free-data access to certain sites, known as 'zero rating'. A session
to visit such a site incurs no additional cost or data usage to the
user. For some implementations, zero rating is impacted if
encryption hides the details of the content domain from the network.
2.3.3. Application Layer Gateways (ALGs)
Application Layer Gateways (ALGs) assist applications to set
connectivity across Network Address Translators (NATs), firewalls,
and/or load balancers for specific applications running across mobile
networks. Section 2.9 of [RFC2663] describes the role of ALGs and
their interaction with NAT and/or application payloads. ALGs are
deployed with an aim to improve connectivity. However, it is an IETF
best common practice recommendation that ALGs for UDP-based protocols
be turned off [RFC4787].
One example of an ALG in current use is aimed at video applications
that use the Real-Time Streaming Protocol (RTSP) [RFC7826] primary
stream as a means to identify related RTP/RTCP [RFC3550] flows at
setup. The ALG in this case relies on the 5-tuple flow information
derived from RTSP to provision NAT or other middleboxes and provide
connectivity. Implementations vary, and two examples follow:
1. Parse the content of the RTSP stream and identify the 5-tuple of
the supporting streams as they are being negotiated.
2. Intercept and modify the 5-tuple information of the supporting
media streams as they are being negotiated on the RTSP stream,
which is more intrusive to the media streams.
When RTSP-stream content is encrypted, the 5-tuple information within
the payload is not visible to these ALG implementations; therefore,
they cannot provision their associated middleboxes with that
information.
The deployment of IPv6 may well reduce the need for NAT and the
corresponding requirement for ALGs.
2.3.4. HTTP Header Insertion
Some mobile carriers use HTTP header insertion (see Section 3.2.1 of
[RFC7230]) to provide information about their customers to third
parties or to their own internal systems [Enrich]. Third parties use
the inserted information for analytics, customization, advertising,
cross-site tracking of users, customer billing, or selectively
allowing or blocking content. HTTP header insertion is also used to
pass information internally between a mobile service provider's
sub-systems, thus keeping the internal systems loosely coupled. When
HTTP connections are encrypted to protect user privacy, mobile
network service providers cannot insert headers to accomplish the,
sometimes considered controversial, functions above.
Guidance from the Internet Architecture Board has been provided in
"Design Considerations for Metadata Insertion" [RFC8165]. The
guidance asserts that designs that share metadata only by explicit
actions at the host are preferable to designs in which middleboxes
insert metadata. Alternate notification methods that follow this and
other guidance would be helpful to mobile carriers.
3. Encryption in Hosting and Application SP Environments
Hosted environments have had varied requirements in the past for
encryption, with many businesses choosing to use these services
primarily for data and applications that are not business or privacy
sensitive. A shift prior to the revelations on surveillance/passive
monitoring began where businesses were asking for hosted environments
to provide higher levels of security so that additional applications
and service could be hosted externally. Businesses understanding the
threats of monitoring in hosted environments increased that pressure
to provide more secure access and session encryption to protect the
management of hosted environments as well as the data and
applications.
3.1. Management-Access Security
Hosted environments may have multiple levels of management access,
where some may be strictly for the Hosting service provider
(infrastructure that may be shared among customers), and some may be
accessed by a specific customer for application management. In some
cases, there are multiple levels of hosting service providers,
further complicating the security of management infrastructure and
the associated requirements.
Hosting service provider management access is typically segregated
from other traffic with a control channel and may or may not be
encrypted depending upon the isolation characteristics of the
management session. Customer access may be through a dedicated
connection, but discussion for that connection method is out of scope
for this document.
In overlay networks (e.g., Virtual eXtensible Local Area Network
(VXLAN), Geneve, etc.) that are used to provide hosted services,
management access for a customer to support application management
may depend upon the security mechanisms available as part of that
overlay network. While overlay-network data encapsulations may be
used to indicate the desired isolation, this is not sufficient to
prevent deliberate attacks that are aware of the use of the overlay
network. [GENEVE-REQS] describes requirements to handle attacks. It
is possible to use an overlay header in combination with IPsec or
other encrypted traffic sessions, but this adds the requirement for
authentication infrastructure and may reduce packet transfer
performance. The use of an overlay header may also be deployed as a
mechanism to manage encrypted traffic streams on the network-by-
network service providers. Additional extension mechanisms to
provide integrity and/or privacy protections are being investigated
for overlay encapsulations. Section 7 of [RFC7348] describes some of
the security issues possible when deploying VXLAN on Layer 2
networks. Rogue endpoints can join the multicast groups that carry
broadcast traffic, for example.
3.1.1. Monitoring Customer Access
Hosted applications that allow some level of customer-management
access may also require monitoring by the hosting service provider.
Monitoring could include access-control restrictions such as
authentication, authorization, and accounting for filtering and
firewall rules to ensure they are continuously met. Customer access
may occur on multiple levels, including user-level and administrative
access. The hosting service provider may need to monitor access
through either session monitoring or log evaluation to ensure
security SLAs for access management are met. The use of session
encryption to access hosted environments limits access restrictions
to the metadata described below. Monitoring and filtering may occur
at a:
2-tuple: IP level with source and destination IP addresses alone, or
5-tuple: IP and protocol level with a source IP address, destination
IP address, protocol number, source port number, and destination
port number.
Session encryption at the application level, for example, TLS,
currently allows access to the 5-tuple. IP-level encryption, such as
IPsec in tunnel mode, prevents access to the original 5-tuple and may
limit the ability to restrict traffic via filtering techniques. This
shift may not impact all hosting service provider solutions as
alternate controls may be used to authenticate sessions, or access
may require that clients access such services by first connecting to
the organization before accessing the hosted application. Shifts in
access may be required to maintain equivalent access-control
management. Logs may also be used for monitoring that access-control
restrictions are met, but would be limited to the data that could be
observed due to encryption at the point of log generation. Log
analysis is out of scope for this document.
3.1.2. SP Content Monitoring of Applications
The following observations apply to any IT organization that is
responsible for delivering services, whether to third parties, for
example, as a web-based service, or to internal customers in an
enterprise, e.g., a data-processing system that forms a part of the
enterprise's business.
Organizations responsible for the operation of a data center have
many processes that access the contents of IP packets (passive
methods of measurement, as defined in [RFC7799]). These processes
are typically for service assurance or security purposes as part of
their data-center operations.
Examples include:
- Network-Performance Monitoring / Application-Performance
Monitoring
- Intrusion defense/prevention systems
- Malware detection
- Fraud monitoring
- Application DDOS protection
- Cyber-attack investigation
- Proof of regulatory compliance
- Data leakage prevention
Many application service providers simply terminate sessions to/from
the Internet at the edge of the data center in the form of SSL/TLS
offload in the load balancer. Not only does this reduce the load on
application servers, it simplifies the processes to enable monitoring
of the session content.
However, in some situations, encryption deeper in the data center may
be necessary to protect personal information or in order to meet
industry regulations, e.g., those set out by the Payment Card
Industry (PCI). In such situations, various methods have been used
to allow service assurance and security processes to access
unencrypted data. These include SSL/TLS decryption in dedicated
units, which then forward packets to SP-controlled tools, or real-
time or post-capture decryption in the tools themselves. A number of
these tools provide passive decryption by providing the monitoring
device with the server's private key. The move to increased use of
the forward-secret key exchange mechanism impacts the use of these
techniques.
Operators of data centers may also maintain packet recordings in
order to be able to investigate attacks, breaches of internal
processes, etc. In some industries, organizations may be legally
required to maintain such information for compliance purposes.
Investigations of this nature have used access to the unencrypted
contents of the packet. Alternate methods to investigate attacks or
breaches of process will rely on endpoint information, such as logs.
As previously noted, logs often lack complete information, and this
is seen as a concern resulting in some relying on session access for
additional information.
Application service providers may offer content-level monitoring
options to detect intellectual property leakage or other attacks. In
service provider environments where Data Loss Prevention (DLP) has
been implemented on the basis of the service provider having
cleartext access to session streams, the use of encrypted streams
prevents these implementations from conducting content searches for
the keywords or phrases configured in the DLP system. DLP is often
used to prevent the leakage of Personally Identifiable Information
(PII) as well as financial account information, Personal Health
Information (PHI), and PCI. If session encryption is terminated at a
gateway prior to accessing these services, DLP on session data can
still be performed. The decision of where to terminate encryption to
hosted environments will be a risk decision made between the
application service provider and customer organization according to
their priorities. DLP can be performed at the server for the hosted
application and on an end user's system in an organization as
alternate or additional monitoring points of content; however, this
is not frequently done in a service provider environment.
Application service providers, by their very nature, control the
application endpoint. As such, much of the information gleaned from
sessions is still available on that endpoint. However, when a gap
exists in the application's logging and debugging capabilities, it
has led the application service provider to access data in transport
for monitoring and debugging.
3.2. Hosted Applications
Organizations are increasingly using hosted applications rather than
in-house solutions that require maintenance of equipment and
software. Examples include Enterprise Resource Planning (ERP)
solutions, payroll service, time and attendance, travel and expense
reporting, among others. Organizations may require some level of
management access to these hosted applications and will typically
require session encryption or a dedicated channel for this activity.
In other cases, hosted applications may be fully managed by a hosting
service provider with SLA expectations for availability and
performance as well as for security functions including malware
detection. Due to the sensitive nature of these hosted environments,
the use of encryption is already prevalent. Any impact may be
similar to an enterprise with tools being used inside of the hosted
environment to monitor traffic. Additional concerns were not
reported in the call for contributions.
3.2.1. Monitoring Managed Applications
Performance, availability, and other aspects of an SLA are often
collected through passive monitoring. For example:
o Availability: ability to establish connections with hosts to
access applications and to discern the difference between network-
or host-related causes of unavailability.
o Performance: ability to complete transactions within a target
response time and to discern the difference between network- or
host-related causes of excess response time.
Here, as with all passive monitoring, the accuracy of inferences is
dependent on the cleartext information available, and encryption
would tend to reduce the information and, therefore, the accuracy of
each inference. Passive measurement of some metrics will be
impossible with encryption that prevents inferring-packet
correspondence across multiple observation points, such as for
packet-loss metrics.
Application logging currently lacks detail sufficient to make
accurate inferences in an environment with increased encryption, and
so this constitutes a gap for passive performance monitoring (which
could be closed if log details are enhanced in the future).
3.2.2. Mail Service Providers
Mail (application) service providers vary in what services they
offer. Options may include a fully hosted solution where mail is
stored external to an organization's environment on mail service
provider equipment or the service offering may be limited to monitor
incoming mail to remove spam (Section 5.1), phishing attacks
(Section 5.3), and malware (Section 5.6) before mail is directed to
the organization's equipment. In both of these cases, content of the
messages and headers is monitored to detect and remove messages that
are undesirable or that may be considered an attack.
STARTTLS should have zero effect on anti-spam efforts for SMTP
traffic. Anti-spam services could easily be performed on an SMTP
gateway, eliminating the need for TLS decryption services. The
impact to anti-spam service providers should be limited to a change
in tools, where middleboxes were deployed to perform these functions.
Many efforts are emerging to improve user-to-user encryption,
including promotion of PGP and newer efforts such as Dark Mail
[DarkMail]. Of course, content-based spam filtering will not be
possible on encrypted content.
3.3. Data Storage
Numerous service offerings exist that provide hosted storage
solutions. This section describes the various offerings and details
the monitoring for each type of service and how encryption may impact
the operational and security monitoring performed.
Trends in data storage encryption for hosted environments include a
range of options. The following list is intentionally high-level to
describe the types of encryption used in coordination with data
storage that may be hosted remotely, meaning the storage is
physically located in an external data center requiring transport
over the Internet. Options for monitoring will vary with each
encryption approach described below. In most cases, solutions have
been identified to provide encryption while ensuring management
capabilities were maintained through logging or other means.
3.3.1. Object-Level Encryption
For higher security and/or privacy of data and applications, options
that provide end-to-end encryption of the data from the user's
desktop or server to the storage platform may be preferred. This
description includes any solution that encrypts data at the object
level, not the transport level. Encryption of data may be performed
with libraries on the system or at the application level, which
includes file-encryption services via a file manager. Object-level
encryption is useful when data storage is hosted or scenarios when
the storage location is determined based on capacity or based on a
set of parameters to automate decisions. This could mean that large
datasets accessed infrequently could be sent to an off-site storage
platform at an external hosting service, data accessed frequently may
be stored locally, or the decision of where to store datasets could
be based on the transaction type. Object-level encryption is grouped
separately for the purpose of this document since data may be stored
in multiple locations including off-site remote storage platforms.
If session encryption is also used, the protocol is likely to be TLS.
Impacts to monitoring may include access to content inspection for
data-leakage prevention and similar technologies, depending on their
placement in the network.
3.3.1.1. Monitoring for Hosted Storage
Monitoring of hosted storage solutions that use host-level (object)
encryption is described in this subsection. Host-level encryption
can be employed for backup services and occasionally for external
storage services (operated by a third party) when internal storage
limits are exceeded.
Monitoring of data flows to hosted storage solutions is performed for
security and operational purposes. The security monitoring may be to
detect anomalies in the data flows that could include changes to
destination, the amount of data transferred, or alterations in the
size and frequency of flows. Operational considerations include
capacity and availability monitoring.
3.3.2. Disk Encryption, Data at Rest (DAR)
There are multiple ways to achieve full disk encryption for stored
data. Encryption may be performed on data to be stored while in
transit close to the storage media with solutions like Controller
Based Encryption (CBE) or in the drive system with Self-Encrypting
Drives (SEDs). Session encryption is typically coupled with
encryption of these data at rest (DAR) solutions to also protect data
in transit. Transport encryption is likely via TLS.
3.3.2.1. Monitoring Session Flows for DAR Solutions
Monitoring for transport of data-to-storage platforms, where object-
level encryption is performed close to or on the storage platform, is
similar to that described in Section 3.3.1.1. The primary difference
for these solutions is the possible exposure of sensitive
information, which could include privacy-related data, financial
information, or intellectual property if session encryption via TLS
is not deployed. Session encryption is typically used with these
solutions, but that decision would be based on a risk assessment.
There are use cases where DAR or disk-level encryption is required.
Examples include preventing exposure of data if physical disks are
stolen or lost. In the case where TLS is in use, monitoring and the
exposure of data is limited to a 5-tuple.
3.3.3. Cross-Data-Center Replication Services
Storage services also include data replication, which may occur
between data centers and may leverage Internet connections to tunnel
traffic. The traffic may use an Internet Small Computer System
Interface (iSCSI) [RFC7143] or Fibre Channel over TCP/IP (FCIP)
[RFC7146] encapsulated in IPsec. Either transport or tunnel mode may
be used for IPsec depending upon the termination points of the IPsec
session, if it is from the storage platform itself or from a gateway
device at the edge of the data center, respectively.
3.3.3.1. Monitoring IPsec for Data Replication Services
The monitoring of data flows between data centers (for data
replication) may be performed for security and operational purposes
and would typically concentrate more on operational aspects since
these flows are essentially virtual private networks (VPNs) between
data centers. Operational considerations include capacity and
availability monitoring. The security monitoring may be to detect
anomalies in the data flows, similar to what was described in
Section 3.3.1.1. If IPsec tunnel mode is in use, monitoring is
limited to a 2-tuple; with transport mode, it's limited to a 5-tuple.
4. Encryption for Enterprises
Encryption of network traffic within the private enterprise is a
growing trend, particularly in industries with audit and regulatory
requirements. Some enterprise-internal networks are almost
completely TLS and/or IPsec encrypted.
For each type of monitoring, different techniques and access to parts
of the data stream are part of current practice. As we transition to
an increased use of encryption, alternate methods of monitoring for
operational purposes may be necessary to reduce the practice of
breaking encryption (other policies may apply in some enterprise
settings).
4.1. Monitoring Practices of the Enterprise
Large corporate enterprises are the owners of the platforms, data,
and network infrastructure that provide critical business services to
their user communities. As such, these enterprises are responsible
for all aspects of the performance, availability, security, and
quality of experience for all user sessions. In many such
enterprises, users are required to consent to the enterprise
monitoring all their activities as a condition of employment.
Subsections of Section 4 discuss techniques that access data beyond
the data-link, network, and transport-level headers typically used in
service provider networks since the corporate enterprise owns the
data. These responsibilities break down into three basic areas:
1. Security Monitoring and Control
2. Application-Performance Monitoring and Reporting
3. Network Diagnostics and Troubleshooting
In each of the above areas, technical support teams utilize
collection, monitoring, and diagnostic systems. Some organizations
currently use attack methods such as replicated TLS server RSA
private keys to decrypt passively monitored copies of encrypted TLS
packet streams.
For an enterprise to avoid costly application down time and deliver
expected levels of performance, protection, and availability, some
forms of traffic analysis, sometimes including examination of packet
payloads, are currently used.
4.1.1. Security Monitoring in the Enterprise
Enterprise users are subject to the policies of their organization
and the jurisdictions in which the enterprise operates. As such,
proxies may be in use to:
1. intercept outbound session traffic to monitor for intellectual
property leakage (by users, malware, and trojans),
2. detect viruses/malware entering the network via email or web
traffic,
3. detect malware/trojans in action, possibly connecting to remote
hosts,
4. detect attacks (cross-site scripting and other common web-related
attacks),
5. track misuse and abuse by employees,
6. restrict the types of protocols permitted to/from the entire
corporate environment, and
7. detect and defend against Internet DDoS attacks, including both
volumetric and Layer 7 attacks.
A significant portion of malware hides its activity within TLS or
other encryption protocols. This includes lateral movement, Command
and Control (C&C), and Data Exfiltration.
The impact to a fully encrypted internal network would include cost
and possible loss of detection capabilities associated with the
transformation of the network architecture and tools for monitoring.
The capabilities of detection through traffic fingerprinting,
logging, host-level transaction monitoring, and flow analysis would
vary depending on access to a 2-tuple or 5-tuple in the network as
well.
Security monitoring in the enterprise may also be performed at the
endpoint with numerous current solutions that mitigate the same
problems as some of the above-mentioned solutions. Since the
software agents operate on the device, they are able to monitor
traffic before it is encrypted, monitor for behavior changes and lock
down devices to use only the expected set of applications. Session
encryption does not affect these solutions. Some might argue that
scaling is an issue in the enterprise, but some large enterprises
have used these tools effectively.
Use of bring-your-own-device (BYOD) policies within organizations may
limit the scope of monitoring permitted with these alternate
solutions. Network endpoint assessment (NEA) or the use of virtual
hosts could help to bridge the monitoring gap.
4.1.2. Monitoring Application Performance in the Enterprise
There are two main goals of monitoring:
1. Assess traffic volume on a per-application basis for billing,
capacity planning, optimization of geographical location for
servers or proxies, and other goals.
2. Assess performance in terms of application response time and
user-perceived response time.
Network-based application-performance monitoring tracks application
response time by user and by URL, which is the information that the
application owners and the lines of business request. CDNs add
complexity in determining the ultimate endpoint destination. By
their very nature, such information is obscured by CDNs and encrypted
protocols, adding a new challenge for troubleshooting network and
application problems. URL identification allows the application
support team to do granular, code-level troubleshooting at multiple
tiers of an application.
New methodologies to monitor user-perceived response time and to
separate network from server time are evolving. For example, the
IPv6 Destination Option Header (DOH) implementation of Performance
and Diagnostic Metrics (PDM) [RFC8250] will provide this. Using PDM
with IPsec Encapsulating Security Payload (ESP) Transport Mode
requires placement of the PDM DOH within the ESP-encrypted payload to
avoid leaking timing and sequence number information that could be
useful to an attacker. Use of PDM DOH also may introduce some
security weaknesses, including a timing attack, as described in
Section 4 of [RFC8250]. For these and other reasons, [RFC8250]
requires that the PDM DOH option be explicitly turned on by
administrative action in each host where this measurement feature
will be used.
4.1.3. Diagnostics and Troubleshooting for Enterprise Networks
One primary key to network troubleshooting is the ability to follow a
transaction through the various tiers of an application in order to
isolate the fault domain. A variety of factors relating to the
structure of the modern data center and multi-tiered application have
made it difficult to follow a transaction in network traces without
the ability to examine some of the packet payload. Alternate
methods, such as log analysis, need improvement to fill this gap.
4.1.3.1. Address Sharing (NAT)
CDNs, NATs, and Network Address and Port Translators (NAPTs) obscure
the ultimate endpoint designation (see [RFC6269] for types of address
sharing and a list of issues). Troubleshooting a problem for a
specific end user requires finding information such as the IP address
and other identifying information so that their problem can be
resolved in a timely manner.
NAT is also frequently used by lower layers of the data-center
infrastructure. Firewalls, load balancers, web servers, app servers,
and middleware servers all regularly NAT the source IP of packets.
Combine this with the fact that users are often allocated randomly by
load balancers to all these devices, and the network troubleshooter
is often left with very few options in today's environment due to
poor logging implementations in applications. As such, network
troubleshooting is used to trace packets at a particular layer,
decrypt them, and look at the payload to find a user session.
This kind of bulk packet capture and bulk decryption is frequently
used when troubleshooting a large and complex application. Endpoints
typically don't have the capacity to handle this level of network
packet capture, so out-of-band networks of robust packet brokers and
network sniffers that use techniques such as copies of TLS RSA
private keys accomplish this task today.
4.1.3.2. TCP Pipelining / Session Multiplexing
TCP pipelining / session multiplexing used mainly by middleboxes
today allows for multiple end-user sessions to share the same TCP
connection. This raises several points of interest with an increased
use of encryption. TCP session multiplexing should still be possible
when TLS or TCPcrypt is in use since the TCP header information is
exposed, leaving the 5-tuple accessible. The use of TCP session
multiplexing of an IP-layer encryption, e.g., IPsec, that only
exposes a 2-tuple would not be possible. Troubleshooting
capabilities with encrypted sessions from the middlebox may limit
troubleshooting to the use of logs from the endpoints performing the
TCP multiplexing or from the middleboxes prior to any additional
encryption that may be added to tunnel the TCP multiplexed traffic.
Increased use of HTTP/2 will likely further increase the prevalence
of session multiplexing, both on the Internet and in the private data
center. HTTP pipelining requires both the client and server to
participate; visibility of packets once encrypted will hide the use
of HTTP pipelining for any monitoring that takes place outside of the
endpoint or proxy solution. Since HTTP pipelining is between a
client and server, logging capabilities may require improvement in
some servers and clients for debugging purposes if this is not
already possible. Visibility for middleboxes includes anything
exposed by TLS and the 5-tuple.
4.1.3.3. HTTP Service Calls
When an application server makes an HTTP service call to back-end
services on behalf of a user session, it uses a completely different
URL and a completely different TCP connection. Troubleshooting via
network trace involves matching up the user request with the HTTP
service call. Some organizations do this today by decrypting the TLS
packet and inspecting the payload. Logging has not been adequate for
their purposes.
4.1.3.4. Application-Layer Data
Many applications use text formats such as XML to transport data or
application-level information. When transaction failures occur and
the logs are inadequate to determine the cause, network and
application teams work together, each having a different view of the
transaction failure. Using this troubleshooting method, the network
packet is correlated with the actual problem experienced by an
application to find a root cause. The inability to access the
payload prevents this method of troubleshooting.
4.2. Techniques for Monitoring Internet-Session Traffic
Corporate networks commonly monitor outbound session traffic to
detect or prevent attacks as well as to guarantee service-level
expectations. In some cases, alternate options are available when
encryption is in use through a proxy or a shift to monitoring at the
endpoint. In both cases, scaling is a concern, and advancements to
support this shift in monitoring practices will assist the deployment
of end-to-end encryption.
Some DLP tools intercept traffic at the Internet gateway or proxy
services with the ability to MITM encrypted session traffic (HTTP/
TLS). These tools may monitor for key words important to the
enterprise including business-sensitive information such as trade
secrets, financial data, PII, or PHI. Various techniques are used to
intercept HTTP/TLS sessions for DLP and other purposes and can be
misused as described in "Summarizing Known Attacks on Transport Layer
Security (TLS) and Datagram TLS (DTLS)" [RFC7457] (see Section 2.8).
Note: many corporate policies allow access to personal financial and
other sites for users without interception. Another option is to
terminate a TLS session prior to the point where monitoring is
performed. Aside from exposing user information to the enterprise,
MITM devices often are subject to severe security defects, which can
lead to exposure of user data to attackers outside the enterprise
user data [UserData]. In addition, implementation errors in
middleboxes have led to major difficulties in deploying new versions
of security protocols such as TLS [Ben17a] [Ben17b] [Res17a]
[Res17b].
Monitoring traffic patterns for anomalous behavior such as increased
flows of traffic that could be bursty at odd times or flows to
unusual destinations (small or large amounts of traffic) is common.
This traffic may or may not be encrypted, and various methods of
encryption or just obfuscation may be used.
Web-filtering devices are sometimes used to allow only access to
well-known sites found to be legitimate and free of malware on last
check by a web-filtering service company. One common example of web
filtering in a corporate environment is blocking access to sites that
are not well known to these tools for the purpose of blocking
malware; this may be noticeable to those in research who are unable
to access colleagues' individual sites or new websites that have not
yet been screened. In situations where new sites are required for
access, they can typically be added after notification by the user or
log alerts and review. Account access for personal mail may be
blocked in corporate settings to prevent another vector for malware
from entering as well as to prevent intellectual property leaks out
of the network. This method remains functional with increased use of
encryption and may be more effective at preventing malware from
entering the network. Some enterprises may be more aggressive in
their filtering and monitoring policy, causing undesirable outcomes.
Web-filtering solutions monitor and potentially restrict access based
on the destination URL (when available), server name, IP address, or
DNS name. A complete URL may be used in cases where access
restrictions vary for content on a particular site or for the sites
hosted on a particular server. In some cases, the enterprise may use
a proxy to access this additional information based on their policy.
This type of restriction is intended to be transparent to users in a
corporate setting as the typical corporate user does not access sites
that are not well known to these tools. However, the mechanisms that
these web filters use to do monitoring and enforcement have the
potential to cause access issues or other user-visible failures.
Desktop DLP tools are used in some corporate environments as well.
Since these tools reside on the desktop, they can intercept traffic
before it is encrypted and may provide a continued method for
monitoring leakage of intellectual property from the desktop to the
Internet or attached devices.
DLP tools can also be deployed by network service providers, as they
have the vantage point of monitoring all traffic paired with
destinations off the enterprise network. This makes an effective
solution for enterprises that allow "bring-your-own" devices when the
traffic is not encrypted and for devices outside the desktop category
(such as mobile phones) that are used on corporate networks
nonetheless.
Enterprises may wish to reduce the traffic on their Internet access
facilities by monitoring requests for within-policy content and
caching it. In this case, repeated requests for Internet content
spawned by URLs in email trade newsletters or other sources can be
served within the enterprise network. Gradual deployment of end-to-
end encryption would tend to reduce the cacheable content over time,
owing to concealment of critical headers and payloads. Many forms of
enterprise-performance management may be similarly affected. It
should be noted that transparent caching is considered an anti-
pattern.
5. Security Monitoring for Specific Attack Types
Effective incident response today requires collaboration at Internet
scale. This section will only focus on efforts of collaboration at
Internet scale that are dedicated to specific attack types. They may
require new monitoring and detection techniques in an increasingly
encrypted Internet. As mentioned previously, some service providers
have been interfering with STARTTLS to prevent session encryption to
be able to perform functions they are used to (injecting ads,
monitoring, etc.). By detailing the current monitoring methods used
for attack detection and response, this information can be used to
devise new monitoring methods that will be effective in the changed
Internet via collaboration and innovation.
Changes to improve encryption or to deploy OS methods have little
impact on the detection of malicious actors. Malicious actors have
had access to strong encryption for quite some time. Incident
responders, in many cases, have developed techniques to locate
malicious traffic within encrypted sessions. The following section
will note some examples where detection and mitigation of such
traffic has been successful.
5.1. Mail Abuse and Spam
The largest operational effort to prevent mail abuse is through the
Messaging, Malware, Mobile Anti-Abuse Working Group (M3AAWG)
[M3AAWG]. Mail abuse is combatted directly with mail administrators
who can shut down or stop continued mail abuse originating from
large-scale providers that participate in using the Abuse Reporting
Format (ARF) agents standardized in the IETF [RFC5965] [RFC6430]
[RFC6590] [RFC6591] [RFC6650] [RFC6651] [RFC6652]. The ARF agent
directly reports abuse messages to the appropriate service provider
who can take action to stop or mitigate the abuse. Since this
technique uses the actual message, the use of SMTP over TLS between
mail gateways will not affect its usefulness. As mentioned
previously, SMTP over TLS only protects data while in transit, and
the messages may be exposed on mail servers or mail gateways if a
user-to-user encryption method is not used. Current user-to-user
message encryption methods on email (S/MIME and PGP) do not encrypt
the email header information used by ARF and the service provider
operators in their efforts to mitigate abuse.
Another effort, "Domain-based Message Authentication, Reporting, and
Conformance (DMARC)" [RFC7489], is a mechanism for policy
distribution that enables increasingly strict handling of messages
that fail authentication checks, ranging from no action, through
altered delivery, up to message rejection. DMARC is also not
affected by the use of STARTTLS.
5.2. Denial of Service
Responses to Denial-of-Service (DoS) attacks are typically
coordinated by the service provider community with a few key vendors
who have tools to assist in the mitigation efforts. Traffic patterns
are determined from each DoS attack to stop or rate limit the traffic
flows with patterns unique to that DoS attack.
Data types used in monitoring traffic for DDoS are described in the
documents in development by the DDoS Open Threat Signaling (DOTS)
[DOTS] Working Group. The impact of encryption can be understood
from their documented use cases [DDOS-USECASE].
Data types used in DDoS attacks have been detailed in the Incident
Object Description Exchange Format (IODEF) Guidance document (see
[RFC8274], Appendix B.2) with the help of several members of the
service provider community. The examples provided are intended to
help identify the useful data in detecting and mitigating these
attacks independent of the transport and protocol descriptions in the
documents.
5.3. Phishing
Investigations and responses to phishing attacks follow well-known
patterns, requiring access to specific fields in email headers as
well as content from the body of the message. When reporting
phishing attacks, the recipient has access to each field as well as
the body to make content reporting possible, even when end-to-end
encryption is used. The email header information is useful to
identify the mail servers and accounts used to generate or relay the
attack messages in order to take the appropriate actions. The
content of the message often includes an embedded attack that may be
in an infected file or may be a link that results in the download of
malware to the user's system.
Administrators often find it helpful to use header information to
track down similar messages in their mail queue or in users' inboxes
to prevent further infection. Combinations of To:, From:, Subject:,
and Received: from header information might be used for this purpose.
Administrators may also search for document attachments of the same
name or size or that contain a file with a matching hash to a known
phishing attack. Administrators might also add URLs contained in
messages to block lists locally, or this may also be done by browser
vendors through larger-scale efforts like that of the Anti-Phishing
Working Group (APWG). See "Coordinating Attack Response at Internet
Scale (CARIS) Workshop Report" [RFC8073] for additional information
and pointers to the APWG's efforts on anti-phishing.
A full list of the fields used in phishing attack incident responses
can be found in RFC 5901. Future plans to increase privacy
protections may limit some of these capabilities if some email header
fields are encrypted, such as the To:, From:, and Subject: header
fields. This does not mean that those fields should not be
encrypted, only that we should be aware of how they are currently
used.
Some products protect users from phishing by maintaining lists of
known phishing domains (such as misspelled bank names) and blocking
access. This can be done by observing DNS, cleartext HTTP, or Server
Name Indication (SNI) in TLS, in addition to analyzing email.
Alternate options to detect and prevent phishing attacks may be
needed. More recent examples of data exchanged in spear phishing
attacks has been detailed in the IODEF Guidance document (see
[RFC8274], Appendix B.3).
5.4. Botnets
Botnet detection and mitigation is complex as botnets may involve
hundreds or thousands of hosts with numerous C&C servers. The
techniques and data used to monitor and detect each may vary.
Connections to C&C servers are typically encrypted; therefore, a move
to an increasingly encrypted Internet may not affect the detection
and sharing methods used.
5.5. Malware
Techniques for the detection and monitoring of malware vary. As
mentioned in Section 4, malware monitoring may occur at gateways to
the organization analyzing email and web traffic. These services can
also be provided by service providers, changing the scale and
location of this type of monitoring. Additionally, incident
responders may identify attributes unique to types of malware to help
track down instances by their communication patterns on the Internet
or by alterations to hosts and servers.
Data types used in malware investigations have been summarized in an
example of the IODEF Guidance document (see [RFC8274], Appendix B.3).
5.6. Spoofed-Source IP Address Protection
The IETF has reacted to spoofed-source IP address-based attacks,
recommending the use of network ingress filtering in BCP 38 [RFC2827]
and of the unicast Reverse Path Forwarding (uRPF) mechanism
[RFC3704]. But uRPF suffers from limitations regarding its
granularity: a malicious node can still use a spoofed IP address
included inside the prefix assigned to its link. Source Address
Validation Improvement (SAVI) mechanisms try to solve this issue.
Basically, a SAVI mechanism is based on the monitoring of a specific
address assignment/management protocol (e.g., Stateless Address
Autoconfiguration (SLAAC) [RFC4862], Secure Neighbor Discovery (SEND)
[RFC3971], and DHCPv4/v6 [RFC2131][RFC3315]) and, according to this
monitoring, sets up a filtering policy allowing only the IP flows
with a correct source IP address (i.e., any packet with a source IP
address from a node not owning it is dropped). The encryption of
parts of the address assignment/management protocols, critical for
SAVI mechanisms, can result in a dysfunction of the SAVI mechanisms.
5.7. Further Work
Although incident response work will continue, new methods to prevent
system compromise through security automation and continuous
monitoring [SACM] may provide alternate approaches where system
security is maintained as a preventative measure.
6. Application-Based Flow Information Visible to a Network
This section describes specific techniques used in monitoring
applications that are visible to the network if a 5-tuple is exposed
and as such can potentially be used as input for future network-
management approaches. It also includes an overview of IP Flow
Information Export (IPFIX), a flow-based protocol used to export
information about network flows.
6.1. IP Flow Information Export
Many of the accounting, monitoring, and measurement tasks described
in this document, especially in Sections 2.3.2, 3.1.1, 4.1.3, 4.2,
and 5.2, use the IPFIX protocol [RFC7011] for export and storage of
the monitored information. IPFIX evolved from the widely deployed
NetFlow protocol [RFC3954], which exports information about flows
identified by 5-tuple. While NetFlow was largely concerned with
exporting per-flow byte and packet counts for accounting purposes,
IPFIX's extensible Information Model [RFC7012] provides a variety of
Information Elements (IEs) [IPFIX-IANA] for representing information
above and below the traditional network-layer flow information.
Enterprise-specific IEs allow exporter vendors to define their own
non-standard IEs as well, and many of these are driven by header and
payload inspection at the Metering Process.
While the deployment of encryption has no direct effect on the use of
IPFIX, certain defined IEs may become unavailable when the Metering
Process observing the traffic cannot decrypt former cleartext
information. For example, HTTPS renders HTTP header analysis
impossible, so IEs derived from the header (e.g., httpContentType,
httpUserAgent) cannot be exported.
The collection of IPFIX data itself, of course, provides a point of
centralization for information that is potentially business and
privacy critical. The IPFIX File Format specification [RFC5655]
recommends encryption for this data at rest, and the IP Flow
Anonymization specification [RFC6235] defines a metadata format for
describing the anonymization functions applied to an IPFIX dataset,
if anonymization is employed for data sharing of IPFIX information
between enterprises or network operators.
6.2. TLS Server Name Indication
When initiating the TLS handshake, the client may provide an
extension field (server_name) that indicates the server to which it
is attempting a secure connection. TLS SNI was standardized in 2003
to enable servers to present the "correct TLS certificate" to clients
in a deployment of multiple virtual servers hosted by the same server
infrastructure and IP address. Although this is an optional
extension, it is today supported by all modern browsers, web servers,
and developer libraries. Akamai [Nygren] reports that many of their
customers see client TLS SNI usage over 99%. It should be noted that
HTTP/2 introduces the Alt-SVC method for upgrading the connection
from HTTP/1 to either unencrypted or encrypted HTTP/2. If the
initial HTTP/1 request is unencrypted, the destination alternate
service name can be identified before the communication is
potentially upgraded to encrypted HTTP/2 transport. HTTP/2 requires
the TLS implementation to support the SNI extension (see Section 9.2
of [RFC7540]). It is also worth noting that [RFC7838] "allows an
origin server to nominate additional means of interacting with it on
the network", while [RFC8164] allows for a URI to be accessed with
HTTP/2 and TLS using Opportunistic Security (on an experimental
basis).
This information is only available if the client populates the SNI
extension. Doing so is an optional part of the TLS standard, and as
stated above, this has been implemented by all major browsers. Due
to its optional nature, though, existing network filters that examine
a TLS ClientHello for an SNI extension cannot expect to always find
one. "SNI Encryption in TLS Through Tunneling" [SNI-TLS] has been
adopted by the TLS Working Group, which provides solutions to encrypt
SNI. As such, there will be an option to encrypt SNI in future
versions of TLS. The per-domain nature of SNI may not reveal the
specific service or media type being accessed, especially where the
domain is of a provider offering a range of email, video, web pages,
etc. For example, certain blog or social network feeds may be deemed
"adult content", but the SNI will only indicate the server domain
rather than a URL path.
There are additional issues for identification of content using SNI:
[RFC7540] includes connection coalescing, [RFC8336] defines the
ORIGIN frame, and the proposal outlined in [HTTP2-CERTS] will
increase the difficulty of passive monitoring.
6.3. Application-Layer Protocol Negotiation (ALPN)
ALPN is a TLS extension that may be used to indicate the application
protocol within the TLS session. This is likely to be of more value
to the network where it indicates a protocol dedicated to a
particular traffic type (such as video streaming) rather than a
multi-use protocol. ALPN is used as part of HTTP/2 'h2', but will
not indicate the traffic types that may make up streams within an
HTTP/2 multiplex. ALPN is sent cleartext in the ClientHello, and the
server returns it in Encrypted Extensions in TLS 1.3.
6.4. Content Length, Bitrate, and Pacing
The content length of encrypted traffic is effectively the same as
that of the cleartext. Although block ciphers utilize padding, this
makes a negligible difference. Bitrate and pacing are generally
application specific and do not change much when the content is
encrypted. Multiplexed formats (such as HTTP/2 and QUIC [QUIC]) may,
however, incorporate several application streams over one connection,
which makes the bitrate/pacing no longer application specific. Also,
packet padding is available in HTTP/2, TLS 1.3, and many other
protocols. Traffic analysis is made more difficult by such
countermeasures.
7. Effect of Encryption on the Evolution of Mobile Networks
Transport header encryption prevents the use of transit proxies in
the center of the network and the use of some edge proxies by
preventing the proxies from taking action on the stream. It may be
that the claimed benefits of such proxies could be achieved by
end-to-end client and server optimizations, distribution using CDNs,
plus the ability to continue connections across different access
technologies (across dynamic user IP addresses). The following
aspects should be considered in this approach:
1. In a wireless mobile network, the delay and channel capacity per
user and sector varies due to coverage, contention, user
mobility, scheduling balances fairness, capacity, and service
QoE. If most users are at the cell edge, the controller cannot
use more-complex Quadrature Amplitude Modulation (QAM), thus
reducing total cell capacity; similarly, if a Universal Mobile
Telecommunications System (UMTS) edge is serving some number of
CS-Voice Calls, the remaining capacity for packet services is
reduced.
2. Mobile wireless networks service inbound roamers (users of
Operator A in the foreign network of Operator B) by backhauling
their traffic through the network (from Operator B to Operator A)
and then serving them through the P-Gateway (PGW), General Packet
Radio Service (GPRS) Support Node (GGSN), CDN, etc., of Operator
A (the user's home operator). Increasing window sizes to
compensate for the path RTT will have the limitations outlined
earlier for TCP. The outbound roamer scenario has a similar TCP
performance impact.
3. Issues in deploying CDNs in Radio Access Networks (RANs) include
decreasing the client-server control loop that requires deploying
CDNs / Cloud functions that terminate encryption closer to the
edge. In Cellular RAN, the user IP traffic is encapsulated into
GPRS Tunneling Protocol-User Plane (GTP-U in UMTS and LTE)
tunnels to handle user mobility; the tunnels terminate in
APN/GGSN/PGW that are in central locations. One user's traffic
may flow through one or more APN's (for example, Internet APN,
Roaming APN for Operator X, Video-Service APN, OnDeckAPN, etc.).
The scope of operator private IP addresses may be limited to
specific APNs. Since CDNs generally operate on user IP flows,
deploying them would require enhancing them with tunnel
translation, tunnel-management functions, etc.
4. While CDNs that decrypt flows or split connection proxies
(similar to split TCP) could be deployed closer to the edges to
reduce control-loop RTT, with transport header encryption, such
CDNs perform optimization functions only for partner client
flows. Therefore, content from some Small-Medium Businesses
(SMBs) would not get such CDN benefits.
8. Response to Increased Encryption and Looking Forward
As stated in [RFC7258], "an appropriate balance [between network
management and pervasive monitoring mitigations] will emerge over
time as real instances of this tension are considered." Numerous
operators made it clear in their response to this document that they
fully support strong encryption and providing privacy for end users;
this is a common goal. Operators recognize that not all the
practices documented need to be supported going forward, either
because of the risk to end-user privacy or because alternate
technologies and tools have already emerged. This document is
intended to support network engineers and other innovators to work
toward solving network and security management problems with protocol
designers and application developers in new ways that facilitate
adoption of strong encryption rather than preventing the use of
encryption. By having the discussions on network and security
management practices with application developers and protocol
designers, each side of the debate can understand each other's goals,
work toward alternate solutions, and disband with practices that
should no longer be supported. A goal of this document is to assist
the IETF in understanding some of the current practices so as to
identify new work items for IETF-related use cases that can
facilitate the adoption of strong session encryption and support
network and security management.
9. Security Considerations
There are no additional security considerations as this is a summary
and does not include a new protocol or functionality.
10. IANA Considerations
This document has no IANA actions.
11. Informative References
[ACCORD] IETF, "Alternatives to Content Classification for Operator
Resource Deployment (accord) (BOF)", IETF-95 Proceedings,
April 2016,
<https://www.ietf.org/proceedings/95/accord.html>.
[Ben17a] Benjamin, D., "Chrome Data", Presentation before the TLS
WG at IETF 100, November 2017,
<https://datatracker.ietf.org/meeting/100/materials/
slides-100-tls-sessa-tls13/>.
[Ben17b] Benjamin, D., "Subject: Additional TLS 1.3 results from
Chrome", message to the TLS mailing list, 18 December
2017, <https://www.ietf.org/mail-archive/web/tls/current/
msg25168.html>.
[CAIDA] CAIDA, "The CAIDA USCD Anonymized Internet Traces 2016
Dataset", <http://www.caida.org/data/passive/
passive_2016_dataset.xml>.
[DarkMail] "Dark Mail Technical Alliance", <https://darkmail.info/>.
[DDOS-USECASE]
Dobbins, R., Migault, D., Fouant, S., Moskowitz, R.,
Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS
Open Threat Signaling", Work in Progress, draft-ietf-dots-
use-cases-16, July 2018.
[DOTS] IETF, "DDoS Open Threat Signaling (dots)",
<https://datatracker.ietf.org/wg/dots/charter>.
[EFF2014] Hoffman-Andrews, J., "ISPs Removing Their Customers' Email
Encryption", November 2014,
<https://www.eff.org/deeplinks/2014/11/
starttls-downgrade-attacks>.
[Enrich] Narseo Vallina-Rodriguez, N., Sundaresan, S., Kreibich,
C., and V. Paxson, "Header Enrichment or ISP Enrichment:
Emerging Privacy Threats in Mobile Networks", Proceedings
of the ACM SIGCOMM Workshop on Hot Topics in Middleboxes
and Network Function Virtualization, pp. 23-30,
DOI 10.1145/2785989.2786002, August 2015.
[GENEVE-REQS]
Migault, D., Boutros, S., Wing, D., and S. Krishnan,
"Geneve Protocol Security Requirements", Work in
Progress, draft-mglt-nvo3-geneve-security-requirements-03,
February 2018.
[HTTP2-CERTS]
Bishop, M., Sullivan, N., and M. Thomson, "Secondary
Certificate Authentication in HTTP/2", Work in Progress,
draft-ietf-httpbis-http2-secondary-certs-02, June 2018.
[IPFIX-IANA]
IANA, "IP Flow Information Export (IPFIX) Entities",
<https://www.iana.org/assignments/ipfix/>.
[JNSLP] Eskens, S., "10 Standards for Oversight and Transparency
of National Intelligence Services", Surveillance, Vol. 8,
No. 3, July 2016, <http://jnslp.com/?s=10+Standards+for+Ov
ersight+and+Transparency+of+National>.
[M3AAWG] M3AAWG, "Messaging, Malware and Mobile Anti-Abuse Working
Group (M3AAWG)", <https://www.maawg.org/>.
[MIDDLEBOXES]
Dolson, D., Snellman, J., Boucadair, M., and C. Jacquenet,
"An Inventory of Transport-centric Functions Provided by
Middleboxes", Work in Progress, draft-dolson-transport-
middlebox-03, June 2018.
[Nygren] Nygren, E., "Reaching toward Universal TLS SNI",
Akamai Technologies, March 2017,
<https://blogs.akamai.com/2017/03/
reaching-toward-universal-tls-sni.html>.
[QUIC] IETF, "QUIC (quic)",
<https://datatracker.ietf.org/wg/quic/charter/>.
[Res17a] Rescorla, E., "Subject: Preliminary data on Firefox TLS
1.3 Middlebox experiment", message to the TLS mailing
list, 5 December 2017, <https://www.ietf.org/mail-archive/
web/tls/current/msg25091.html>.
[Res17b] Rescorla, E., "Subject: More compatibility measurement
results", message to the TLS mailing list, 22 December
2017, <https://www.ietf.org/mail-archive/web/tls/current/
msg25179.html>.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945,
DOI 10.17487/RFC1945, May 1996,
<https://www.rfc-editor.org/info/rfc1945>.
[RFC1958] Carpenter, B., Ed., "Architectural Principles of the
Internet", RFC 1958, DOI 10.17487/RFC1958, June 1996,
<https://www.rfc-editor.org/info/rfc1958>.
[RFC1984] IAB and IESG, "IAB and IESG Statement on Cryptographic
Technology and the Internet", BCP 200, RFC 1984,
DOI 10.17487/RFC1984, August 1996,
<https://www.rfc-editor.org/info/rfc1984>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, DOI 10.17487/RFC2663, August 1999,
<https://www.rfc-editor.org/info/rfc2663>.
[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775,
DOI 10.17487/RFC2775, February 2000,
<https://www.rfc-editor.org/info/rfc2775>.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
DOI 10.17487/RFC2804, May 2000,
<https://www.rfc-editor.org/info/rfc2804>.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135,
DOI 10.17487/RFC3135, June 2001,
<https://www.rfc-editor.org/info/rfc3135>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
2004, <https://www.rfc-editor.org/info/rfc3704>.
[RFC3724] Kempf, J., Ed., Austein, R., Ed., and IAB, "The Rise of
the Middle and the Future of End-to-End: Reflections on
the Evolution of the Internet Architecture", RFC 3724,
DOI 10.17487/RFC3724, March 2004,
<https://www.rfc-editor.org/info/rfc3724>.
[RFC3954] Claise, B., Ed., "Cisco Systems NetFlow Services Export
Version 9", RFC 3954, DOI 10.17487/RFC3954, October 2004,
<https://www.rfc-editor.org/info/rfc3954>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address
Translation (NAT) Behavioral Requirements for Unicast
UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
2007, <https://www.rfc-editor.org/info/rfc4787>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC5655] Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
Wagner, "Specification of the IP Flow Information Export
(IPFIX) File Format", RFC 5655, DOI 10.17487/RFC5655,
October 2009, <https://www.rfc-editor.org/info/rfc5655>.
[RFC5965] Shafranovich, Y., Levine, J., and M. Kucherawy, "An
Extensible Format for Email Feedback Reports", RFC 5965,
DOI 10.17487/RFC5965, August 2010,
<https://www.rfc-editor.org/info/rfc5965>.
[RFC6108] Chung, C., Kasyanov, A., Livingood, J., Mody, N., and B.
Van Lieu, "Comcast's Web Notification System Design",
RFC 6108, DOI 10.17487/RFC6108, February 2011,
<https://www.rfc-editor.org/info/rfc6108>.
[RFC6235] Boschi, E. and B. Trammell, "IP Flow Anonymization
Support", RFC 6235, DOI 10.17487/RFC6235, May 2011,
<https://www.rfc-editor.org/info/rfc6235>.
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
P. Roberts, "Issues with IP Address Sharing", RFC 6269,
DOI 10.17487/RFC6269, June 2011,
<https://www.rfc-editor.org/info/rfc6269>.
[RFC6430] Li, K. and B. Leiba, "Email Feedback Report Type Value:
not-spam", RFC 6430, DOI 10.17487/RFC6430, November 2011,
<https://www.rfc-editor.org/info/rfc6430>.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/info/rfc6455>.
[RFC6590] Falk, J., Ed. and M. Kucherawy, Ed., "Redaction of
Potentially Sensitive Data from Mail Abuse Reports",
RFC 6590, DOI 10.17487/RFC6590, April 2012,
<https://www.rfc-editor.org/info/rfc6590>.
[RFC6591] Fontana, H., "Authentication Failure Reporting Using the
Abuse Reporting Format", RFC 6591, DOI 10.17487/RFC6591,
April 2012, <https://www.rfc-editor.org/info/rfc6591>.
[RFC6650] Falk, J. and M. Kucherawy, Ed., "Creation and Use of Email
Feedback Reports: An Applicability Statement for the Abuse
Reporting Format (ARF)", RFC 6650, DOI 10.17487/RFC6650,
June 2012, <https://www.rfc-editor.org/info/rfc6650>.
[RFC6651] Kucherawy, M., "Extensions to DomainKeys Identified Mail
(DKIM) for Failure Reporting", RFC 6651,
DOI 10.17487/RFC6651, June 2012,
<https://www.rfc-editor.org/info/rfc6651>.
[RFC6652] Kitterman, S., "Sender Policy Framework (SPF)
Authentication Failure Reporting Using the Abuse Reporting
Format", RFC 6652, DOI 10.17487/RFC6652, June 2012,
<https://www.rfc-editor.org/info/rfc6652>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7012] Claise, B., Ed. and B. Trammell, Ed., "Information Model
for IP Flow Information Export (IPFIX)", RFC 7012,
DOI 10.17487/RFC7012, September 2013,
<https://www.rfc-editor.org/info/rfc7012>.
[RFC7143] Chadalapaka, M., Satran, J., Meth, K., and D. Black,
"Internet Small Computer System Interface (iSCSI) Protocol
(Consolidated)", RFC 7143, DOI 10.17487/RFC7143, April
2014, <https://www.rfc-editor.org/info/rfc7143>.
[RFC7146] Black, D. and P. Koning, "Securing Block Storage Protocols
over IP: RFC 3723 Requirements Update for IPsec v3",
RFC 7146, DOI 10.17487/RFC7146, April 2014,
<https://www.rfc-editor.org/info/rfc7146>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>.
[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>.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
<https://www.rfc-editor.org/info/rfc7348>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>.
[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
February 2015, <https://www.rfc-editor.org/info/rfc7457>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>.
[RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
Service Function Chaining", RFC 7498,
DOI 10.17487/RFC7498, April 2015,
<https://www.rfc-editor.org/info/rfc7498>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[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>.
[RFC7619] Smyslov, V. and P. Wouters, "The NULL Authentication
Method in the Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 7619, DOI 10.17487/RFC7619, August 2015,
<https://www.rfc-editor.org/info/rfc7619>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015,
<https://www.rfc-editor.org/info/rfc7624>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC7754] Barnes, R., Cooper, A., Kolkman, O., Thaler, D., and E.
Nordmark, "Technical Considerations for Internet Service
Blocking and Filtering", RFC 7754, DOI 10.17487/RFC7754,
March 2016, <https://www.rfc-editor.org/info/rfc7754>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC7826] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
and M. Stiemerling, Ed., "Real-Time Streaming Protocol
Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
2016, <https://www.rfc-editor.org/info/rfc7826>.
[RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
April 2016, <https://www.rfc-editor.org/info/rfc7838>.
[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>.
[RFC8073] Moriarty, K. and M. Ford, "Coordinating Attack Response at
Internet Scale (CARIS) Workshop Report", RFC 8073,
DOI 10.17487/RFC8073, March 2017,
<https://www.rfc-editor.org/info/rfc8073>.
[RFC8164] Nottingham, M. and M. Thomson, "Opportunistic Security for
HTTP/2", RFC 8164, DOI 10.17487/RFC8164, May 2017,
<https://www.rfc-editor.org/info/rfc8164>.
[RFC8165] Hardie, T., "Design Considerations for Metadata
Insertion", RFC 8165, DOI 10.17487/RFC8165, May 2017,
<https://www.rfc-editor.org/info/rfc8165>.
[RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6
Performance and Diagnostic Metrics (PDM) Destination
Option", RFC 8250, DOI 10.17487/RFC8250, September 2017,
<https://www.rfc-editor.org/info/rfc8250>.
[RFC8274] Kampanakis, P. and M. Suzuki, "Incident Object Description
Exchange Format Usage Guidance", RFC 8274,
DOI 10.17487/RFC8274, November 2017,
<https://www.rfc-editor.org/info/rfc8274>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8336] Nottingham, M. and E. Nygren, "The ORIGIN HTTP/2 Frame",
RFC 8336, DOI 10.17487/RFC8336, March 2018,
<https://www.rfc-editor.org/info/rfc8336>.
[SACM] IETF, "Security Automation and Continuous Monitoring
(sacm)", <https://datatracker.ietf.org/wg/sacm/charter/>.
[SNI-TLS] Huitema, C. and E. Rescorla, "Issues and Requirements for
SNI Encryption in TLS", Work in Progress, draft-ietf-tls-
sni-encryption-03, May 2018.
[Snowden] Verble, J., "The NSA and Edward Snowden: Surveillance in
the 21st Century", SIGCAS Computer & Society, Vol. 44,
No. 3, DOI 10.1145/2684097.2684101, September 2014,
<http://www.jjsylvia.com/bigdatacourse/wp-content/
uploads/2016/04/p14-verble-1.pdf>.
[TCPcrypt]
IETF, "TCP Increased Security (tcpinc)",
<https://datatracker.ietf.org/wg/tcpinc/charter>.
[TS3GPP] 3GPP, "Non-Access-Stratum (NAS) protocol for Evolved
Packet System (EPS); Stage 3", 3GPP TS 24.301, version
15.2.0, March 2018.
[UPCON] 3GPP, "User Plane Congestion Management", 3GPP Rel-13,
September 2014, <http://www.3gpp.org/DynaReport/
FeatureOrStudyItemFile-570029.htm>.
[UserData]
Durumeric, Z., Ma, Z., Springall, D., Barnes, R.,
Sullivan, N., Bursztein, E., Bailey, M., Alex Halderman,
J., and V. Paxson, "The Security Impact of HTTPS
Interception", Network and Distributed Systems Symposium,
February 2017,
<http://dx.doi.org/10.14722/ndss.2017.23456>.
Acknowledgements
Thanks to our reviewers, Natasha Rooney, Kevin Smith, Ashutosh Dutta,
Brandon Williams, Jean-Michel Combes, Nalini Elkins, Paul Barrett,
Badri Subramanyan, Igor Lubashev, Suresh Krishnan, Dave Dolson,
Mohamed Boucadair, Stephen Farrell, Warren Kumari, Alia Atlas, Roman
Danyliw, Mirja Kuehlewind, Ines Robles, Joe Clarke, Kyle Rose,
Christian Huitema, and Chris Morrow for their editorial and content
suggestions. Surya K. Kovvali provided material for Section 7.
Chris Morrow and Nik Teague provided reviews and updates specific to
the DoS fingerprinting text. Brian Trammell provided the IPFIX text.
Authors' Addresses
Kathleen Moriarty (editor)
Dell EMC
176 South St
Hopkinton, MA
United States of America
Email: Kathleen.Moriarty@dell.com
Al Morton (editor)
AT&T Labs
200 Laurel Avenue South
Middletown, NJ 07748
United States of America
Phone: +1 732 420 1571
Fax: +1 732 368 1192
Email: acm@research.att.com