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OPSEC Working Group                                        N. Cam-Winget
Internet-Draft                                                   E. Wang
Intended status: Informational                       Cisco Systems, Inc.
Expires: January 29, 2021                                     R. Danyliw
                                          Software Engineering Institute
                                                               R. DuToit
                                                                Broadcom
                                                           July 28, 2020


      Impact of TLS 1.3 to Operational Network Security Practices
                     draft-ietf-opsec-ns-impact-02

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 29, 2021.

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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   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
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  How TLS is used to enable Network-Based Security Solutions  .   4
   4.  Changes in TLS 1.3 Relevant to Security Operations  . . . . .   5
     4.1.  Perfect Forward Secrecy (PFS) . . . . . . . . . . . . . .   5
     4.2.  Encrypted Server Certificate  . . . . . . . . . . . . . .   5
   5.  Network Security Operational Practices  . . . . . . . . . . .   6
     5.1.  Passive TLS Inspection  . . . . . . . . . . . . . . . . .   6
       5.1.1.  OP-1. Acceptable Use Policy (AUP) Enforcement (via
               header inspection). . . . . . . . . . . . . . . . . .   7
       5.1.2.  OP-2. Network Behavior Analytics  . . . . . . . . . .   7
       5.1.3.  OP-3. Crypto, Security  and Security Policy
               Compliance (server) . . . . . . . . . . . . . . . . .   8
       5.1.4.  OP-4. Crypto and Security Policy Compliance (client)    8
     5.2.  Outbound TLS Proxy  . . . . . . . . . . . . . . . . . . .   9
       5.2.1.  OP-5: Acceptable Use Policy (AUP) Enforcement (via
               payload inspection) . . . . . . . . . . . . . . . . .  10
       5.2.2.  OP-6: Data Loss Prevention Compliance . . . . . . . .  10
       5.2.3.  OP-7: Granular Network Segmentation . . . . . . . . .  10
       5.2.4.  OP-8: Network-based Threat Protection (client)  . . .  10
       5.2.5.  OP-9: Protecting Challenging End Points . . . . . . .  11
       5.2.6.  OP-10: Content Injection  . . . . . . . . . . . . . .  11
     5.3.  Inbound TLS Proxy . . . . . . . . . . . . . . . . . . . .  11
       5.3.1.  OP-11: TLS offloading . . . . . . . . . . . . . . . .  12
       5.3.2.  OP-12. Content distribution and application load
               balancing . . . . . . . . . . . . . . . . . . . . . .  13
       5.3.3.  OP-13: Network-based Threat Protection (server) . . .  13
       5.3.4.  OP-14: Full Packet Capture  . . . . . . . . . . . . .  13
       5.3.5.  OP-15: Application Layer Gateway (ALG)  . . . . . . .  14
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Appendix A: Summary Impact to Operational Practices with TLS
       1.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     9.2.  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

   o  by itself, a single system may not be able to detect and mitigate
      threats

   In response to the adoption of new technologies, protocols and
   threats, these security architectures must evolve to remain
   effective.  [RFC8404] documented a need to evolve 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 1.2 [RFC5246] (and earlier) traffic to
   implement security policy, detection or mitigation of threats; and
   the impact on these practices with improvements made in TLS 1.3
   [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



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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   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).  A TLS Proxy is unable to proxy a PSK based
   session unless it is on-path and has proxied the session leading to



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   the PSK.  TLS client authentication requires additional provisioning
   for X.509 certificate on the TLS Server side.  It does not have
   impact on the deployment scenarios though.

4.  Changes in TLS 1.3 Relevant to Security Operations

   TLS 1.3 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.  [RFC7525] initiated the recommendation of
   using AEAD cipher suites and specifically decoupling the cipher suite
   negotiation based on the RSA key transport; this followed with TLS
   1.3 explicitly removing 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 be 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.ss

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.
   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.







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5.  Network Security Operational Practices

   Specific network security operational practices applied to TLS 1.2
   (and earlier) are described in subsequent sub-sections.  They are
   categorized into the following deployment scenarios:

   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 current 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 1.3 is categorized and explained.  The categorized impacts to
   practices when migrating to TLS 1.3 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 1.3 traffic

   o  alternative approach required - this practice will not work with
      TLS 1.3 traffic

   It should be noted that [ECH] will further reduce the effectiveness
   (passive inspection) or prevent certain practices (outbound proxy)
   from being deployed.  More study is required in this area.

5.1.  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



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   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.

5.1.1.  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 considerations: 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.

5.1.2.  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-



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   arrival times, and similar outer connection behavior.  They match
   encrypted connections against known application patterns; identify
   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.

5.1.3.  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.

5.1.4.  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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5.2.  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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5.2.1.  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.

5.2.2.  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.  Note that the firewall may be implemented and enforced
   either at the endpoint or by the network infrastructure.

   TLS 1.3 considerations: no capability impact.  See Section 4.2 if a
   selective decryption policy is used.

5.2.3.  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.

5.2.4.  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



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   models, machine learning).  This practice is a superset of OP-2.
   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.

5.2.5.  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.

5.2.6.  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.

5.3.  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



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   the same administrative domain as the server(s) or service(s) it is
   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

5.3.1.  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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5.3.2.  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.

5.3.3.  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.

5.3.4.  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.

5.3.5.  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.

6.  Security Considerations

   This document presents common and existing security monitoring and
   detection functionality and how it interacts with TLS.  It further
   notes where existing practices will have to be adjusted to remain
   effective as these solutions transition to include TLS 1.3
   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.

7.  IANA Considerations

   This document has no IANA actions.

8.  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             |
 +---------------------------------------------+-----------------------+

9.  References

9.1.  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>.

   [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>.

   [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>.






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   [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>.

9.2.  Informative References

   [ECH]      Rescorla, E., Oku, K., Sullivan, N., and C. Wood, "TLS
              Encrypted Client Hello", draft-ietf-tls-esni-07 (work in
              progress), June 2020.

   [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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