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Versions: 00

Network Working Group                                            R. Peon
Internet-Draft                                               Google, Inc
Intended status: Informational                              June 8, 2012
Expires: December 10, 2012


                     Explicit Proxies for HTTP/2.0
                     draft-rpeon-httpbis-exproxy-00

Abstract

   This document describes a method for connecting to a proxy via a
   secure channel, allowing, disallowing, and detecting any transforms
   that the proxy may perform, and allowing the proxy to connect via
   secure channel to another site on the user's behalf.

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 December 10, 2012.

Copyright Notice

   Copyright (c) 2012 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
   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.




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Table of Contents

   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  What it looks like today . . . . . . . . . . . . . . . . . . .  4
   4.  Where we would like to be  . . . . . . . . . . . . . . . . . .  4
   5.  Problems with end-to-end privacy?  . . . . . . . . . . . . . .  5
   6.  Proposed Solution: Use Explicit Proxies  . . . . . . . . . . .  6
   7.  Mixed trust mode . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  Rejected Alternatives  . . . . . . . . . . . . . . . . . . . .  9
   9.  Impact on other areas of the protocol  . . . . . . . . . . . . 10
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   11. Requirements Notation  . . . . . . . . . . . . . . . . . . . . 11
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   13. Normative References . . . . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12



































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1.  Overview

   It has been proposed that a secure channel be utilized for all
   HTTP/2.0 traffic coming from users using browsers.  As a first order
   effect, this would obviously improve security, but it could have the
   second order effect of banishing all communication over any secure
   channel for lack of a mechanism to allow the owners of the network to
   apply desired policies to the messaging going on within it.  Another
   second order effect could be user selection away from this protocol
   if it doesn't meet their performance expectations.  This document
   proposes mechanisms intended to ameleoriate these issues.  This
   document does not exhaustively cover configuring a proxy in a
   browser.


2.  Definitions

         user-agent: The program or device which a human interacts with
         directly and which typically initiates the transport layer
         connection or session

         client: Synonym for user-agent

         user: The human using the user-agent

         server: The computer or device which typically accepts a
         connection and serves data

         content-provider: The server to which the user-agent ultimately
         wishes to speak

         configured-proxy: The entity to which the user-agent is
         explicitly configured to speak and which the user-agent expects
         will connect to the content-provider on the user-agent's behalf

         trusted-proxy: A configured-proxy to which the user-agent has
         been configured to give decryption key material

         caching-proxy: A configured-proxy to which the user-agent has
         NOT been conigured to give decryption key material

         end-to-end: From the user-agent to the content-provider

         point-to-point: Between any two pairs of adjacent entities.  If
         the entities are user-agent and content-provider, this is also
         end-to-end, but for any other pair of entities, it is only
         point-to-point.




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         secure-hash: A cryptographic hash resistent to preimage and
         collision attacks, whether as part of a hash tree (e.g.  Merkle
         tree), hash list, etc.


3.  What it looks like today

   Today:

         Using TLS [RFC5246] over port 443 is often the exception rather
         than the rule.

         Many users use radio-based devices which transmit data
         effectively in the clear, allowing their credentials and
         identity to be stolen.

         Many networks seem to leave the traffic on port 443 untouched
         and unblocked, likely as a result of both the importance of the
         data and the relative rarity of communications using TLS.

         Entities which need to inspect traffic on port 443 today are
         forced to either block port 443 or to deploy an intercepting
         proxy and install root certs on all devices which may use the
         network.  In the latter case, the deployed proxy impersonates
         both the content-provider to the user-agent, and the user-agent
         to the content-provider.  Though there is work to allow users
         to detect these situations [DANE], support is not widespread.

         Users are likely to see both beneficial and detrimental
         behavior as a result of transparent proxies.

         Many, if not most, mobile devices using cellular networks use
         proxies

         Users and sites have only one mechanism for specifying point-
         to-point security policy for HTTP [RFC2616], which is the
         scheme of the URI identifying any particular resource.


4.  Where we would like to be

   In the future:

         A user's communications should use a channel which is point-to-
         point secure by default for all communications.






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         Users should be able to opt-out of communicating sensitive
         information over a channel which is not end-to-end private.

         Only proxies which are known to and configured by the user
         should be allowed to intercept communications between the user
         and the content-provider.

         User-agents and servers should know when a proxy is interposed
         in the communications channel.

         User-agents should be able to detect when content requested
         with an https scheme has been modified by a proxy.

         Caching should still be a service which can be provided by
         entities other than the server or user-agent.

         Caches, when allowed, should be exceedingly difficult to
         poison.

         A set of signaling semantics should exist which allows the
         content-provider and the user to have the appropriate level of
         security or privacy signaled per resource.


5.  Problems with end-to-end privacy?

   Entities may wish to have a proxy interposed in communication for a
   number of reasons including (but not limited to):

      Looking for and blocking malware

      Filtering for content by size, type, or subject matter

      Provide caching services so as to improve the user experience

   Unfortunately, if communication is to be done in majority or
   completely using end-to-end privacy, then none of the above use-cases
   are possible without installing root certs on users' devices.  There
   are several possible consequences for having only end-to-end privacy:

         It may become common for entites to install root certs on
         users' devices, and users may become accustomed to doing this,
         even on their personaly owned devices.  This could cause a
         breach of all trust-chains, and could reduce aggregate
         security.






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         Entities which own networks may decide to block port 443, else
         face noncompliance of policy or law.  This would obviously
         reduce aggregate security.

         Clients at the end of long, thin pipes may decide that speed
         matters more than security, and disable use of the new, secure
         protocol.  This would also obviously decrease aggregate
         security.

   The assumptions and potential consequences in this section should be
   carefully deliberated.


6.  Proposed Solution: Use Explicit Proxies

   Since failing to allow for some kind of interception technique may
   reduce aggregate security, it is suggested we design for and allow
   explicit proxies which may examine contents as they pass by.  This is
   not something to be done lightly, and so we must be careful to allow
   the user-agent to select an appropriate level of trust.  We must also
   provide for a fallback in cases where the proxy or server does not
   adhere to this proposal so that in the worst case we get what we have
   today.

   For the purpose of this document, it is assumed that the user locates
   a piece of paper upon a wall and reads it, typing these proxy
   settings into a configuration field for their user-agent.  This is
   obviously not the only possible configuration mechanism, but it may,
   sadly, be the most secure.  It is assumed that alternate distribution
   techniques may be discussed.

   For HTTPS schemes, if a proxy is configured:

         The user-agent MUST indicate to the content-provider that it is
         going through a proxy via the tunnel as the first bit of
         information presented.

         If a link in an HTML [RFC2854] document includes a secure-hash
         of the data, e.g. <a href="https://foo.bar.com/baz"
         hash=0ACC827F19F36BA>, and the link was provided in a secure
         manner (e.g. over an end-to-end communications channel that
         includes integrity checks), then the user-agent MAY request the
         indicated resource directly from the explicitly configured
         proxy.  The configured proxy MAY serve the data from its cache,
         but it MUST NOT modify the content in any way.  The user-agent
         MUST reject any received data if is unable to verify its
         integrity or if the secure-hash does not match the hash over
         the provided data.  The presence of the secure-hash is, itself,



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         signals that the content may be fetched in a non-private
         channel.  RFC6249 [RFC6249] provides some descriptions of
         cryptographic-hash implementations.

         The above need not be the only mechanism for providing signals
         that data can be served via a cache, but the data MUST always
         be verifiably unmodified.  As an example, other mechanisms for
         providing secure-hashes could be:

               The URI syntax [RFC3986] could be modified to include a
               hash of the contents.

               A signed manifest may be sent which includes one or more
               secure-hashes of byte-ranges of the data, either fetched
               via a separate resource or sent in-band.  The signature,
               would, of course, have to be validated before the secure-
               hashes were to be trusted, and before any requests were
               sent in a non end-to-end private channel.  RFC6249
               [RFC6249] provides some descriptions of such mechanisms.
               Bittorrent provides another example [BITTORRENT].

               Within the TLS Tunnel, frames may be sent describing the
               secure-hash of a byte-range of the data, by request from
               the user-agent.  Multiple secure-hashes may be returned
               if the byte-range mapping on the server differs from that
               requested by the client.  This alternative is most
               interesting for its ability to describe dynamically
               generated data (such as live video) safely and in a way
               that can be consumed by the client in a closer-to-real-
               time manner, and for supporting range-requests.  If
               implemented in a protocol similar to SPDY [SPDY], this
               could be accomplished with HEADER frames or equivalent.

         If the user agent has no means of verifying the data is
         unmodified, the user-agent either MUST tunnel through the proxy
         by doing a CONNECT with a TLS tunnel, or the user-agent MUST
         reuse a previously-created tunnel offering the same security.
         If the proxy refuses this communication the user-agent MUST
         attempt a connection directly to the content-provider, avoiding
         the proxy.

   We're proposing that user-agents allow for two levels of security for
   any proxy:

      Trusted Proxy - all data sent and received is inspected by the
      proxy





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      Caching Proxy - only data which could be served from the cache is
      inspected by the proxy

   It is also possible for a user-agent to use a proxy in both
   configured and trusted-proxy modes.  This document does not include
   mechanisms for signaling this.

   In the case where the proxy connects to the content-provider using a
   secure, multiplexed connection, the following diagram and description
   would apply:

    Anne = the client or user-agent
    Bob = point-to-point secure multiplexed connection from Anne<->Chris
    Chris = the proxy
    Don = point-to-point secure multiplexed connection from Chris<->Ed
    Ed = the content-provider


       Client                     Proxy            Content-provider
        |                           |                            |
        | /==spdy-connection=Bob==\ | /==spdy-connection=Don==\  |
       Anne   --connect-stream--  Chris  --connect-stream--     Ed
          \=======================/   \=======================/




   In the case where the user-agent has been configured with Chris as a
   trusted-proxy, either Anne's connect-stream MUST use either a null-
   cipher, or Anne MUST provide the decryption key material to Chris
   immediately after tunnel establishment, and before any data traverses
   the tunnel.
   In the case where the user-agent has been configured with Chris as a
   caching proxy, Anne's connect-stream SHOULD NOT use the null cipher,
   and Anne SHOULD NOT provide the decryption key material to Chris.

   In *all* cases, the user-agent must indicate that it is traversing a
   proxy within the connect-tunnel, and indicate whether the proxy is a
   trusted-proxy or caching-proxy.

   In the case where the proxy cannot use a secure, multiplexed
   connection when connecting to the content-provider, the following
   diagram and description would apply.  It is hoped that this case will
   never be selected as a spec-compliant implementation for forward
   proxies as it offers significantly less scalability than the option
   proposed above.





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    Anne = the client or user-agent
    Bob = point-to-point secure multiplexed connection from Anne<->Chris
    Chris = the proxy
    Ed = the content-provider


       Client                     Proxy          Content-provider
        |                           |                        |
        | /==spdy-connection=Bob==\ |                        |
       Anne  --connect-stream--  Chris <--connect-stream--> Ed
          \=======================/




   In both trusted-proxy and caching-proxy cases, Anne must select a
   non-null cipher for use in the tunnel.  In both the trusted-proxy and
   caching-proxy cases, the proxy simply forwards the tunnel's bytes to
   Ed and vice-versa.  In the case where the user-agent has been
   configured with Chris as a trusted-proxy, Anne MUST provide the
   decryption key material to Chris immediately after tunnel
   establishment, and before any data is sent along the tunnel.
   In the case where the user-agent has been configured with Chris as a
   caching-proxy, Anne SHOULD NOT provide the decryption key material to
   Chris.  If Anne selected a null-cipher in this case, Chris MUST
   reject the connection, forcing Anne to attempt to fallback on a
   separate connection.

   In *all* cases, the user-agent must indicate that it is traversing a
   proxy within the connect-tunnel, and indicate whether the proxy is a
   trusted-proxy or caching-proxy.


7.  Mixed trust mode

   If a signaling mechanism is created which reliably indicates that
   some data be used in caching-proxy mode, where other data be
   retrieved in trusted-proxy mode, the user-agent MAY create two
   tunnels (one for each mode).  A mechanism to signal this is not
   included in this document.  A single tunnel MUST NOT be used, as it
   is impossible to both allow inspection and privacy simultaneously
   using mechanisms as proposed here.


8.  Rejected Alternatives






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         Do nothing -
         This assumes that port 443 won't be blocked, which is contrary
         to the assumptions in this document.

         100% trust of the proxy at all times -
         Hopefully it is obvious why this is bad.

         Signed policy per response -
         With this mechanism, the user-agent would expect a piece of
         signed metadata with each message from the content-provider.
         This has the disadvantage of being fairly chatty, but the worst
         part is the requirement to be shuttling around private-key
         material on the part of the content-provider.  This material
         should be held closely; anything requiring its constant use
         will likely undermine its secrecy.  It is also expensive to be
         signing things all the time...

         Signed policy per domain or origin [RFC6454] -
         With this mechanism, the user-agent would expect a piece of
         signed metadata with the first response to a request.  The one-
         domain-one-policy seems too restrictive for today's site
         compositions, and doesn't match HTTP's current caching
         semantics.


9.  Impact on other areas of the protocol

   If we assume that we'll see widespread 'Caching Proxy' deployment,
   and we assume that the proxies will multiplex multiple incoming
   streams over fewer outgoing connections, then we may lose some of the
   current benefits of header compression, and must worry about endpoint
   per-connection stream limits.

   If the mechanisms in this document are widely used, mechanisms which
   reduce the number of RTTs for the TLS handshake phase(s) including
   anything which allows for fast, efficient, safe resumption would be
   of high importance.


10.  Security Considerations

   Everything in this document should be carefully scrutinized as
   everything in this document impacts security.

   A particular worry is the 'Trusted Proxy' mode.  Does its presence
   undermine end-to-end security so much that the benefit of the
   proposal is moot?  In particular, would users as a whole or in a
   significant part of the population be inclined to ignore (hopefully



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   dire) warnings about using 'Trusted Proxy' mode when they didn't own
   the proxy?


11.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


12.  Acknowledgements

   [RFC6454];


13.  Normative References

   [BITTORRENT]
              Cohen, B., "The BitTorrent Protocol Specification",
              BITTORRENT 11031, February 2008,
              <http://www.bittorrent.org/beps/bep_0003.html>.

   [DANE]     Hoffman, P. and J. Schlyter, "DANE", April 2012,
              <http://tools.ietf.org/html/draft-ietf-dane-protocol.txt>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2854]  Connolly, D. and L. Masinter, "The 'text/html' Media
              Type", RFC 2854, June 2000.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

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

   [RFC6249]  Bryan, A., McNab, N., Tsujikawa, T., Poeml, P., and H.
              Nordstrom, "Metalink/HTTP: Mirrors and Hashes", RFC 6249,
              June 2011.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,



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              December 2011.

   [SPDY]     Belshe, M. and R. Peon, "SPDY PROTOCOL",
              <http://tools.ietf.org/html/draft-mbelshe-httpbis-spdy>.


Author's Address

   Roberto Peon
   Google, Inc

   Email: fenix@google.com







































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