Effects of Pervasive Encryption on Operators

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12           Informational
          13 14 15 16 17 18 19 20 21 22 23 24 25                        
Network Working Group                                        K. Moriarty
Internet-Draft                                                  Dell EMC
Intended status: Informational                                 A. Morton
Expires: August 17, 2017                                       AT&T Labs
                                                       February 13, 2017

                     Effect of Pervasive Encryption


   Increased use of encryption impacts operations for security and
   network management causing a shift in how these functions are
   performed.  In some cases, new methods to both monitor and protect
   data will evolve.  In other cases, the ability to monitor and
   troubleshoot could be eliminated.  This draft includes a collection
   of current security and network management functions that may be
   impacted by the shift to increased use of encryption.  This draft
   does not attempt to solve these problems, but rather document the
   current state to assist in the development of alternate options to
   achieve the intended purpose of the documented practices.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Network Service Provider Monitoring . . . . . . . . . . . . .   5
     2.1.  Middlebox Monitoring  . . . . . . . . . . . . . . . . . .   5
       2.1.1.  Load Balancers  . . . . . . . . . . . . . . . . . . .   5
       2.1.2.  Traffic Analysis Fingerprinting . . . . . . . . . . .   6
       2.1.3.  Traffic Surveys . . . . . . . . . . . . . . . . . . .   6
       2.1.4.  Deep Packet Inspection (DPI)  . . . . . . . . . . . .   7
       2.1.5.  Connection to Proxy for Compression . . . . . . . . .   7
       2.1.6.  Mobility Middlebox Content Filtering  . . . . . . . .   8
       2.1.7.  Access and Policy Enforcement . . . . . . . . . . . .   8
     2.2.  Network Monitoring for Performance Management and
           Troubleshooting . . . . . . . . . . . . . . . . . . . . .   9
   3.  Encryption in Hosting SP Environments . . . . . . . . . . . .  10
     3.1.  Management Access Security  . . . . . . . . . . . . . . .  10
       3.1.1.  Customer Access Monitoring  . . . . . . . . . . . . .  11
       3.1.2.  Application SP Content Monitoring . . . . . . . . . .  11
     3.2.  Hosted Applications . . . . . . . . . . . . . . . . . . .  13
       3.2.1.  Monitoring needs for Managed Applications . . . . . .  13
       3.2.2.  Mail Service Providers  . . . . . . . . . . . . . . .  14
     3.3.  Data Storage  . . . . . . . . . . . . . . . . . . . . . .  14
       3.3.1.  Host-level Encryption . . . . . . . . . . . . . . . .  15
       3.3.2.  Disk Encryption, Data at Rest . . . . . . . . . . . .  15
       3.3.3.  Cross Data Center Replication Services  . . . . . . .  16
   4.  Encryption for Enterprises  . . . . . . . . . . . . . . . . .  16
     4.1.  Monitoring Needs of the Enterprise  . . . . . . . . . . .  17
       4.1.1.  Security Monitoring in the Enterprise . . . . . . . .  17
       4.1.2.  Application Performance Monitoring in the Enterprise   18
       4.1.3.  Enterprise Network Diagnostics and Troubleshooting  .  19
     4.2.  Techniques for Monitoring Internet Session Traffic  . . .  20
   5.  Security Monitoring for Specific Attack Types . . . . . . . .  22
     5.1.  Mail Abuse and SPAM . . . . . . . . . . . . . . . . . . .  22
     5.2.  Denial of Service . . . . . . . . . . . . . . . . . . . .  22
     5.3.  Phishing  . . . . . . . . . . . . . . . . . . . . . . . .  23
     5.4.  Botnets . . . . . . . . . . . . . . . . . . . . . . . . .  23
     5.5.  Malware . . . . . . . . . . . . . . . . . . . . . . . . .  24
     5.6.  Spoofed Source IP Address Protection  . . . . . . . . . .  24
     5.7.  Further work  . . . . . . . . . . . . . . . . . . . . . .  24
   6.  Application-based Flow Information Visible to a Network . . .  24
     6.1.  TLS Server Name Indication  . . . . . . . . . . . . . . .  25

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     6.2.  Application Layer Protocol Negotiation (ALPN) . . . . . .  25
     6.3.  Content Length, BitRate and Pacing  . . . . . . . . . . .  25
   7.  Response to Increased Encryption and Looking Forward  . . . .  26
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  27
   11. Appendix: Impact on Mobility Network Optimizations and New
       Services  . . . . . . . . . . . . . . . . . . . . . . . . . .  27
     11.1.  Effect of Encypted ACKs  . . . . . . . . . . . . . . . .  27
     11.2.  Effect of Encrypted Transport Headers  . . . . . . . . .  28
     11.3.  Effect of Encryption on New Services . . . . . . . . . .  29
     11.4.  Effect of Encryption on Mobile Network Evolution . . . .  30
   12. Informative References  . . . . . . . . . . . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  35

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.  Session
   encryption helps to prevent both passive and active attacks on
   transport protocols; more on pervasive monitoring can be found in the
   Confidentiality in the Face of Pervasive Surveillance: A Threat Model
   and Problem Statement [RFC7624].  The Internet Architecture Board
   (IAB) released a statement advocating for increased use of encryption
   in November 2014.  Views on acceptable encryption have also shifted
   and are documented in "Opportunistic Security" (OS) [RFC7435], where
   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 upgrade to authenticated encryption.  These
   efforts are necessary to improve end user's expectation of privacy,
   making pervasive monitoring cost prohibitive.  Active attacks are
   still possible on sessions where unauthenticated sessions are in use.
   The push for ubiquitous encryption via OS is specific to improving
   privacy for everyday users of the Internet.

   Although there is a push for OS, there is also work being done to
   improve implementation development and configuration flaws of TLS and
   DTLS sessions to prevent active attacks used to monitor or intercept
   session data.  The (UTA) working group is in process of publishing
   documentation to improve the security of TLS and DTLS sessions.  They
   have documented the known attack vectors in [RFC7457] and have
   documented Best Practices for TLS and DTLS in [RFC7525] and have
   other documents in the queue.

   Estimates for session encryption from spring 2015 approximate that
   about 30% of web sites have session encryption enabled, according to

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   the Electronic Frontier Foundation [EFF].  The Mozilla Foundation
   maintains statistics on SSL/TLS usage and as of March 2015, 64% of
   HTTP transactions are encrypted.  Enterprise networks such as EMC
   observe that about 78% of outbound employee traffic was encrypted in
   June 2014.  Although the actual number of sites may only be around
   30%, they include some of the most visited sites on the Internet for
   corporate users.

   In addition to encrypted web site access (HTTP over TLS), there are
   other well-deployed application level transport encryption efforts
   such as mail transfer agent (MTA)-to-MTA session encryption transport
   for email (SMTP over TLS) and gateway-to-gateway for instant
   messaging (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 PGP for email and encryption (e.g.  Off-the-Record
   (OTR)) for Extensible Messaging and Presence Protocol (XMPP) are used
   by those interested to protect their data as it crosses intermediary
   servers, preventing the vulnerability described 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)
   will impact operations for security and network management, causing a
   shift in how these functions are performed.  In some cases new
   methods to monitor and protect data will evolve, for other cases the
   need may be eliminated.  This draft includes a collection of current
   security and network management functions that may be impacted by
   this shift to increased use of encryption.  This draft does not
   attempt to solve these problems, but rather document the current
   state to assist in the development of alternate options to achieve
   the intended purpose of the documented practices.

   In this document we consider several different forms of service
   providers, so we distinguish between them with adjectives.  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 end-point in
   communications with the application user, and hosting service
   providers lease computing, storage, and communications systems in
   datacenters.  In practice, many companies perform two or more service
   provider roles, but may be historically associated with one.

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2.  Network Service Provider Monitoring

   Network Service Providers (SP) are responding to encryption on the
   Internet, some helping to increase the use of encryption and others
   preventing its use.  Network SPs for this definition include the
   backbone Internet Service providers as well as those providing
   infrastructure at scale for core Internet use (hosted infrastructure
   and services such as email).

   Following the Snowden revelations, application service providers
   responded by encrypting traffic between their data centers to prevent
   passive monitoring from taking place unbeknownst to the providers
   (Yahoo, Google, etc.).  Large mail service providers also began to
   encrypt session transport to hosted mail services.  This had an
   immediate impact to help protect the privacy of users data, but
   created a problem for network operators.  They could no longer gain
   access to session streams resulting in actions by several to regain
   their operational practices that previously depended on cleartext
   data sessions.

   The EFF reported [EFF2014] several network service providers taking
   steps to prevent the use of SMTP over TLS by breaking STARTTLS
   (section 3.2 of [RFC7525]), preventing the negotiation process
   resulting in fallback to the use of clear text.  The use of
   encryption prevents middle boxes from performing functions that range
   from some methods of load balancing to monitoring for attacks or
   enabling "lawful intercept", such that described in [ETSI101331] and
   [CALEA] in the US.  These practices are representative of the
   struggles administrators have with changes in their ability to
   monitor and manage traffic.

2.1.  Middlebox Monitoring

   Network service providers use various monitoring techniques for
   security and operational purposes.  The following subsections detail
   the purpose of each type of monitoring and what protocol fields are
   used to accomplish the task.

2.1.1.  Load Balancers

   Some network architectures need to share significant traffic load
   among a pool of parallel systems, to achieve the needed capacity.
   Load Balancer devices (a form of middlebox) provide the traffic-
   sharing function, according to pre-defined rules.  A general rule for
   many load balancers requires that all packets comprising an
   individual flow should to be routed to the same system in the load
   balancer's pool.  The definition of a flow will be based on a
   combination of header fields, often as many as five for 5-tuple flows

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   (including addresses and ports for source and destination, and one
   additional field such as the DSCP or other priority marking).
   Encryption that conceals or replaces the original IP header and/or
   transport header with modified addresses or ports may result in a set
   of flows being treated as one for load balancing purposes, which
   could cause uneven traffic load levels in the pool and unnecessary
   congestion when capacity limits are approached.

2.1.2.  Traffic Analysis Fingerprinting

   Fingerprinting is used in traffic analysis and monitoring to identify
   traffic streams that match certain patterns.  This technique may be
   used with clear text or encrypted sessions.  Some Distributed Denial
   of Service (DDoS) prevention techniques at the Network SP 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.

   The first/obvious trigger for DDoS mitigation is uncharacteristic
   traffic volume and/or congestion at various points associated with
   the attackee's communications.  One approach to mitigate such an
   attack involves distinguishing attacker traffic from legitimate user
   traffic through analysis.  The ability to examine layers and payloads
   above transport provides a new range of filtering opportunities at
   each layer in the clear.  Fewer layers are in the clear means reduced
   filtering opportunities to mitigate attacks.

   Traffic analysis fingerprinting could also be used on web traffic to
   perform passive monitoring and invade privacy.

   For example, browser fingerprints are comprised of many
   characteristics, including User Agent, HTTP Accept headers, browser
   plug-in details, screen size and color details, system fonts and time
   zone.  [PANO] will audit these details for users.  A monitoring
   system could easily identify a specific browser, and by correlating
   other information, identify a specific user.

2.1.3.  Traffic Surveys

   Internet traffic surveys are useful in many well-intentioned
   pursuits, such as CAIDA data [CAIDA] and SP network design 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 required a view of traffic
   composition and reports with acceptable accuracy.  As application
   designers and network operators both continue to seek optimizations,
   the role of traffic surveys from passive monitoring grows in

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   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 e-mail access).  It remains to be seen whether more
   complex inferences can be mastered to produce the same monitoring

2.1.4.  Deep Packet Inspection (DPI)

   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, and authorized parties 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

   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
   20ms delay when receiving a simple Web page or email, or an instant
   message response, but will very likely notice a re-buffering 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 the traffic type has been required
   to be known to date.  Application and transport layer encryption make
   the traffic type detection less accurate, and affect queue

2.1.5.  Connection to Proxy for Compression

   In contrast to DPI, various applications exist to provide data
   compression in order to conserve the life of the user's mobile data
   plan and optimize delivery over the mobile link.  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

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   application to connect to a centralized server as a proxy, 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.  As the percentage of connections using encryption increases,
   these data compression services will be rendered less effective, or
   worse, they will adopt undesirable security practices in order to
   gain access to the unencrypted data flows.

2.1.6.  Mobility Middlebox Content Filtering

   Service Providers may, from time to time, be requested by law
   enforcement agencies to block access to particular sites such as
   online betting and gambling, or access to dating sites.  Content
   Filtering can also happen at the endpoints or at the edge of
   enterprise networks.  This section is intended to merely document
   this current practice by operators and the effects of encryption on
   the practice.

   Content filtering in the mobile network usually occurs in the core
   network.  A proxy is installed which analyses the transport metadata
   of the content users are viewing and either filters content based on
   a blacklist of sites or based on the user's pre-defined profile (e.g.
   for age sensitive content).  Although filtering can be done by many
   methods one common method occurs when a DNS lookup of a hostname in a
   URL which appears on a government or recognized block-list( [RFC7858]
   aims to address this).  The subsequent requests to that domain will
   be re-routed to a proxy which checks whether the full URL matches a
   blocked URL on the list, and will return a 404 if a match is found.
   All other requests should complete.

   See the Appendix for more information on "Encryption Impact on
   Mobility Network Optimizations and New Services".  Parental Controls

   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, which will not work on encrypted content.

2.1.7.  Access and Policy Enforcement

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   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.  Network Access

   Approved access to a network is a prerequisite to requests for
   Internet traffic - hence network access, including any authentication
   and authorization, is not impacted by encryption.

   Cellular networks often 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.  This
   feature may be impacted if encryption hides the details of the
   content domain from the network.  This topic and related material are
   described further in the Appendix.  Regulation and policy enforcement

   Mobile networks (and usually 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.

   These functions are impacted by encryption, typically by allowing a
   less granular means of implementation.  The enforcement of any Net
   Neutrality regulations is unlikely to be affected by content being
   encrypted.  The IETF's Policy on Wiretapping can be found in
   [RFC2804], which does not support wiretapping in standards.

2.2.  Network Monitoring for Performance Management and Troubleshooting

   Similar to DPI, 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 such monitoring activities without clear text
   access to the application layers of interest, but 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 availability is a key metric for Service Level
   Agreements and subscription rebates.  Also, there may be more cases

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   of user communication failures when the additional encryption
   processes are introduced, leading to more customer service contacts
   and (at the same time) less information available to network
   operations repair teams.

   With the growing use of WebSockets [RFC6455], 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 systems sees only "HTTP port 443", it
   cannot distinguish application streams that would benefit from
   priority queueing from others that would not.

3.  Encryption in Hosting 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 only increased that
   pressure to provide more secure access and session encryption to
   protect the management of hosted environments as well as for 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 SP (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

   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-

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3.1.1.  Customer Access Monitoring

   Hosted applications that allow some level of customer management
   access may also require monitoring by the hosting service provider.
   The monitoring needs 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
   either through session monitoring or log evaluation to ensure
   security service level agreements (SLA) 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 an:

   2-tuple  IP-level with source and destination IP addresses alone, or

   5-tuple  IP and protocol-level with source IP address, destination IP
      address, protocol number, source port number, and destination port

   Session encryption at the application level, TLS for example,
   currently allows access to the 5-tuple.  IP-level encryption, such as
   IPsec in tunnel mode prevents access to the 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 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.  Application SP Content Monitoring

   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 which access the contents of IP packets (passive
   methods of measurement, as defined in [RFC7799]).  These processes
   are typically for service assurance or security purposes and form an
   integral and mission-critical part of data center operations.

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   Examples include:

      - Network Performance Monitoring/Application Performance

      - Intrusion defense/prevention systems

      - Malware detection

      - Fraud Monitoring

      - Application DDOS protection

      - Cyber-attack investigation

      - Proof of regulatory compliance

   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 listed above.

   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 can be used to allow
   trusted service assurance and security processes to access
   unencrypted data.  These include SSL/TLS decryption in dedicated
   units, which then forward packets to trusted tools, or by real-time
   or post-capture decryption in the tools themselves.

   Data center operators may also maintain packet recordings in order to
   be able to investigate attacks, breach of internal processes, etc.
   In some industries, organizations may be legally required to maintain
   such information for compliance purposes.  Investigations of this
   nature require access to the unencrypted contents of the packet.

   Application Service Providers may offer content-level monitoring
   options to detect intellectual property leakage, or other attacks.
   The use of session encryption will prevent Data Leakage Protection
   (DLP) used on the session streams from accessing content to search on
   keywords or phases to detect such leakage.  DLP is often used to
   prevent the leakage of Personally Identifiable Information (PII) as
   well as financial account information, Personal Health Information
   (PHI), and Payment Card Information (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

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   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 users system in
   an organization as alternate or additional monitoring points of
   content, however this is not frequently done in a service provider

   Secure overlay networks (for example, VXLAN) may be used in multi-
   tenancy scenarios to provide isolation assurance and thwart some
   active attacks.  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.  Tunneled traffic on VXLAN can be secured by
   using IPsec, but this adds the requirement for authentication
   infrastructure and may reduce packet transfer performance.
   Deployment of data path acceleration technologies can help to
   mitigate the performance issues, but they also bring more complex
   networking and management.

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 service level agreement expectations for
   availability and performance as well as for security functions
   including malware detection.

3.2.1.  Monitoring needs for Managed Applications

   Performance, availability, and other aspects of a SLA are often
   collected through passive monitoring.  For example:

   o  Availability: ability to establish connections with hosts to
      access applications, and discern the difference between network or
      host-related causes of unavailability.

   o  Performance: ability to complete transactions within a target
      response time, and discern the difference between network or host-
      related causes of excess response time.

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   Here, as with all passive monitoring, the accuracy of inferences are
   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.

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], malware [Section 5.6],
   and phishing attacks [Section 5.3] before mail is directed to the
   organization's equipment.  In both of these cases, content of the
   messages and headers is monitored to detect SPAM, malware, phishing,
   and other messages that may be considered an attack.

   STARTTLS ought 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.

   Many efforts are emerging to improve user-to-user encryption to
   protect end user's privacy.  There are no clear front runners with
   efforts ranging from proprietary to open source ones like "Dark

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 both
   approaches from what may be done today.

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3.3.1.  Host-level Encryption

   For higher security and/or privacy of data and applications, options
   that provide end-to-end encryption of the data from the users desktop
   or server to the storage platform may be preferred.  With this
   description, host level encryption includes any solution that
   encrypts data at the object level, not 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.  Host-level encryption is useful when data storage is
   hosted, or scenarios when storage location is determined based on
   capacity or based on a set of parameters to automate decisions.  This
   could mean that large data sets 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 could be
   based on the transaction type.  Host-level encryption is grouped
   separately for the purpose of this document as the monitoring needs
   as this data can be stored in multiple locations including off-site
   remote storage platforms.  If session encryption is used, the
   protocol is likely to be TLS.  Monitoring for Hosted Storage

   The general monitoring needs of hosted storage solutions that use
   host-level (object) encryption is described in this subsection.
   Solutions might include backup services and external storage
   services, such as those that burst data that exceeds internal limits
   on occasion to external storage platforms operated by a third party.

   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

   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 (SED).  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.

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   The general monitoring needs for transport of data to storage
   platforms, where object level encryption is performed close to or on
   the storage platform are similar to those described in the section on
   Monitoring for Hosted Storage.  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.

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 iSCSI [RFC7143] or FC/IP [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.  Monitoring Of IPSec for Data Replication Services

   The general monitoring needs for data replication are described in
   this subsection.

   Monitoring of data flows between data centers may be performed for
   security and operational purposes and would typically concentrate
   more on the operational needs since these flows are essentially
   virtual private networks (VPN) 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 the "Monitoring for Hosted Storage

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

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   operational purposes may be necessary to reduce the need to break
   encryption and thus privacy of users (other policies may apply in
   some enterprise settings).

4.1.  Monitoring Needs 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.  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 or more likely these days through
       malware and trojans),

   2.  detect viruses/malware entering the network via email or web

   3.  detect malware/Trojans in action, possibly connecting to remote

   4.  detect attacks (Cross site scripting and other common web related

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   5.  track misuse and abuse by employees,

   6.  restrict the types of protocols permitted to/from the entire
       corporate environment,

   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 encrypted protocols.  This includes lateral movement, Command
   and Control, and Data Exfiltration.  Detecting these functions are
   important to effective monitoring and mitigation of malicious
   traffic, not limited to malware.

4.1.2.  Application Performance Monitoring 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 needs.

   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 need.  Content Delivery
   Networks (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) will provide this
   [I-D.ietf-ippm-6man-pdm-option].  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 7 of
   [I-D.ietf-ippm-6man-pdm-option].  For these and other reasons,
   [I-D.ietf-ippm-6man-pdm-option] requires that the PDM DOH option be

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   explicitly turned on by administrative action in each host where this
   measurement feature will be used.

4.1.3.  Enterprise Network Diagnostics and Troubleshooting

   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 the modern 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.  NAT

   Content Delivery Networks (CDNs) and NATs obscure the ultimate
   endpoint designation.  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, 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.  TCP Pipelining/Session Multiplexing

   TCP Pipelining/Session Multiplexing used mainly by middle boxes today
   allow for multiple end user sessions to share the same TCP
   connection.  Today's network troubleshooter often relies upon session
   decryption to tell which packet belongs to which end user as the logs
   are currently inadequate for the analysis needed.

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   With the advent of HTTP2, session multiplexing will be used
   ubiquitously, both on the Internet and in the private data center.  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.  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, but techniques like that of data leakage
   prevention tools at a proxy would not be possible if encrypted
   traffic can not be intercepted, encouraging alternate options such as
   performing these functions at the edge.

   Data leakage detection prevention (DLP) tools intercept traffic at
   the Internet gateway or proxy services with the ability to man-in-
   the-middle (MiTM) encrypted session traffic (HTTP/TLS).  These tools
   may use key words important to the enterprise including business
   sensitive information such as trade secrets, financial data,
   personally identifiable information (PII), or personal health
   information (PHI).  Various techniques are used to intercept HTTP/TLS
   sessions for DLP and other purposes, and are described in
   "Summarizing Known Attacks on TLS and DTLS" [RFC7457].  Note: many
   corporate policies allow access to personal financial and other sites
   for users without interception.

   Monitoring traffic patterns for anomalous behavior such as increased
   flows of traffic that could be bursty at odd times or flows to

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   unusual destinations (small or large amounts of traffic).  This
   traffic may or may not be encrypted and various methods of encryption
   or just obfuscation may be used.

   Restrictions on traffic to approved sites: Web proxies are sometimes
   used to filter traffic, allowing only access to well-known sites
   found to be legitimate and free of malware on last check by a proxy
   service company.  This type of restriction is usually not noticeable
   in a corporate setting, but may be to those in research who are
   unable to access colleague's individual sites or new web sites 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 proxy log alerts and review.  Home mail account access
   may be blocked in corporate settings to prevent another vector for
   malware to enter as well as for intellectual property to leak 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.  Web proxy solutions monitor and potentially
   restrict access based on the destination URL or the 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

   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 of
   monitoring intellectual property leakage 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 devices that do not fit the desktop
   category, but 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 e-mail 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 and optimization based on
   monitoring (DPI) would suffer the same fate.

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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.

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 combated 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], and [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 effect 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 abuse mitigation efforts.

5.2.  Denial of Service

   Response to Denial of Service (DoS) attacks are typically coordinated
   by the SP 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
   DDoS Open Threat Signaling (DOTS) working group documents in

   Data types used in DDoS attacks have been detailed in the IODEF
   Guidance draft [I-D.ietf-mile-iodef-guidance], Appendix A.2, with the

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   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 drafts.

5.3.  Phishing

   Investigations and response 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 contains an embedded attack that may be
   in an infected file or may be a link that results in the download of
   malware to the users system.

   Administrators often find it helpful to use header information to
   track down similar message in their mail queue or users inboxes to
   prevent further infection.  Combinations of To:, From:, Subject:,
   Received: from header information might be used for this purpose.
   Administrators may also search for document attachments of the same
   name, size, or containing 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 scales efforts like that of the Anti-Phishing
   Working Group (APWG).

   A full list of the fields used in phishing attack incident response
   can be found in RFC5901.  Future plans to increase privacy
   protections may limit some of these capabilities if some email header
   fields are encrypted, such as 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.  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 draft [I-D.ietf-mile-iodef-guidance],
   Appendix A.3.

5.4.  Botnets

   Botnet detection and mitigation is complex and may involve hundreds
   or thousands of hosts with numerous Command and Control (C&C)
   servers.  The techniques and data used to monitor and detect each may
   vary.  Connections to C&C servers are typically encrypted, therefore

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   a move to an increasingly encrypted Internet may not affect the
   detection and sharing methods used.

5.5.  Malware

   Malware monitoring and detection techniques vary.  As mentioned in
   the enterprise section, 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 draft [I-D.ietf-mile-iodef-guidance],
   Appendix A.1.

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 [RFC2827] and the
   unicast Reverse Path Forwarding (uRPF) mechanism [RFC2504].  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.  The Source Address Validation Improvements
   (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., SLAAC [RFC4682], SEND
   [RFC3791], DHCPv4/v6 [RFC2131][RFC3315]) and, according to this
   monitoring, set-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 may apply to various network types.

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6.1.  TLS Server Name Indication

   When initiating the TLS handshake, the Client may provide an
   extension field (server_name) which 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.  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 implementations MUST support the Server Name
   Indication (SNI) extension.

   This information is only visible if the client is populating the
   Server Name Indication extension.  This need not be done, but may be
   done as per TLS standard.  Therefore, even if existing network
   filters look out for seeing a Server Name Indication extension, they
   may not find one.  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 Server Name Indication will only indicate
   the server domain rather than a URL path.

6.2.  Application Layer Protocol Negotiation (ALPN)

   ALPN is a TLS extension which 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 which may make up streams within an
   HTTP/2 multiplex.

6.3.  Content Length, BitRate and Pacing

   The content length of encrypted traffic is effectively the same as
   the cleartext.  Although block ciphers utilise 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) may however incorporate
   several application streams over one connection, which makes the
   bitrate/pacing no longer application-specific.

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7.  Response to Increased Encryption and Looking Forward

   In the best case scenario, engineers and other innovators would work
   to solve the problems at hand in new ways rather than prevent the use
   of encryption.  It will take time to devise alternate approaches to
   achieve similar goals.

   There has already been documented cases of service providers
   preventing STARTTLS [NoEncrypt] to prevent session encryption
   negotiation on some session to inject a super cookie.  There are
   other service providers who have been injecting Java Script into
   sessions [Net-Neutral], which has obvious security implications as
   well as threatens Net-Neutrality.  The use of session encryption will
   help to prevent possible discrimination to maintain net neutrality,
   but a backlash should be expected.

   National surveillance programs have a clear need for monitoring
   terrorism [JNSLP] as do Internet security practitioners monitoring
   for criminal activities.  Governments vary on their balance between
   their need for monitoring versus the protection of user privacy,
   data, and assets.  Those that favor unencrypted access to data ignore
   the real need to protect users identity, financial transactions and
   intellectual property, which requires security and encryption to
   prevent crime.  A clear understanding of technology, encryption, and
   monitoring needs will aid in the development of solutions to
   appropriately balance the need of privacy.  As this understanding
   increases, hopefully the discussions will improve and this draft is
   meant to help further the discussion.

   Terrorists and criminals have been using encryption for many years.
   The current push to increase encryption is aimed at increasing users
   privacy.  There is already protection in place for purchases,
   financial transactions, systems management infrastructure, and
   intellectual property although this too can be improved.  The
   Opportunistic Security (OS) [RFC7435] efforts aim to increase the
   costs of monitoring through the use of encryption that can be subject
   to active attacks, but make passive monitoring broadly cost
   prohibitive.  This is meant to restrict monitoring to sessions where
   there is reason to have suspicion.

   Open questions: As the use of encryption increases, does passive
   monitoring become limited to metadata analysis?  What metadata should
   be left in protocols as they evolve to also protect users privacy?
   Can we make changes to protocols and message exchanges to alter the
   current monitoring needs at least for operations and security

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   Options are on the technology horizon that could help to end the
   struggle between the need to monitor by operators, security teams,
   and nations and those seeking to protect users privacy if they come
   to fruition.  The solutions are very interesting, but are at least
   several years out and include homomorphic encrypt, functional
   encryption, and filterable decryption [homomorphic].  This technology
   will allow for searching and pattern matching on encrypted data, but
   is still several years out.

8.  Security Considerations

   There are no additional security considerations as this is a summary
   and does not include a new protocol or functionality.

9.  IANA Considerations

   This memo makes no requests of IANA.

10.  Acknowledgements

   Thanks to our reviewers, Natasha Rooney, Kevin Smith, Ashutosh Dutta,
   Brandon Williams, Jean-Michel Combes, Nalini Elkins, Paul Barrett,
   and Stephen Farrell for their editorial and content suggestions.
   Surya K.  Kovvali provided material for the Appendix.

11.  Appendix: Impact on Mobility Network Optimizations and New Services

   This Appendix considers the effects of transport level encryption on
   existing forms of mobile network optimization techniques, as well as
   potential new services.  The material in this Appendix assumes
   familiarity with mobile network concepts, specifications, and
   architectures.  Readers who need additional background should start
   with the 3GPP's web pages on various topics of interest[Web3GPP],
   especially the article on LTE. 3GPP provides a mapping between their
   expanding technologies and the different series of technical
   specifications [Map3GPP]. 3GPP also has a canonical specification of
   their vocabulary, definitions, and acronyms [Vocab], as does the RFC
   Editor for abbreviations [RFCEdit].

11.1.  Effect of Encypted ACKs

   The stream of TCP ACKs that flow from a receiver of a byte stream
   using TCP for reliability, flow-control, and NAT/firewall transversal
   is called an ACK stream.  The ACKs contain segment numbers that
   confirm successful transmission and their RTT, or indicate packet
   loss (duplicate ACKs).  If this view of progress of stream transfer
   is lost, then the mobile network has greatly reduced ability to
   monitor transport layer performance.  When the ACK stream is

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   encrypted, it prevents the following mobile network features from

   a.  Measurement of Network Segment (Sector, eNodeB (eNB) etc.)
       characterization KPIs (Retransmissions, packet drops, Sector
       Utilization Level etc.), estimation of User/Service KQIs at
       network edges for circuit emulation (CEM), and mitigation
       methods.  The active services per user and per sector are not
       visible to a server that only services Internet Access Point
       Names (APN), and thus could not perform mitigation functions
       based on network segment view.

   b.  Retransmissions by trusted proxies at network edges that improve
       live transmission over long delay, capacity-varying networks.

   c.  Content replication near the network edge (for example live
       video, DRM protected content) to maximize QOE.  Replicating every
       stream through the transit network increases backhaul cost for
       live TV.

   d.  Ability to deploy trusted proxies that reduce control round-trip
       time (RTT) between the TCP transmitter and receiver.  The RTT
       determines how quickly a user's attempt to cancel a video is
       recognized (how quickly the traffic is stopped, thus keeping un-
       wanted video packets from entering the radio scheduler queue).

   e.  Trusted proxy with low RTT determines the responsiveness of TCP
       flow control, and enables faster adaptation in a delay & capacity
       varying network due to user mobility.  Low RTT permits use of a
       smaller send window, which makes the flow control loop more
       responsive to changing mobile network conditions.

   f.  Opportunistic RAN-Aware pacing, acceleration, and deferral of
       high volume content such as video or software updates.

11.2.  Effect of Encrypted Transport Headers

   When the Transport Header is encrypted, it prevents the following
   mobile network features from operating:

   a.  Application-type-aware network edge (middlebox) that could
       control pacing, limit simultaneous HD videos, prioritize active
       videos against new videos, etc.

   b.  For the Access Network Discovery and Selection Function (3GPP-
       ANDSF), it Impedes content-aware network selection for steering
       users or specific flows to appropriate Networks.

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   c.  For Self Organizing Networks (3GPP SON) - intelligent SON
       workflows such as content-ware MLB (Mobility Load Balancing)

   d.  For User Plane Congestion Management (3GPP UPCON) - ability to
       understand content and manage network during congestion.
       Mitigating techniques such as deferred download, off-peak
       acceleration, and outbound roamers.

   e.  Reduces the benefits IP/DSCP-based transit network delivery
       optimizations; since the multiple applications are multiplexed
       within the same 5-tuple transport connection, the DSCP markings
       would not correspond to an application flow.

   f.  Advance notification for dense data usages - If the application
       types are visible, transit network element could warn (ahead of
       usage) that the requested service consumes user plan limits, and
       transmission could be terminated.  Without such visibility the
       network might have to continue the operation and stop the
       operation after the limit, because partially loaded content
       wastes resources and may not be usable by the client thus
       increasing customer complaints.  Content publisher will not know
       user-service plans, and Network Edge would not know data transfer
       lengths before large object is requested.

11.3.  Effect of Encryption on New Services

   This section describes some new mobile services and how they might be
   affected with transport encryption:

   1.  Flow-based charging allowing zero-rated and monetized traffic;
       for example operators may charge nothing, or charge based on

   2.  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.

   3.  Rich Communication Services (3GPP-RCS) using different Quality
       Class Indicators (QCIs in LTE) - Operators offer different QoS
       classes for value-added services.  The QCI type is visible in RAN
       control plane and invisible in user plane, thus the QCI cannot be
       set properly when the application -type is unknown.

   4.  Enhanced Multimedia Broadcast/Multicast Services (3GPP eMBMS) -
       trusted edge proxies facilitate delivering same stream to

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       different users, using either unicast or multicast depending on
       channel conditions to the user.

   5.  Transport level protection is unnecessary for already protected
       content (such as content with Digital Rights Management, DRM).
       It prevents multi-user replication, and tandem encryption stages
       increase required processing cycles.

11.4.  Effect of Encryption on Mobile Network Evolution

   The transport header encryption prevents trusted transit proxies.  It
   may be that the benefits of such proxies could be achieved by end to
   end client & server optimizations and distribution using CDNs, plus
   the ability to continue connections across different access
   technologies (across dynamic user IP addresses).  The following
   aspects need to 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, and scheduling balances fairness, capacity and service
       QoE.  If most users are at the cell edge, the controller cannot
       use more complex QAM, thus reducing total cell capacity;
       similarly if a UMTS edge is serving some number of CS-Voice
       Calls, the remaining capacity for packet services is reduced.

   2.  Inbound Roamers: Mobile wireless networks service in-bound
       roamers (Users of Operator A in a foreign operator Network B) by
       backhauling their traffic though Operator B's network to Operator
       A's Network and then serving through the P-Gateway (PGW), General
       GPRS Support Node (GGSN), Content Distribution Network (CDN)
       etc., of Operator A (User's Home Operator).  Increasing window
       sizes to compensate for the path RTT will have the limitations
       outlined earlier for TCP.

   3.  Outbound Roamers: Similar to inbound roamers, users accessing
       different Core/Content network, for example domains not serviced
       via local CDNs are carried through operator network via different
       APN or GW to remote networks which increases path RTT & control

   4.  Issues in deploying CDNs in RAN: Decreasing Client-Server control
       loop requires deploying CDNs/Cloud functions that terminate
       encryption closer to the edge.  In Cellular RAN, the user IP
       traffic is encapsulated into GPSR 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

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       APN, OnDeckAPN etc.).  The scope of operator private IP addresses
       may be limited to specific APN.  Since CDNs generally operate on
       user IP flows, deploying them would require enhancing them with
       tunnel translation, etc., tunnel management functions.

   5.  While CDNs that de-encrypt flows or split-connection proxy
       (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; thus content from Small-Medium Businesses (SMBs) would not
       get such CDN benefits.

   6.  Mobile Edge Computing (MEC) initiative to push latency sensitive
       functions to the edge of the network; for example a trusted proxy
       could facilitate services between two devices in RAN without
       requiring content flow through the WebServer.

12.  Informative References

   [CAIDA]    "CAIDA [http://www.caida.org/data/overview/]".

   [CALEA]    Pub. L. No. 103-414, 108 Stat. 4279, codified at 47 USC
              1001-1010, "Communications Assistance for Law Enforcement
              Act (CALEA)".

   [EFF]      "Electronic Frontier Foundation https://www.eff.org/".

   [EFF2014]  "EFF Report on STARTTLS Downgrade Attacks

              ETSI TS 101 331 V1.1.1 (2001-08), "Telecommunications
              security; Lawful Interception (LI); Requirements of Law
              Enforcement Agencies", August 2001.

              Volume 20, 2013, Pages 502-509, Complex Adaptive Systems,
              "Homomorphic Encryption

              Elkins, N., Hamilton, R., and m. mackermann@bcbsm.com,
              "IPv6 Performance and Diagnostic Metrics (PDM) Destination
              Option", draft-ietf-ippm-6man-pdm-option-07 (work in
              progress), February 2017.

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              Kampanakis, P. and M. Suzuki, "IODEF Usage Guidance",
              draft-ietf-mile-iodef-guidance-07 (work in progress),
              November 2016.

   [JNSLP]    Surveillance, Vol. 8 No. 3, "10 Standards for Oversight
              and Transparency of National Intelligence Services

   [M3AAWG]   "Messaging, Malware, Mobile Anti-Abuse Working Group
              (M3AAWG) https://www.maawg.org/".

   [Map3GPP]  http://www.3gpp.org/technologies, "Mapping between
              technologies and specifications".

              "Comcast Wifi serving self-promotional ads via JavaScript
              injection http://arstechnica.com/tech-policy/2014/09/why-

              "ISPs Removing their Customers EMail Encryption

   [PANO]     "Panopticlick [https://panopticlick.eff.org/]".

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,

   [RFC2504]  Guttman, E., Leong, L., and G. Malkin, "Users' Security
              Handbook", FYI 34, RFC 2504, DOI 10.17487/RFC2504,
              February 1999, <http://www.rfc-editor.org/info/rfc2504>.

   [RFC2804]  IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
              DOI 10.17487/RFC2804, May 2000,

   [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, <http://www.rfc-editor.org/info/rfc2827>.

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   [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, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC3791]  Olvera, C., Nesser, P., and , "Survey of IPv4 Addresses in
              Currently Deployed IETF Routing Area Standards Track and
              Experimental Documents", RFC 3791, DOI 10.17487/RFC3791,
              June 2004, <http://www.rfc-editor.org/info/rfc3791>.

   [RFC4682]  Nechamkin, E. and J-F. Mule, "Multimedia Terminal Adapter
              (MTA) Management Information Base for PacketCable- and
              IPCablecom-Compliant Devices", RFC 4682,
              DOI 10.17487/RFC4682, December 2006,

   [RFC5965]  Shafranovich, Y., Levine, J., and M. Kucherawy, "An
              Extensible Format for Email Feedback Reports", RFC 5965,
              DOI 10.17487/RFC5965, August 2010,

   [RFC6430]  Li, K. and B. Leiba, "Email Feedback Report Type Value:
              not-spam", RFC 6430, DOI 10.17487/RFC6430, November 2011,

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol",
              RFC 6455, DOI 10.17487/RFC6455, December 2011,

   [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,

   [RFC6591]  Fontana, H., "Authentication Failure Reporting Using the
              Abuse Reporting Format", RFC 6591, DOI 10.17487/RFC6591,
              April 2012, <http://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, <http://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,

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   [RFC6652]  Kitterman, S., "Sender Policy Framework (SPF)
              Authentication Failure Reporting Using the Abuse Reporting
              Format", RFC 6652, DOI 10.17487/RFC6652, June 2012,

   [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, <http://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,

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://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,

   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
              December 2014, <http://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, <http://www.rfc-editor.org/info/rfc7457>.

   [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, <http://www.rfc-editor.org/info/rfc7525>.

   [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,

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   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <http://www.rfc-editor.org/info/rfc7799>.

   [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, <http://www.rfc-editor.org/info/rfc7858>.

   [RFCEdit]  https://www.rfc-editor.org/materials/abbrev.expansion.txt,
              "RFC Editor Abbreviation List".

   [Vocab]    https://portal.3gpp.org/desktopmodules/Specifications/
              SpecificationDetails.aspx?specificationId=558, "3GPP TR
              21.905 V13.1.0 (2016-06) Vocabulary for 3GPP

   [Web3GPP]  http://www.3gpp.org/technologies/95-keywords-acronyms,
              "3GPP Web pages on specific topics of interest".

Authors' Addresses

   Kathleen Moriarty
   Dell EMC
   176 South St
   Hopkinton, MA

   Phone: +1
   Email: Kathleen.Moriarty@dell.com

   Al Morton
   AT&T Labs
   200 Laurel Avenue South
   Middletown,, NJ  07748

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192
   Email: acmorton@att.com
   URI:   http://home.comcast.net/~acmacm/

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