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TLS/DTLS Content Provider Edge Server Split Use Case

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Daniel Migault , Kevin J. Ma
Last updated 2016-01-19
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Network Working Group                                         D. Migault
Internet-Draft                                                     K. Ma
Intended status: Standards Track                                Ericsson
Expires: July 22, 2016                                  January 19, 2016

          TLS/DTLS Content Provider Edge Server Split Use Case


   TLS as been designed to setup and authenticate transport layer
   between endpoints.

   A lot of applications are using TLS in order to set communications
   between the applications end points.

   As long as applications end points and transport end points were
   combined into the same host, application authentication could be
   combined with the transport authentication.

   As the current internet is decoupling the transport and application
   layers, such model may not be applicable anymore.  In other words,
   TLS authentication cannot be handled on behalf of the application

   This document describes use cases where the authentication of the
   transport layer differs from the authentication performed at the
   application layer.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 22, 2016.

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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Cloud Use Case  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Content Delivery Network Use Case . . . . . . . . . . . . . .   4
   5.  Authentication in Split Scenarios . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   TLS has been designed for end-to-end security between a TLS Server
   and a TLS Client.  As TLS is widely used to provide an authenticated
   channel between applications, the following models assumes that
   applications end points and connectivity end point are combined.  In
   that case, authentication of the connection end point and
   authentication of the application end point could be combined and
   assimilated as a single authentication.

   Such assumption for the TLS model may not be true especially in the
   current web architecture where application content is not anymore
   associated with the connection end point.  For example, Content
   Delivery Network are in charge of delivering content they are not
   necessarily owning.

   This document provides use case where authentication of of the TLS
   Server involves multiple parties or entities as opposed to a single

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   entity in the standard TLS model.  Such uses cases are designated a
   split use cases to point out that authentication is split between
   multiple entities.

2.  Terminology

   TLS Client:   The TLS Client designates the initiator of the TLS
         session.  The terminology is the one of [RFC5246].  The current
         document considers that the TLS Client and the application
         initiating the session are hosted on the same host.  If not
         they are hosted on the same administrative domain with a trust
         relation between the TLS Client and the application.  In other
         words, the client endpoint is considered to be a single entity
         as described initially in [RFC5246].

   TLS Server:   The TLS Server designates the endpoint of a TLS session
         initiated by the TLS Client.  This document considers that
         application end points and the TLS session end point my be
         hosted on different nodes, and may belong to different
         administrative domains.

   Edge Server:   The Edge Server designates a node that handles traffic
         for a Content Provider.  A TLS Client initiates a TLS session
         to authenticate a Content provider, but may be in fact served
         by a Edge Server that may belong to a different administrative

   Content Provider:   The owner of the content.  This is the entity
         requested by the application of the TLS Client.

   Content Delivery Network (CDN):   designates a organization in charge
         of managing delivery of a content on behalf of a Content
         Provider.  In most cases, the CDN is a different organization
         than the Content Provider.

3.  Cloud Use Case

   It is common that applications - like a web browser for example - use
   TLS to authenticate a Content Provider designated by a web URL and
   build a secure channel with that Content Provider.

   TLS provides end-to-end security between the two end points of the
   communication.  In our case, the two end points are the web browser
   also designated as TLS Client and the other end point is the TLS
   Server hosting the content.  When the TLS Server is the Content
   Provider, the web browser or the TLS Client can use TLS to set an
   authenticated and secure channel between the web browser and the
   Content Provider using TLS.  On the other hand, TLS can hardly be

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   used in a secure, scalable way when the TLS Server differs from the
   Content Provider.

   Suppose that the content of the Content Provider cannot be hosted by
   a single server.  This may be the case for example when a single
   server is not anymore sufficient to address all the load of the TLS
   Clients.  In this case, the load may be split between multiple
   instance of servers.  Similarly, a Content Provider may chose to
   place multiple instance of the servers with a limited subset of the
   content at different places in the network in order to avoid traffic
   to be conveyed through the whole data center or the content provider
   infrastructure.  In most of the cases, these instances of the servers
   are places at the edge of the infrastructure.  Another reason for
   having multiple instances may be that the content provider cannot
   host the entirety of its content on one single server.  In that case
   it may opt for hosting the content on various servers to which the
   application can be directly connected.

   When the Content Provider cannot present a single server, the web
   applications can connect to, it clearly appears that the Content
   Provider the application is trying to set an authenticated TLS
   session with and the TLS end point may differ.  In the latter case,
   the TLS end points are designated as Edge Servers.  These Edge
   Servers are used for connectivity and should operate transparently
   for the application.  In other words, the application requires that
   authentication of the application layer be performed at the transport

   In order to enable the web application to authenticate the Content
   Provider using TLS, two options may be considered:

   a):  Each Edge Server shares the authentication credential associated
        to the Content Provider.  This case results in each Edge Server
        usurping the identity of the Content Provider.

   b):  The authentication credentials of the Content Provider are kept
        secret, and any TLS session between a web application and an
        Edge Server involves some interaction between the Edge Server
        and the Content Provider.

   Section 5 evaluates these two possibilities.

4.  Content Delivery Network Use Case

   The Content Delivery Network Use case is similar as the Cloud use
   case exposed in Section 3.  The main difference is that the Edge
   Servers are not anymore under the responsibility of the Content
   provider.  Instead, the Content Provider has subscribed to a company

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   with a different administrative domain to manage the Edge Server on
   behalf of the Content Provider.

   In the case of Content Distribution Network Interconnection (CDNI)
   [RFC6707], it may also that the company with which the Content
   Provider has contracted may further delegate delivery to another CDN
   with which the Content Provider has no official business
   relationship.  Even if the Content Provider trusts the upstream CDN,
   and perhaps has strong legal contracts in place, it has no control
   over, and possibly no legal recourse against, the further downstream

   The same options as in Section 3 apply, but in case of sharing
   authentication credential of the Content Provider, these credentials
   are shared outside the administrative borders of the Content

5.  Authentication in Split Scenarios

   Access by the Edge Server to the private or secret information of the
   Content Provider may be performed either by sharing the information
   between the Content Provider and the Edge Servers or by using an
   interface between the Edge Servers and the Content Provider.

   Sharing secret information between the Content Provider and the Edge
   Servers increases the risk of leaking information.  The risk of
   leaking information exists as Edge Servers are exposed on the
   Internet which present a high surface of potential attack as
   illustrated for example by the Heartbleed attack [HEART].  More
   specifically, the Heartbleed attack uses a weakness of a software
   implementation to retrieve the private key used by the TLS server.
   Such attack would not for example has been so successful if the
   private key was not stored on the Edge Server.

   In addition, the risk increases with the number of Edge Servers and
   the number of organizations sharing these secrets.  In fact when the
   Edge Servers increases and are managed by multiple organizations, it
   becomes hard for the Content Provider to control the conformance of
   the Edge Servers to the security policies enforced by the Content
   Provider, or to detect when a leakage occurs.  At last, from a
   security point of view, this may be not acceptable the Content
   Provider .

   Currently an interface between the Edge Server and the Content
   Provider has not been standardized.  This may prevent a Content
   Provider to interact with multiple CDNs, or multiple CDNs to
   interoperate.  In addition, such interface may be used within a CDN
   in order to manage its own Edge Servers.  The absence of a standard

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   interface and the lack of interoperability may also result in the
   Content Provider sharing the confidential information with a third
   party organization.  This may be not acceptable in a security point
   of view.

6.  Security Considerations

   One motivation for split scenario is to avoid spreading
   authentication credentials of the Content Provider in multiple Edge
   Servers, and so to reduce the leak of such credentials.

   On the other hand, preventing the authentication credentials to be
   hosted on the Edge Servers do not necessarily prevent any leakage.
   In fact, the Edge Servers and the Content Providers are likely to use
   a specific channel that provide access to the credentials.  It is of
   primary importance to design this channel to avoid the Content
   Provider to reveal any information about the private key.  More
   specifically, even though a Edge Server may become corrupted or under
   the control of an attacker, the attacker should not be able to be
   able to disclose the authentication credentials.

7.  IANA Considerations

   There are no IANA considerations in this document.

8.  Acknowledgements

   Thanks are due for insightful feedback on this document to Robert
   Skog, Salvatore Loreto, John Mattson and Rich Salz.

9.  References

9.1.  Normative References

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
              RFC5246, August 2008,

   [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, DOI 10.17487/RFC6707, September
              2012, <>.

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9.2.  Informative References

   [HEART]    Codenomicon, "The Heartbleed Bug",

Authors' Addresses

   Daniel Migault
   8400 boulevard Decarie
   Montreal, QC   H4P 2N2

   Phone: +1 514-452-2160

   Kevin Ma J
   43 Nagog Park
   Acton, MA    01720

   Phone: +1 978-844-5100

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