Internet DRAFT - draft-camwinget-opsec-ns-impact
draft-camwinget-opsec-ns-impact
OPSEC Working Group N. Cam-Winget
Internet-Draft E. Wang
Intended status: Informational Cisco Systems, Inc.
Expires: November 29, 2020 R. Danyliw
Software Engineering Institute
R. DuToit
Broadcom
May 28, 2020
Impact of TLS 1.3 to Operational Network Security Practices
draft-camwinget-opsec-ns-impact-00
Abstract
Network-based security solutions are used by enterprises, the public
sector, internet-service providers, and cloud-service providers to
both complement and enhance host-based security solutions. As TLS is
a widely deployed protocol to secure communication, these network-
based security solutions must necessarily interact with it. This
document describes this interaction for current operational security
practices and notes the impact of TLS 1.3 on them.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 29, 2020.
Copyright Notice
Copyright (c) 2020 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. How TLS is used to enable Network-Based Security Solutions . 4
3.1. Passive TLS Inspection . . . . . . . . . . . . . . . . . 5
3.1.1. OP-1. Acceptable Use Policy (AUP) Enforcement (via
header inspection). . . . . . . . . . . . . . . . . . 6
3.1.2. OP-2. Network Behavior Analytics . . . . . . . . . . 6
3.1.3. OP-3. Crypto, Security and Security Policy
Compliance (server) . . . . . . . . . . . . . . . . . 7
3.1.4. OP-4. Crypto and Security Policy Compliance (client) 7
3.2. Outbound TLS Proxy . . . . . . . . . . . . . . . . . . . 8
3.2.1. OP-5: Acceptable Use Policy (AUP) Enforcement (via
payload inspection) . . . . . . . . . . . . . . . . . 9
3.2.2. OP-6: Data Loss Prevention Compliance . . . . . . . . 9
3.2.3. OP-7: Granular Network Segmentation . . . . . . . . . 9
3.2.4. OP-8: Network-based Threat Protection (client) . . . 9
3.2.5. OP-9: Protecting Challenging End Points . . . . . . . 10
3.2.6. OP-10: Content Injection . . . . . . . . . . . . . . 10
3.3. Inbound TLS Proxy . . . . . . . . . . . . . . . . . . . . 10
3.3.1. OP-11: TLS offloading . . . . . . . . . . . . . . . . 11
3.3.2. OP-12. Content distribution and application load
balancing . . . . . . . . . . . . . . . . . . . . . . 12
3.3.3. OP-13: Network-based Threat Protection (server) . . . 12
3.3.4. OP-14: Full Packet Capture . . . . . . . . . . . . . 12
3.3.5. OP-15: Application Layer Gateway (ALG) . . . . . . . 13
4. Changes in TLS v1.3 Relevant to Security Operations . . . . . 13
4.1. Perfect Forward Secrecy (PFS) . . . . . . . . . . . . . . 13
4.2. Encrypted Server Certificate . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Appendix A: Summary Impact to Operational Practices with TLS
1.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 16
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
Enterprises, public sector organizations, internet service providers
and cloud service providers defend their networks and information
systems from attacks that originate from inside and outside their
networks. These organizations commonly employ security architectures
that involve complementary technologies deployed on both endpoints
and in the network; and collaborative watch-and-warning practices to
realize this defense.
The design of these security architectures and associated practices
entails numerous trade-offs. Typically, there is more than one
technical approach to realize a particular mitigation, although
comparable approaches may have different costs or side-effects.
Network-based solutions are often attractive to network
administrators because a single network device can:
o provide protection to many hosts and systems at once
o protect systems regardless of their type (e.g., fully patched
desktop systems on a modern operating system; unpatched function-
specific industrial control system)
o enforce policy on a system even if it is compromised,
misconfigured, not under configuration control or had its endpoint
protection disabled
o be managed (e.g. updates) and provisioned with resources (e.g.
disk and computing) independent of the systems it is protecting
In response to the adoption of new technologies, protocols and
threats, these security architectures must evolve to remain
effective. [RFC8404] documented such a need with the effect of
pervasive encryption on operations. This document takes a narrower
focus by documenting the interaction of existing network-based
security practices with TLS v1.2 [RFC5246] (and earlier) traffic to
implement security policy, detection or mitigation of threats; and
the impact on these practices with improvements made in TLS v1.3
[RFC8446].
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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Specific operational practices are numbered as "OP-##", operational
practice 1 (i.e., OP-1), 2 (i.e., OP-2), etc.
3. How TLS is used to enable Network-Based Security Solutions
Network-based security solutions come in many forms, most commonly as
Firewalls, Web Proxies, Intrusion Detection Systems (IDS), Intrusion
Prevention Systems (IPS) and Network Security Visibility and
Analytics systems. They inspect the network traffic, and then based
on their function, log their observation and/or act on the traffic to
implement security policy. When these devices act on the network
traffic, they are typically deployed inline as middleboxes (e.g.
firewalls) or as explicit proxies (e.g. web proxies). If their
function is only to observe, they can be deployed either as
middleboxes or given access to the network traffic out-of-band (OOB),
through the network fabric (e.g., network tap or span port).
Depending on their function, network-based security devices use
different degrees of visibility into the TLS traffic. Some
operational practices require only access to the unencrypted protocol
headers and associated meta-data of the TLS traffic. Other practices
require full visibility into the encrypted session (payload).
The practices that inspect only the unencrypted headers and meta-data
of TLS, require no special capabilities beyond access to the TLS
packets. However, to inspect the encrypted payload of TLS traffic
requires a TLS proxy.
A TLS proxy provides visibility and inspection to effectuate security
controls without changing the state machine of the TLS Server and TLS
Client, or the user experience. The TLS Proxy operates as a
transparent hop at the TLS layer in both middlebox and explicit proxy
deployments. For the web proxy case, after the client sends an HTTP
CONNECT to request a tunnel to the server, the web proxy may insert a
TLS Proxy function to proxy the TLS session without awareness by the
client or server. The TLS operation afterwards remains the same as a
middlebox.
To proxy a TLS session, a TLS Proxy must be able to present a valid
X.509 certificate to the TLS client to appear as a valid TLS Server;
similarly, the client must be able to validate the X.509 certificate
using the appropriate trust anchor for that TLS connection. To
achieve this, a deployment must properly provision their systems (TLS
Proxies and TLS clients).
Specific network security operational practices applied to TLS v1.2
(and earlier) are described in subsequent sub-sections. They are
categorized into the following deployment scenarios:
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1. Passive TLS inspection, where the network-based security function
is inspecting either the inbound or outbound TLS header or meta-
data traffic
2. Outbound TLS Proxy, where a TLS proxy mediates a TLS session
originating from a client inside the enterprise administrative
domain (and in the same administrative domain as the proxy)
towards an entity on the outside
3. Inbound TLS Proxy, where a TLS proxy mediates a TLS session from
a client outside the enterprise administrative domain towards an
entity on the inside (and in the same administrative domain as
the proxy)
Each deployment scenario describes relevant operational practices.
For each operational practice, possible deployment modes (e.g.,
inline, out-of-band), a description of the practice, and the impact
of TLS v1.3 is categorized and explained. The categorized impacts to
practices when migrating to TLS v1.3 are as follows:
o no impact - no change in capability or performance is expected
with this practice
o no capability impact - no change in capability is expected; but
there may be a performance or implementation change required for
this practice
o reduced effectiveness - this practice will not be as effective on
TLS v1.3 traffic
o alternative approach required - this practice will not work with
TLS v1.3 traffic
3.1. Passive TLS Inspection
Passive TLS inspection is the deployment scenario where a network
security device passively inspects inbound or outbound TLS traffic to
make visibility inferences or take policy actions. The network
security device examines only the unencrypted TLS protocol headers
and does not have access to the encrypted content of the payload.
The TLS proxy deployment scenarios may also incorporate these
practices.
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3.1.1. OP-1. Acceptable Use Policy (AUP) Enforcement (via header
inspection).
Deployment mode: inline
A firewall or web proxy restricts a client in the same administrative
domain from accessing sites or services outside that domain per an
acceptable use policy. The identification of the destination server
is performed through the inspection of either the SNI field in the
TLS ClientHello message from the client; or by extracting the server
identity from the Common Name (CN) or Subject Alternative Name (SAN)
fields of an X.509 certificate that is presented in the server's
Certificate TLS message. This data is used for domain categorization
or application identification.
This meta-data can also inform decryption eligibility decisions by a
firewall, in OP-4. For instance, a firewall may bypass traffic
decryption for a connection destined to a healthcare web service due
to privacy compliance requirements.
TLS 1.3 impact: reduced effectiveness. Per Section 4.2, domain
categorization and application identification will be limited to IP
address and SNI information (beyond additional correlation possible
with other means such as DNS).
While an SNI is mandatory in TLS 1.3, there is no guarantee that the
server responding is the one indicated in the SNI from the client. A
SNI alone, without comparison of the server certificate, does not
provide reliable information about the server that the client is
attempting to reach. Where a client has been compromised by malware,
it may present an innocuous SNI to bypass protective filters (e.g.,
to reach a command and control server), and this will be undetectable
under TLS 1.3.
[ESNI] will further reduce the effectiveness of passive TLS
inspection, limiting the available information to IP addresses and
possible correlation with DNS.
3.1.2. OP-2. Network Behavior Analytics
Deployment mode: inline and out-of-band
Network behavior analysis and machine learning engines in IDSs, IPSs
and firewalls observe the cleartext fields of the TLS handshake
(e.g., session cipher suites) and conducts traffic analysis by
observing encrypted record sizes, packet rates and their inter-
arrival times, and similar outer connection behavior. They match
encrypted connections against known application patterns; identify
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anomalies; and identify or block those without payload inspection.
These analytics may also observe that malicious applications may
deliberately manipulate certain TLS header fields, throttle packet
rates, and vary payload sizes in order to circumvent detection.
Through traffic analysis, researchers have detected devastating
pseudo-random number generator failures [TLS_VULNERABILITY], nonce
failures [NONCE_FAIL], and deeply flawed random number generators in
products in [WEAK_KEY] and [WEAK_K2].
TLS 1.3 considerations: reduced effectiveness. Per Section 4.2, any
features relying on Certificate information will not be available.
3.1.3. OP-3. Crypto, Security and Security Policy Compliance (server)
Deployment: out-of-band
A network security device observes TLS handshake traffic to audit
that TLS server configuration conforms to policy. This compliance
monitoring commonly examines ciphersuites (e.g., use of weak
ciphersuites) and certificate properties (e.g., no self-signed
certificates, black or white list of certificate authorities,
certificate expiration times).
TLS 1.3 considerations: reduced effectiveness. Per Section 4.2, only
TLS ClientHello and ServerHello parameters can be audited.
Certification information will not be visible.
3.1.4. OP-4. Crypto and Security Policy Compliance (client)
Deployment: inline
A network security device observes TLS handshake traffic to ensure
that clients negotiating TLS connections have configurations (e.g.,
only make connections with TLS 1.2+) and server certificate (e.g.,
black-listed CAs) that adhere to policy. This is a variant of OP-3.
It is commonly used in deployments where an organization may have
reduced configuration control of end points (e.g., lab environments,
Bring Your Own Device arrangements, and IoT).
TLS 1.3 considerations: reduced effectiveness. Per Section 4.2, only
TLS ClientHello and ServerHello parameters can be audited.
Certification information will not be visible.
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3.2. Outbound TLS Proxy
Outbound TLS proxy is the deployment scenario where a security device
that performs the TLS proxy function is in the same administrative
domain as the TLS client, and the TLS server is located in an
external zone such as the Internet or in another policy zone of the
same administrative domain. Usually the goal is to protect the
client endpoint and the organization by controlling application
behaviors and enforcing an acceptable use policy for the
organizational network. See Figure 1.
The administrator manages the TLS client to allow interception by the
TLS proxy, usually by deploying a local Certificate Authority (CA)
certificate on the TLS client. A typical scenario is an
organization-managed client endpoint, such as a laptop or a mobile
device that accesses the Internet through the organizational network.
When a client attempts to access an external TLS server, the TLS
proxy function typically presents a locally signed certificate from
the local CA on behalf of the server; alternatively, the certificate
generation function may be offloaded to an external Hardware Security
Module (HSM) service with which that the TLS proxy must integrate.
It has to be noted that the method does not work if the TLS client
does not support customized list of CAs, such as with certificate
pinning. The impact is independent of TLS 1.3 deployment.
_________ __________
\ /
\ | Administrative
\ | Domain, _----__
+-+ \ | Zone 2 / / \____
| | \ \______/ __/ +------+ \
|C|.. | . / |S-NEWS| \__
| | . | . ( +------+ \
+-+ . +---+ . ( +--------+ )
..| |.... \ |S-GAMING| )
| P |..........( +--------+ )
+-+ ...| | \ +---------+ )
| | . +---+ ( |S-BANKING| /
|C|... | \_.+---------+ )
| | | \.. /
+-+ / \____--'
/
Administrative / Internet
Domain, Zone 1 /
_________/
Figure 1: Outbound TLS proxy
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3.2.1. OP-5: Acceptable Use Policy (AUP) Enforcement (via payload
inspection)
Deployment: inline
A firewall or web proxy restricts a client in the same administrative
domain from accessing sites or services outside that domain per an
acceptable use policy. Similar in intent to OP-1, but the policy
enforcement in this practice requires access to data in the TLS
session (e.g., URL).
TLS 1.3 considerations: no capability impact. See Section 4.2 if a
selective decryption policy is used.
3.2.2. OP-6: Data Loss Prevention Compliance
Deployment: inline
A firewall enforces a Data Loss Prevention (DLP) policy by monitoring
the TLS sessions content of outbound communication for systems
sending organizational proprietary content or other restricted
information.
TLS 1.3 considerations: no capability impact. See Section 4.2 if a
selective decryption policy is used.
3.2.3. OP-7: Granular Network Segmentation
Deployment: inline
A firewall mediates the traffic between different policy zones in an
organization. The access policies between these zones may be based
on application names and categories rather than static IP addresses
and TCP/UDP port numbers. Through a TLS proxy, the firewall can
inspect URLs and other application parameters based on data in the
TLS session.
TLS 1.3 considerations: no capability impact. See Section 4.2 if a
selective decryption policy is used.
3.2.4. OP-8: Network-based Threat Protection (client)
Deployment: inline or out-of-band (depending on functionality)
Web proxies and firewalls protect end-users against a range of
threats by inspecting the data in the TLS session with a variety of
analytical techniques (e.g., signatures, heuristics, statistical
models, machine learning). This practice is a superset of OP-2.
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Common goals are to prevent malware from reaching the endpoint,
preventing malware communication from a compromised host, restricting
lateral network movement of an intruder and gathering insight into
the behavior of threat activity on the network.
In certain deployments these technologies are also used to act as a
last line of defense against software vulnerabilities on endpoints -
either for 0-days for which there is no patch, or simply unpatched
clients.
TLS 1.3 considerations: no capability impact. See Section 4.2 if a
selective decryption policy is used.
3.2.5. OP-9: Protecting Challenging End Points
Deployment mode: inline
Web proxies, IPS and firewalls implement security policy and afford
protection to devices for which it is not feasible to run an end-
point solution (e.g., IoT); or that are end-of-life and will not
receive patches. This is a specialized instance of OP-8 targeting
these disadvantaged classes of devices.
These practices ensure that that older endpoints (and in some cases
even new ones) are not permanently vulnerable to newly discovered
vulnerabilities.
TLS 1.3 considerations: no capability impact. See Section 4.2 if a
selective decryption policy is used.
3.2.6. OP-10: Content Injection
Deployment: inline
A firewall or web proxy restricts message manipulation or insertion,
such as a block page or an interactive authentication portal
redirect, into the encrypted flow for the client to see. This may be
used in conjunction with OP-1, OP-5, and OP-7.
TLS 1.3 considerations: no capability impact. See Section 4.2 if a
selective decryption policy is used.
3.3. Inbound TLS Proxy
Inbound TLS proxy is the deployment scenario where the TLS proxy is
deployed in front of one or a set of servers or services. The
network device that implements the TLS proxy function is located in
the same administrative domain as the server(s) or service(s) it is
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protecting. Usually it is not predictable or controllable as to
which TLS client will initiate a connection. See Figure 2.
The TLS proxy is provisioned with the server's certificates and
private keys so that it may either decrypt or terminate the TLS
connection on behalf of the server. In some instances, the TLS proxy
may periodically retrieve the private keys and associated
certificates from an external secure distribution service, such as a
HSM. Traffic between the TLS proxy and server may be encrypted or in
the clear; the former configuration is typical of a perimeter
firewall while the latter of a load-balancer.
____________
/
/ S
_----__ / .--.
/ \____ / |==|
__/ / |--|
/ +-+ +-+ \__ | .....|==| S
( | | | | \ | . |--| .--.
( |C| +-+ |C| +-+ ) +---+ . |::| |==|
\ | | | | | | | | ) | |... |__| |--|
( +-+ |C| +-+ |C|..............| P | S " " |==|
\ | | | | ) | |... .--. |--|
( +-+ +-+ / +---+ . |==| |::|
\_. ) | . |--| |__|
\.. / | ..|==| " "
\____--' \ |--|
\ |::| Administrative
External Network \ |__| Domain
\ " "
\____________
Figure 2: Inbound TLS proxy
3.3.1. OP-11: TLS offloading
Deployment mode: inline
Offloads crypto operations from the application server to a TLS
Proxy. This is not a typical security function on its own, but it
facilitates security control insertion downstream. As this is in the
same administrative domain, it is presumed that a TLS Proxy can be
provisioned with the appropriate keys when the TLS Server is
configured or managed.
TLS 1.3 considerations: no impact.
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3.3.2. OP-12. Content distribution and application load balancing
Deployment mode: inline
Load balancers deployed in front of services provide resiliency
against denial of service attacks. TLS proxy functionality provides
access to the cleartext application layer data to enable service-
tailored load balancing. Similar to OP-11, it is presumed that a TLS
Proxy can be provisioned with the appropriate keys when the TLS
Server is configured or managed.
This practice may be combined with OP-11.
TLS 1.3 considerations: no impact.
3.3.3. OP-13: Network-based Threat Protection (server)
Deployment mode: inline and out-of-band
Web application firewalls (WAF) and firewalls protect servers and
services against a range of threats by inspecting the data in the TLS
session with a variety of analytical techniques (e.g., signatures,
heuristics, statistical models, machine learning). This practice is
identical in function to OP-8, but focused on threat prevention of
inbound requests to servers and services.
TLS 1.3 considerations for inline deployment mode: no capability
impact. Per Section 4.1, the network security device must explicitly
terminate the TLS connection from the client.
TLS 1.3 considerations for out-of-band mode: alternative approach
required. Per Section 4.1, active participation in the TLS exchange
is required to inspect the session.
3.3.4. OP-14: Full Packet Capture
Deployment mode: inline and out-of-band
A network security device stores a copy of all decrypted traffic that
meets a given filter. This traffic may be continuously captured in a
rolling buffer for use in future forensic analysis, incident
response, or computationally intensive retrospective analysis. This
collection may also be selectively enabled to support application
troubleshooting.
TLS 1.3 considerations for inline deployment mode: no capability
impact. Per Section 4.1, the network security device must explicitly
terminate the TLS connection from the client.
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TLS 1.3 considerations for out-of-band mode: alternative approach
required. Per Section 4.1, offline decryption is not possible.
3.3.5. OP-15: Application Layer Gateway (ALG)
Deployment mode: inline
To conduct protocol conformance checks and rewrite embedded IP
addresses and TCP/UDP ports within the application layer payload for
traffic traversing a NAT boundary. While not strictly a security
function, this capability may typically be found in firewalls along
with the NAT supporting functions.
TLS 1.3 considerations: no impact.
4. Changes in TLS v1.3 Relevant to Security Operations
TLS v1.3 introduces a number of protocol design changes to improve
security and privacy. However, these enhancements impact current
network security operational practices that rely on the protocol
behavior of earlier TLS versions.
4.1. Perfect Forward Secrecy (PFS)
TLS 1.2 (and earlier versions) supports static RSA and Diffie-Hellman
(DH) cipher suites, which enables the server's private key to be
shared with a TLS proxy. TLS 1.3 has removed support for these
cipher suites in favor of supporting only ephemeral mode Diffie-
Hellman to provide perfect forward secrecy (PFS). As a result of
this enhancement, it would no longer possible for a server to share a
key with the middlebox in advance, which in turn implies that the
middlebox cannot gain access to the TLS session data.
4.2. Encrypted Server Certificate
TLS 1.2 (and earlier versions) sends the ClientHello, ServerHello and
Certificate messages in clear-text. In TLS 1.3, the Certificate
message is encrypted whereby hiding the server identity from any
intermediary. As a result of this enhancement, it would no longer be
possible to observe the server certificate without inspection the
encrypted TLS payload.
TLS proxies which implement a selective decryption policy will need
to alter their behavior to accommodate TLS 1.3. In TLS 1.2 (and
earlier), the proxy could observe the TLS handshake till seeing the
clear text server certificate to make the decryption policy decision.
For example, a proxy may not be permitted to decrypt certain types of
traffic such as those going to a banking and health care service.
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However, in TLS 1.3, the TLS proxy must participate in both
handshakes (i.e., client-to-proxy; and proxy-to-server) in order to
view the server certificate. This change will impose a slight
increase in load per connection on the proxy.
5. Security Considerations
This entire document discusses security considerations in existing
operational security practices interacting with TLS. It notes where
existing practices will have to be adjusted to remain effective due
to TLS v1.3 improvements.
These operational practices involve both good faith and malicious
client applications. The former category typically exhibits
consistently identifiable behavior and does not actively prevent any
transit inspection devices from performing application identification
for visibility and control purposes. The latter category of
applications actively attempts to circumvent network security
controls by deliberately manipulating various protocol headers,
injecting specific messages, and varying payload sizes in order to
avoid identification or to masquerade as a different permitted
application.
6. IANA Considerations
This document has no IANA actions.
7. Appendix A: Summary Impact to Operational Practices with TLS 1.3
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+---------------------------------------------+-----------------------+
| Operational Practice | Impact with TLS 1.3 |
+---------------------------------------------+-----------------------+
| OP-1: AUP enforcement (headers only) | reduced effectiveness |
| OP-2: Behavior analytics (headers only) | reduced effectiveness |
| OP-3: Crypto compliance monitoring (server) | reduced effectiveness |
| OP-4: Crypto compliance monitoring (client) | reduced effectiveness |
| OP-5: AUP enforcement (payload) | no capability impact |
| OP-6: Data loss prevention compliance | no capability impact |
| OP-7: Granular network segmentation | no capability impact |
| OP-8: Network protection (client) | no capability impact |
| OP-9: Protecting challenging end points | no capability impact |
| OP-10: Content Injection | no capability impact |
| OP-11: TLS offloading | no impact |
| OP-12: Application load balancing | no impact |
| OP-13: inline: Network protection (server) | no operational impact |
| OP-13: oob: Network protection (server) | alternative required |
| OP-14: inline: Full packet capture | no operational impact |
| OP-14: oob: Full packet capture | alternative required |
| OP-15: Application layer gateway | no impact |
+---------------------------------------------+-----------------------+
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8404] Moriarty, K., Ed. and A. Morton, Ed., "Effects of
Pervasive Encryption on Operators", RFC 8404,
DOI 10.17487/RFC8404, July 2018,
<https://www.rfc-editor.org/info/rfc8404>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
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8.2. Informative References
[ESNI] Rescorla, E., Oku, K., Sullivan, N., and C. Wood,
"Encrypted Server Name Indication for TLS 1.3", draft-
ietf-tls-esni-05 (work in progress), November 2019.
[NONCE_FAIL]
Jovanovic, P., "Nonce-disrespecting adversaries: Practical
forgery attacks on GCM in TLS", 2016,
<https://www.usenix.org/conference/woot16/workshop-
program/presentation/bock>.
[TLS_VULNERABILITY]
Shenefiel, C., "PRNG Failures and TLS Vulnerabilities in
the Wild", 2017,
<https://rwc.iacr.org/2017/Slides/david.mcgrew.pptx>.
[WEAK_K2] Heninger, N., "Weak Keys Remain Widespread in Network
Devices", 2016, <https://www.cis.upenn.edu/~nadiah/papers/
weak-keys/weak-keys.pdf>.
[WEAK_KEY]
Halderman, A., "Mining your Ps and Qs: Detection of
widespread weak keys in network devices", 2012,
<https://www.usenix.org/conference/usenixsecurity12/
technical-sessions/presentation/heninger>.
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Acknowledgments
The authors thank Andrew Ossipov, Flemming Andreasen, Kirsty Paine,
David McGrew, and Eric Vyncke for their contributions and valuable
feedback.
Authors' Addresses
Nancy Cam-Winget
Cisco Systems, Inc.
3550 Cisco Way
San Jose, CA 95134
USA
EMail: ncamwing@cisco.com
Eric Wang
Cisco Systems, Inc.
3550 Cisco Way
San Jose, CA 95134
USA
EMail: ejwang@cisco.com
Roman Danyliw
Software Engineering Institute
EMail: rdd@cert.org
Roelof DuToit
Broadcom
EMail: roelof.dutoit@broadcom.com
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