



Network Working Group                                      M. Nottingham
Internet-Draft
Intended status: Informational                                   J. Hall
Expires: February 25, 2016                                           CDT
                                                            N. ten Oever
                                                               Article19
                                                              W. Seltzer
                                                                     W3C
                                                         August 24, 2015


                   User Impact of Transport Metadata
             draft-nottingham-transport-metadata-impact-00

Abstract

   This draft attempts to identify potential impacts associated with
   new, extensible metadata facilities in Internet protocols, and
   suggests possible mitigations.  Its goal is to have the discussion of
   these tradeoffs up-front, rather than after the development of such
   mechanisms.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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

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

   This Internet-Draft will expire on February 25, 2016.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



Nottingham, et al.      Expires February 25, 2016               [Page 1]

Internet-Draft          Transport Metadata Impact            August 2015


   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.  Potential Impact  . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Security and Privacy  . . . . . . . . . . . . . . . . . .   3
     2.2.  Network Neutrality  . . . . . . . . . . . . . . . . . . .   4
   3.  Possible Mitigations  . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Constrained Vocabulary  . . . . . . . . . . . . . . . . .   4
     3.2.  Transparency  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  Informative References  . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Recently, there has been an increasing amount of discussion in the
   IETF about adorning protocol flows with metadata about the network's
   state for consumption by applications, as well as that of the
   application in order to inform decisions in the network.  For
   examples, see [I-D.nottingham-gin],
   [I-D.sprecher-mobile-tg-exposure-req-arch] and
   [I-D.hildebrand-spud-prototype].

   These discussions are being at least partially motivated by the
   increasing use of encryption, both in deployment (thanks to the
   Snowden revelations) and standards (thanks in some part to [RFC7258],
   [IAB-confidentiality], and [TAG-securing-web]); while it's becoming
   widely accepted that networks don't have legitimate need to access
   the content of flows in most cases, they still wish to meet certain
   use cases that require more information.

   For example, networks may wish to communicate their state to
   applications, so that link limitations and transient problems can be
   accounted for in applications, by doing things like degrading (or
   improving) video streaming quality.

   Applications also need to give enough information to networks to
   enable proper function; e.g., packets in UDP flows need to be
   associated to be able to cleanly transit NAT and firewalls.  See
   [I-D.trammell-stackevo-newtea] and [I-D.hardie-spud-use-cases] for
   more discussion.




Nottingham, et al.      Expires February 25, 2016               [Page 2]

Internet-Draft          Transport Metadata Impact            August 2015


   At the same time, it has been widely noted that "metadata" in various
   forms can be profoundly sensitive information, particularly when
   aggregated into large sets over extensive periods of time.

   Indeed, much of the effort in combatting pervasive monitoring (as per
   [RFC7258]) has focused on minimizing metadata in existing, known
   protocols (such as TLS and HTTP).

   Any new metadata facility, then - whether it be introduced to an
   existing protocol, or as part of a new one - needs to be carefully
   scrutinized and narrowly tailored to conservatively emit metadata.
   Of particular concern is an observed trend towards arbitrarily
   extensible metadata.

   This draft attempts to identify potential impacts associated with new
   metadata facilities in Internet protocols, and suggest possible
   mitigations.  Its goal is to initiate a discussion of these tradeoffs
   up-front, rather than waiting until after the development of such
   mechanisms.

   Adding metadata to protocols is not an inherent harm - i.e., there
   are some legitimate uses of metadata, particularly if it eases the
   adoption of encrypted protocols or aligns well with both the
   interests of users and service or network operations, e.g., traffic
   management on mobile networks.  However, the balance between the
   interests of constituents like end users, content providers and
   network operators needs to be carefully considered.

2.  Potential Impact

2.1.  Security and Privacy

   It's been established [Injection] that many network operators inject
   HTTP headers into requests, in order to identify their customers
   using a unique identifier, thereby allowing "third-party advertisers
   and websites to assemble a deep, permanent profile of visitors' web
   browsing habits without their consent."  [X-UIDH]

   In doing so, these networks are taking advantage of a relatively
   unconstrained extension point in the HTTP protocol - header fields.
   While HTTP header fields do require registration [RFC3864], the
   requirements are lax, and fields are often used without registration,
   because there is no technical enforcement of the requirements, due to
   HTTP's policy of ignoring unrecognized header fields [RFC7230].

   HTTP header fields can be made a protected end-to-end facility by
   using HTTPS, avoiding the risk of such injection.  A new transport




Nottingham, et al.      Expires February 25, 2016               [Page 3]

Internet-Draft          Transport Metadata Impact            August 2015


   metadata facility that explicitly allows any node on the path to add
   arbitrary metadata cannot.

   Well-intentioned metadata can also put the user at substantial risk
   without careful consideration.  For example, if a Web browser
   "labels" flows based upon what they contain (e.g., "video", "image",
   "interactive"), an observer on the network path - including pervasive
   ones - can more effectively perform traffic analysis to determine
   what the user is doing.  Similarly, metadata adornment might reveal
   sensitive information; for example the Server Name Indicator (SNI) in
   the TLS handshake would reveal if a web visitor intends to go to
   "bannedcontent.github.com" versus "kitties.github.com".

   Standardizing an extensible transport metadata mechanism could also
   trigger various jurisdictions to define and require insertion of in-
   band metadata, an extension of current practices [AU-data-retention].
   While the IETF would not be directly responsible for such an outcome,
   it is notable that in the past we've explicitly said we won't serve
   conceptually similar use cases [RFC1984].

2.2.  Network Neutrality

   There is obvious potential for network neutrality impact from a
   mechanism that allows networks to communicate with endpoints about
   flows.

   For example, if a network can instruct content servers to throttle
   back bandwidth available to users for video based upon a commercial
   arrangement (or lack thereof), the network can achieve their goals
   without directly throttling traffic, thereby offering the potential
   to circumvent a regulatory regime that's designed to effect network
   neutrality.

   While the IETF has not take as firm a stance on network neutrality as
   it has for Pervasive Monitoring (for good reasons, since network
   neutrality problems are at their heart a sign of market failure, not
   a technical issue), new metadata facilities that enable existing
   regulatory regimes - thereby upsetting "the tussle" - must be
   carefully considered.

3.  Possible Mitigations

3.1.  Constrained Vocabulary

   Much of the potential for harm above comes about because a transport-
   level metadata mechanism effectively becomes a side channel for
   arbitrary data, for use by any node on the path.  The risks of




Nottingham, et al.      Expires February 25, 2016               [Page 4]

Internet-Draft          Transport Metadata Impact            August 2015


   questionable use could be mitigated by constraining the data that's
   allowed in this side channel.

   In other words, if the network doesn't have a means of inserting a
   unique identifier for customers, they won't be able to do so.  If
   notification of constrained network conditions takes place using
   well-defined terms, regulatory regimes can be adjusted to achieve
   desired outcomes.  And, information about application semantics can
   be carefully vetted for security considerations before being included
   in transport metadata.

   One way to technically enforce such constraints would be to require
   nodes to silently drop non-standard metadata.  Another would be to
   not make metadata extensible at all.

   Naturally, this would constrain the ability of networks and
   applications to add new terms to metadata, thereby requiring more
   careful thought to go into the metadata that is standardised "up
   front."

3.2.  Transparency

   Many proposals for transport metadata assert that it will be
   encrypted, to improve security.  While well-intentioned, it also
   creates an opaque side channel with a third party (the first and
   second being the endpoints).

   The effect of of such designs should be carefully considered before
   standardisation; it may be that the community is better served by
   keeping this metadata "in the clear", albeit possibly with some form
   of authentication and integrity available (or required).

4.  Security Considerations

   This document describes security and privacy aspects of metadata
   adornment to internet protocols that protocol designers should
   consider.

5.  Informative References

   [AU-data-retention]
              Keane, B., "Your guide to the data retention debate: what
              it is and why it's bad", March 2015,
              <http://www.crikey.com.au/2015/03/18/your-guide-to-the-
              data-retention-debate-what-it-is-and-why-it's-bad/>.






Nottingham, et al.      Expires February 25, 2016               [Page 5]

Internet-Draft          Transport Metadata Impact            August 2015


   [I-D.hardie-spud-use-cases]
              Hardie, T., "Use Cases for SPUD", draft-hardie-spud-use-
              cases-01 (work in progress), February 2015.

   [I-D.hildebrand-spud-prototype]
              Hildebrand, J. and B. Trammell, "Substrate Protocol for
              User Datagrams (SPUD) Prototype", draft-hildebrand-spud-
              prototype-03 (work in progress), March 2015.

   [I-D.nottingham-gin]
              Nottingham, M., "Granular Information about Networks",
              draft-nottingham-gin-00 (work in progress), July 2014.

   [I-D.sprecher-mobile-tg-exposure-req-arch]
              Jain, A., Terzis, A., Sprecher, N., Swaminathan, S.,
              Smith, K., and G. Klas, "Requirements and reference
              architecture for Mobile Throughput Guidance Exposure",
              draft-sprecher-mobile-tg-exposure-req-arch-01 (work in
              progress), February 2015.

   [I-D.trammell-stackevo-newtea]
              Trammell, B., "Thoughts a New Transport Encapsulation
              Architecture", draft-trammell-stackevo-newtea-01 (work in
              progress), May 2015.

   [IAB-confidentiality]
              Internet Architecture Board, "IAB Statement on Internet
              Confidentiality", November 2014,
              <http://www.iab.org/2014/11/14/
              iab-statement-on-internet-confidentiality/>.

   [Injection]
              Ammari, N., Bjo&#776;rksten, G., Micek, P., and D.
              Olukotun, "The Rise of Mobile Tracking Headers: How Telcos
              Around the World Are Threatening Your Privacy", August
              2015, <https://www.accessnow.org/blog/2015/08/17/read-our-
              new-report-on-the-troubling-rise-of-tracking-headers-
              worldwide2>.

   [RFC1984]  IAB and , "IAB and IESG Statement on Cryptographic
              Technology and the Internet", RFC 1984, DOI 10.17487/
              RFC1984, August 1996,
              <http://www.rfc-editor.org/info/rfc1984>.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              DOI 10.17487/RFC3864, September 2004,
              <http://www.rfc-editor.org/info/rfc3864>.



Nottingham, et al.      Expires February 25, 2016               [Page 6]

Internet-Draft          Transport Metadata Impact            August 2015


   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing", RFC
              7230, DOI 10.17487/RFC7230, June 2014,
              <http://www.rfc-editor.org/info/rfc7230>.

   [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>.

   [TAG-securing-web]
              W3C Technical Architecture Group, "Securing the Web",
              January 2015, <http://www.w3.org/2001/tag/doc/web-https>.

   [X-UIDH]   Hoffman-Andrews, J., "Verizon Injecting Perma-Cookies to
              Track Mobile Customers, Bypassing Privacy Controls",
              November 2014, <https://www.eff.org/deeplinks/2014/11/
              verizon-x-uidh>.

Authors' Addresses

   Mark Nottingham

   Email: mnot@mnot.net
   URI:   https://www.mnot.net/


   Joseph Lorenzo Hall
   CDT

   Email: joe@cdt.org
   URI:   https://cdt.org/


   Niels ten Oever
   Article19

   Email: niels@article19.org
   URI:   https://www.article19.org/


   Wendy Seltzer
   W3C

   Email: wseltzer@w3.org
   URI:   http://wendy.seltzer.org/






Nottingham, et al.      Expires February 25, 2016               [Page 7]
