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Network Working Group                                         A. Langley
Internet-Draft                                                Google Inc
Intended status: Standards Track                        January 20, 2010
Expires: July 24, 2010


   Transport Layer Security (TLS) Next Protocol Negotiation Extension
                     draft-agl-tls-nextprotoneg-00

Abstract

   This document describes a Transport Layer Security (TLS) extension
   for application layer protocol negotiation.  This allows the
   application layer to negotiate which protocol should be performed
   over the secure connection in a manner which avoids additional round
   trips and which is independent of the application layer protocols.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on July 24, 2010.

Copyright Notice

   Copyright (c) 2010 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



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   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 BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
   3.  Next Protocol Negotiation Extension  . . . . . . . . . . . . .  5
   4.  Security considerations  . . . . . . . . . . . . . . . . . . .  6
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     7.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Changes . . . . . . . . . . . . . . . . . . . . . . . 10
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11






























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1.  Introduction

   The use of TLS [RFC5246] over TCP [RFC0793] unavoidably adds at least
   a round trip to the time taken to establish a connection.  By
   allowing the application layer to perform negotiation during that
   round trip one gains several advantages:

   Firstly, for various reasons, different application layer protocols
   are increasingly being carried over TLS using a small set of TCP port
   numbers, most often port 443.  Rather than forcing systems
   administrators to use different IP addresses for every service,
   negotiation allows multiple services to exist with the same IP
   address.

   Secondly, newer versions of the same application layer protocol can
   perform discovery and avoid additional round trips after the TLS
   handshake.

   To illustrate the second point, consider HTTP [RFC2616] pipelining.
   Although it has seen little adoption because of interference from
   middleware, there is no reason not to use it over TLS where the
   transport is known to be pristine.

   However, even over TLS, the client cannot make pipelined requests
   until the first reply indicates that the remote peer supports the
   feature.  If the client could negotiate HTTP/1.1 support before the
   first request, it could start sending pipelined requests immediately.
























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2.  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 RFC 2119 [RFC2119].














































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3.  Next Protocol Negotiation Extension

   A new extension type ("next_protocol_negotiation(TBD)") is defined
   and MAY be included by the client in its "ClientHello" message.  If,
   and only if, the server sees this extension in the "ClientHello", it
   MAY choose to include the extension in its "ServerHello".

   enum {
     next_protocol_negotiation(TBD), (65535)
   } ExtensionType;

   A new handshake message type ("next_protocol(TBD)") is defined.  If,
   and only if, the server included a "next_protocol_negotiation"
   extension in its ServerHello message, the client MUST send a
   "NextProtocol" message after its "ChangeCipherSpec" and before its
   "Finished" message.

   struct {
     opaque selected_protocol<0..255>;
     opaque padding<0..255>;
   } NextProtocol;

   The "extension_data" field of a "next_protocol_negotiation" in a
   "ClientHello" MUST be empty.

   The "extension_data" field in a "ServerHello" and the "NextProtocol"
   message contain opaque bytes to be used by the application layer to
   negotiate the application layer protocol.  The format of this data is
   not specified in this draft.

   Unlike many other TLS extensions, this extension does not establish
   properties of the session, only of the connection.  When session
   resumption or session tickets [RFC5077] are used, the previous
   contents of this extension are irrelevant and only the values in the
   new handshake messages are considered.

   For the same reasons, after a handshake has been performed for a
   given connection, renegotiations on the same connection MUST NOT
   include the "next_protocol_negotiation" extension.












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4.  Security considerations

   The server's list of supported protocols is still advertised in the
   clear with this extension.  This may be undesirable for certain
   protocols (such as Tor [tor]) where one could imagine that hostile
   networks would terminate any TLS connection with a server that
   advertised such a capability.  In this case, clients may wish to
   opportunistically select a protocol that wasn't advertised by the
   server.  However, the workings of such a scheme are outside the scope
   of this document.









































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5.  IANA Considerations

   This document requires IANA to update its registry of TLS extensions
   to assign an entry, referred herein as "next_protocol_negotiation".

   This document also requires IANA to update its registry of TLS
   handshake types to assign an entry, referred herein as
   "next_protocol".











































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6.  Acknowledgements

   This document benefited specifically from discussions with Wan-Teh
   Chang and Nagendra Modadugu.















































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7.  References

7.1.  Normative References

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

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

7.2.  Informative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [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.

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, January 2008.

   [tor]      Dingledine, R., Matthewson, N., and P. Syverson, "Tor: The
              Second-Generation Onion Router", August 2004.


























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Appendix A.  Changes

   To be removed by RFC Editor before publication
















































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Author's Address

   Adam Langley
   Google Inc

   Email: agl@google.com













































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