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A Rationale for Fine-grained Intermediary-aware End-to-End Protocols

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Dan Druta , Thomas Fossati , Marcus Ihlar , Guenter Klas , Diego Lopez , Julian Reschke
Last updated 2014-10-27
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Network Working Group                                           D. Druta
Internet-Draft                                                      AT&T
Intended status: Standards Track                              T. Fossati
Expires: April 30, 2015                                   Alcatel-Lucent
                                                                M. Ihlar
                                                                 G. Klas
                                                                D. Lopez
                                                          Telefonica I+D
                                                         J. Reschke, Ed.
                                                        October 27, 2014

  A Rationale for Fine-grained Intermediary-aware End-to-End Protocols


   A tremendous growth in different uses of the Internet has led to a
   growing need to protect data sent over public networks, including
   data sent via HTTP.  Resorting to the use of end-to-end TLS and https
   for the majority of traffic looks at first like a most feasible
   response.  However, the more sophisticated the web architecture
   becomes as it goes beyond the simple client-server model, the more
   the end-to-end use of TLS shows its downside as it excludes the use
   of beneficial intermediaries like caches or proxies that provide
   instrumental services.  The need for greater privacy seems to collide
   with the equally growing desire for better end-to-end performance and
   user experience.  As an example, the use of TLS and https often
   appears to maximise the benefit for the first but not the benefit for
   the combination of both.

   This document describes this dilemma and lays out a number of
   objectives of what should ideally be achieved, namely catering for
   sufficient security and privacy whilst providing users with the
   opportunity to make use of intermediaries' services where considered
   beneficial.  We then introduce a number of characteristics potential
   solutions could have, with the hope that those will steer us towards
   suitable protocol mechanisms and data formats.  End-to-end protocols
   which are aware of intermediaries should enable users and/or content
   providers to exercise fine-grained control over what intermediaries
   shall be able to do and what exposure to data or metadata they shall
   be permitted to get.  The document then highlights anticipated
   benefits to key stakeholders like users, content providers and
   intermediaries.  As elements like object security can play a useful
   role, we encourage the analysis of related pieces of work in order to

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   discern their applicability, limitations, and coverage of use cases.
   This will allow us to frame an overall architecture and motivate more
   detailed work on protocols and mechanisms in the future.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 30, 2015.

Copyright Notice

   Copyright (c) 2014 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
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   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Objectives . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Characteristics of Solutions . . . . . . . . . . . . . . . . .  6
   4.  Benefits for the content provider, for the users, for the
       intermediaries . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Analysis of Related Work . . . . . . . . . . . . . . . . . . .  9
   6.  Architectural Considerations . . . . . . . . . . . . . . . . . 10
   7.  Analysis of the Impacts on HTTP/2  . . . . . . . . . . . . . . 10
   8.  Analysis of the Impacts on TLS . . . . . . . . . . . . . . . . 10
   9.  Impacts on the current browser architecture  . . . . . . . . . 10
   10. Impacts on the existing deployment / how to make this
       proposal coexist with the current  . . . . . . . . . . . . . . 10
   11. Privacy Impact . . . . . . . . . . . . . . . . . . . . . . . . 10
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
   14. Informative References . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   In the last decade, the generalization of network access, the cloud
   and the ubiquity of the Web as an application platform has translated
   into an unprecedented increase in the use of the Internet,
   facilitated by the development of new web standards and the
   innovations in mobile technologies.  With this growth in use, there
   has been an increased amount of personal data being sent over multi
   hop public links.

   In order to protect the integrity and confidentiality of the online
   transactions, HTTP traffic can be secured with transport layer
   security using https.  While https is great for e-commerce and
   banking and while there is a sense of understanding in the user
   community around the secure nature of https, using TLS and https for
   the majority of the traffic has performance and functional drawbacks,
   mainly because the HTTP session is encrypted as a whole.

   Looking from the privacy and security perspective, it is clear that
   users must be aware if and when an intermediary node is intercepting
   their traffic and they have the right to continue or demand higher
   levels of privacy by encrypting what they deem to be sensitive
   information.  The privacy threshold depends on user's tolerance and
   the trust they put in the intermediary's reputation, as well as
   whether the user is the ultimate consent authority for a given
   connection: for example a parent or employer may take that role for a
   connection used by a child or employee.

   Modern web architecture involves sophisticated caching schemes that
   involve fetching various objects (images, libraries, etc.) from
   various locations in the path to avoid latency and improve the
   overall user experience while reducing bandwidth use.  This is an
   important aspect especially in the developing countries, remote
   locations and in general areas that lack fast network infrastructure.

   Issues thus arise from the clash of two trends: One is towards
   enhanced privacy calling for integrity, confidentiality and
   anonymity.  The other one is towards improved performance and lower
   latency, calling for caching, compression, and adaptability.

   This is also reflected in the views of important stakeholders.  Users
   want to make informed decisions in regards to whom they trust with
   their data.  They also want to have control over what data they share
   with whom.

   Web site owners and content providers on the other hand are keen to
   get the most cost efficient and reliable way to deliver information
   and services to their users and customers, while preserving their

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   confidentiality, protecting their privacy and the integrity of their

   As different entities seek to meet the requirements of their
   stakeholders, they sometimes apply solutions which generate
   conflicts.  Clients act on behalf of end users and solutions may
   include local caches and browser proxies.  Servers act on behalf of
   content providers and solutions may include the use of CDNs and
   reverse proxies.  Intermediaries operated by communication service
   providers and network operators act on behalf of users and/or content
   providers and solutions include means for access network optimization
   and content filtering.

   In above context, the use of TLS and https looks like a "black and
   white approach", or an "all or nothing" approach which doesn't lend
   itself to resolving above-mentioned conflicts.  The question arises:
   Can "color be added"?

   TLS is a client server protocol and it serves its purpose perfectly
   in many client-server scenarios and use cases.  But then the web has
   evolved to become a mesh.  Average traffic flows now involve various
   intermediaries between clients and servers.  They add value by
   performing different functions including multiple levels of

   The application of TLS forces point-to-point flows which cuts out
   intermediaries and can lead to significant drawbacks.  It reduces
   e.g. the optimization options which translates into increasing
   traffic volumes in access networks, higher latency and overall
   decreasing quality of experience for users.

   It can be observed that ignoring the role of intermediaries on the
   Internet does not necessarily make the Internet more secure.  In
   fact, in some cases it forces various parties to break the TLS
   promise of e2e integrity and confidentiality in order to meet their
   legal obligations (enterprises).

   We suggest the solution to the challenge lies in "adding color".  An
   example of this are fine-grained intermediary-aware end-to-end

   Assuming the existence of such a fine-grained protocol, the following
   benefits could be imagined which leads to satisfying the justified
   needs of multiple stakeholders:

   The ability to atomically encrypt objects or even HTTP frames should
   support this sophisticated caching mechanisms while allowing content
   providers to avoid distributing their server key material across the

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   network nodes and prevent the risk of compromising their security.

2.  Objectives

   Given the short description of the problem above, the following
   objectives can be derived.

   1.  To improve security and user-controlled privacy.

   2.  To minimize passive interception and man in the middle attacks.

   3.  To allow the client (user) and the server (content provider) to
       negotiate what and whom they want to give (or not) visibility
       into their traffic flows.

   4.  To enable multiple levels of optimization that don't conflict
       with each other and either meet all parties expectations or
       maximise the benefit to as many involved parties as possible.

   In a world of TLS and https only, it is difficult to achieve in
   particular objectives 3. and 4.

   The challenge therefore is in finding mechanisms or protocols which
   meet objectives 1. and 2. (e.g. in the way TLS is delivering against
   those objectives) AND simultaneously provide the added flexibility to
   leverage the services of 3rd party intermediaries located between
   client and origin server.

3.  Characteristics of Solutions

   From above, one can draw some conclusions about the characteristics
   possible solutions or new protocols may have to show.  Below is a
   non-exhaustive list.  A new fine-grained intermediary-aware end-to-
   end protocol may need to feature:

   1.  a mechanism to enable users to choose their preferred level of
       privacy, adequate for a particular context and use case.  The
       context may be determined by the presence or absence of
       particular intermediaries or proxies which offer particular
       services (e.g. caching, data compression etc.).

   2.  mechanisms that enable certain communication data to be exchanged
       securely, whereby the end user shall be able to select the set of
       security services deemed adequate for a particular communication
       context (e.g. confidentiality, data integrity, entity
       authentication etc.).

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   3.  mechanisms that enable the end user to select which communication
       data shall be subject to particular security services (like
       confidentiality, data integrity etc.).  Note that this might be
       all application level data transferred between server and client,
       or it might be a subset of application level data.  This refers
       to the notion of "fine-grained" control.

   4.  mechanisms that protect against passive interception and man-in-
       the-middle attacks.

   5.  mechanisms that allow the two ultimate communication end points,
       namely client and origin server, to negotiate whether and if so
       which intermediaries shall be permitted to play a role in
       delivering application data from origin server to client given
       particular end user expectations, requirements and preferences,
       and information about the status of the network between client
       and server.  This refers to the notion of "intermediary-aware
       end-to-end protocol".

   6.  mechanisms that allow end users or origin server or both to
       determine in real-time which traffic optimizations are available
       at the time of communication setup.

   7.  mechanisms that allow end users or origin servers or both to
       eventually select zero or more optimizations to be applied to
       traffic flows between origin server and client.

   8.  mechanisms that allow the simultaneous or sequential application
       of optimizations such that those optimizations on traffic and
       traffic flow don't conflict with each other.

   As said, above list is not exhaustive and additional characteristics
   may be either required or useful.

   The intent of this draft is not to introduce a solution yet.
   However, it may help to consider possible elements which might play a
   role in any solution.  One element is "object security".

4.  Benefits for the content provider, for the users, for the

   An object security approach will allow the different parties to
   establis end-to-end and hop-by-hop security mechanisms to different
   data and metadata elements, and therefore address what can be seen as
   conflicting requirements in terms of optimization and security

   The following benefits will arise for the different stakeholders:

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   Content providers:

   o  Can select the type of security service that is optimal and
      sufficient for particular types of content: e.g. confidentiality,
      integrity protection, entity authentication etc.

   o  Can select which parts of their content shall be secured or not
      and how content shall be securely retrievable.

   o  Can increase their confidence in secure temporary content storage
      during delivery through encrypting/signing sensitive content

   o  Can leverage the business services of 3rd parties (intermediaries)
      through enabling the intermediaries to perform value-added
      services.  Content providers may outsource particular tasks (like
      caching, or offering higher security level to users) to

   o  When using the services of content delivery networks, can benefit
      from faster, optimised delivery over the "last mile" (as seen from
      the perspective of a content delivery network).  Content delivery
      networks can optimise delivery on behalf of content providers over
      the first and middle mile, however they often rely on other ISPs
      and mobile network operators to deliver content over the last
      mile.  Intermediaries in the last mile can optimise traffic


   o  Are able to enjoy sufficient privacy and security as dictated by
      different use cases and equally their personal preferences (e.g.
      protection from traffic analysis, integrity of content).

   o  Can benefit from value-added services delivered by intermediaries
      on behalf of content providers.

   o  Can have access to services offered by intermediaries which
      enhance end user quality of experience (e.g. malware detection,
      parental controls).

   o  Can access web resources and services with lower latency and
      better response times (e.g. through intermediaries performing
      video pacing or traffic engineering to avoid congestion on
      particular networks).


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   o  Can play their specific roles in content delivery and
      communication on behalf of content providers, like

      *  Caching of content on behalf of content providers

      *  Optimisation of content for optimal delivery on behalf of
         content providers

      *  Video pacing on behalf of content providers.

   o  Can provide value-added services on behalf of users like parental
      control, malware detection etc.

   o  Can optimise content delivery and data communication within a
      network they are associated with or control e.g. through traffic
      engineering and traffic management by taking into account the
      inherent needs of content types and the explicit real- and non-
      real-time requirements of content providers and content delivery
      networks.  Thereby, intermediaries contribute to an improved "end-
      to-end" user experience in the interest of both users and content

      *  Intermediaries are enabled to perform congestion management and
         can therefore reduce latency and response times.

   o  Can meet regulatory requirements as they may prevail in particular
      jurisdictions through an approach which is more open and
      transparent to both users and content providers, and which may be
      in the national interest.

5.  Analysis of Related Work

   The concept of object security is not something new, several
   approaches targeted at different application areas exist today, and
   we can even root them at the original S/MIME proposal ([RFC5751]).

   As one of our first tasks, we intend to perform a detailed analysis
   of this related work, producing a list of the gaps of each technology
   solution in the scenarios we foresee.  In particular, we have already
   identified at least a couple of such related work:

   o  JOSE, which stands for "JSON Object Signing and Encryption".  It
      is a series of standards produced by the IETF under the JOSE
      charter (<>) offering
      encryption, digital signatures, and Message Authentication Codes

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   o  Subresource Integrity ([SRI]), a W3C specification defining
      mechanisms by which user agents may verify that a fetched resource
      has been delivered without unexpected manipulation.

6.  Architectural Considerations

   The purpose of an object security architecture is to be able to
   provide more flexible security services than strict end-to-end
   encryption.  A content owner should be able to express what security
   levels different objects should be associated with.

   Such an architecture needs to define two types of logical channels
   between end-points.  One channel is strictly end-to-end encrypted
   where sensitive data is transferred between end points without the
   risk of third-party access.  The second channel is more relaxed in
   allowing third-party nodes be part of the flow (i.e hop-by-hop
   encrypted channel).  The amount of information exposed in the second
   channel is determined by the content provider alone or in agreement
   with the end-user.

   There are several ways to design an architecture that fulfills these
   requirements.  An important question to analyze is whether an object
   security architecture should be designed at the application layer or
   further down the stack as an alternative to TLS.

7.  Analysis of the Impacts on HTTP/2

   [[anchor7: TBD]]

8.  Analysis of the Impacts on TLS

   [[anchor9: TBD]]

9.  Impacts on the current browser architecture

   [[anchor11: TBD]]

10.  Impacts on the existing deployment / how to make this proposal
     coexist with the current

   [[anchor13: TBD]]

11.  Privacy Impact

   [[anchor15: TBD]]

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12.  Security Considerations

   [[anchor17: TBD]]

13.  Contributors

   The following people are not listed as authors, but contributed
   significantly to the discussions leading to this document: Liliana
   Dinale, Vijay Gurbani, Mike Jones, Eliot Lear, Salvatore Loreto, John
   Mattsson, Sanjay Mishram, Robert Moskowitz, Kevin Smith, Dan Wing.

14.  Informative References

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

   [SRI]      Braun, F., Akhawe, D., Weinberger, J., and M. West,
              "Subresource Integrity", W3C Working Draft WD-SRI-
              20140318, March 2014,

              Latest version available at <>.

Authors' Addresses

   Dan Druta


   Thomas Fossati


   Marcus Ihlar


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   Guenter Klas


   Diego R. Lopez
   Telefonica I+D


   Julian F. Reschke (editor)
   greenbytes GmbH


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