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Versions: (draft-friedl-tls-applayerprotoneg) 00 01 02 03 04 05

Network Working Group                                        S.F. Friedl
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                                A. Popov
Expires: October 27, 2013                                Microsoft Corp.
                                                              A. Langley
                                                             Google Inc.
                                                              E. Stephan
                                                 France Telecom - Orange
                                                          April 25, 2013


 Transport Layer Security (TLS) Application Layer Protocol Negotiation
                               Extension
                   draft-ietf-tls-applayerprotoneg-01

Abstract

   This document describes a Transport Layer Security (TLS) extension
   for application layer protocol negotiation within the TLS handshake.
   For instances in which the TLS connection is established over a well
   known TCP/IP port not associated with the desired application layer
   protocol, this extension allows the application layer to negotiate
   which protocol will be used within the TLS session.

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 October 27, 2013.

Copyright Notice

   Copyright (c) 2013 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



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   (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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Application Layer Protocol Negotiation  . . . . . . . . . . .   3
     3.1.  The Application Layer Protocol Negotiation Extension  . .   3
     3.2.  Protocol Selection  . . . . . . . . . . . . . . . . . . .   5
   4.  Design Considerations . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Increasingly, application layer protocols are encapsulated in the TLS
   security protocol [RFC5246].  This encapsulation enables applications
   to use the existing, secure communications links already present on
   port 443 across virtually the entire global IP infrastructure.

   When multiple application protocols are supported on a single server-
   side port number, such as port 443, the client and the server need to
   negotiate an application protocol for use with each connection.  It
   is desirable to accomplish this negotiation without adding network
   round-trips between the client and the server, as each round-trip
   will degrade an end-user's experience.  Further, it would be
   advantageous to allow certificate selection based on the negotiated
   application protocol.

   This document specifies a TLS extension which permits the application
   layer to negotiate protocol selection within the TLS handshake.  This
   work was requested by the HTTPbis WG to address the negotiation of
   HTTP version ([RFC2616], [I-D.ietf-httpbis-http2]) over TLS, however
   ALPN facilitates negotiation of arbitrary application layer
   protocols.





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   With ALPN, the client sends the list of supported application
   protocols as part of the TLS ClientHello message.  The server chooses
   a protocol and sends the selected protocol as part of the TLS
   ServerHello message.  The application protocol negotiation can thus
   be accomplished within the TLS handshake, without adding network
   round-trips, and allows the server to associate a different
   certificate with each application protocol, if desired.

2.  Requirements Language

   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].

3.  Application Layer Protocol Negotiation

3.1.  The Application Layer Protocol Negotiation Extension

   A new extension type ("application_layer_protocol_negotiation(16)")
   is defined and MAY be included by the client in its "ClientHello"
   message.

   enum {
       application_layer_protocol_negotiation(16), (65535)
   } ExtensionType;


   The "extension_data" field of the
   ("application_layer_protocol_negotiation(16)") extension SHALL
   contain a "ProtocolNameList" value.

   opaque ProtocolName<1..2^8-1>;

   struct {
       ProtocolName protocol_name_list<2..2^16-1>
   } ProtocolNameList;


   "ProtocolNameList" contains the list of protocols advertised by the
   client, in descending order of preference.  Protocols are named by
   IANA registered, opaque, non-empty byte strings, as described further
   in Section 6 "IANA Considerations" of this document.  Implementations
   MUST ensure that an empty string is not included and that no byte
   strings are truncated.

   Experimental protocol names, which are not registered by IANA, will
   start with the following sequence of bytes: 0x65, 0x78, 0x70 ("exp").




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   Servers that receive a client hello containing the
   "application_layer_protocol_negotiation" extension, MAY return a
   suitable protocol selection response to the client.  The server will
   ignore any protocol name that it does not recognize.  A new
   ServerHello extension type
   ("application_layer_protocol_negotiation(16)") MAY be returned to the
   client within the extended ServerHello message.  The "extension_data"
   field of the ("application_layer_protocol_negotiation(16)") extension
   SHALL be structured the same as described above for the client
   "extension_data", except that the "ProtocolNameList" MUST contain
   exactly one "ProtocolName".

   Therefore, a full handshake with the
   "application_layer_protocol_negotiation" extension in the ClientHello
   and ServerHello messages has the following flow (contrast with
   section 7.3 of [RFC5246]):

   Client                                              Server

   ClientHello                     -------->       ServerHello
     (ALPN extension &                               (ALPN extension &
      list of protocols)                              selected protocol)
                                                   Certificate*
                                                   ServerKeyExchange*
                                                   CertificateRequest*
                                   <--------       ServerHelloDone
   Certificate*
   ClientKeyExchange
   CertificateVerify*
   [ChangeCipherSpec]
   Finished                        -------->
                                                   [ChangeCipherSpec]
                                   <--------       Finished
   Application Data                <------->       Application Data

                                 Figure 1

   An abbreviated handshake with the
   "application_layer_protocol_negotiation" extension has the following
   flow:

   Client                                              Server

   ClientHello                     -------->       ServerHello
     (ALPN extension &                               (ALPN extension &
      list of protocols)                              selected protocol)
                                                   [ChangeCipherSpec]
                                   <--------       Finished



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   [ChangeCipherSpec]
   Finished                        -------->
   Application Data                <------->       Application Data

                                 Figure 2

   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.

3.2.  Protocol Selection

   It is expected that a server will have a list of protocols that it
   supports, in preference order, and will only select a protocol if the
   client supports it.  In that case, the server SHOULD select the most
   highly preferred protocol it supports which is also advertised by the
   client.  In the event that the server supports no protocols that the
   client advertises, then the server SHALL respond with a fatal
   "no_application_protocol" alert.

   enum {
       no_application_protocol(120),
       (255)
   } AlertDescription;


   The "no_application_protocol" fatal alert is only defined for the
   "application_layer_protocol_negotiation" extension and MUST NOT be
   sent unless the server has received a ClientHello message containing
   this extension.

   The protocol identified in the
   "application_layer_protocol_negotiation" extension type in the
   ServerHello SHALL be definitive for the connection.  The server SHALL
   NOT respond with a selected protocol and subsequently use a different
   protocol for application data exchange.

4.  Design Considerations

   The ALPN extension is intended to follow the typical design of TLS
   protocol extensions.  Specifically, the negotiation is performed
   entirely within the client/server hello exchange in accordance with
   established TLS architecture.  The
   "application_layer_protocol_negotiation" ServerHello extension is
   intended to be definitive for the connection and is sent in plaintext
   to permit network elements to provide differentiated service for the



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   connection when the TCP/IP port number is not definitive for the
   application layer protocol to be used in the connection.  By placing
   ownership of protocol selection on the server, ALPN facilitates
   scenarios in which certificate selection or connection rerouting may
   be based on the negotiated protocol.

   Finally, by managing protocol selection in the clear as part of the
   handshake, ALPN avoids introducing false confidence with respect to
   the the ability to hide the negotiated protocol in advance of
   establishing the connection.  If hiding the protocol is required,
   then renegotiation after connection establishment, which would
   provide true TLS security guarantees, would be a preferred
   methodology.

   A namespace will be assigned for experimental protocols, comprising
   byte strings which start with the following sequence of bytes: 0x65,
   0x78, 0x70 ("exp").  Assignments in this namespace do not need IANA
   registration.

5.  Security Considerations

   The ALPN extension does not impact the security of TLS session
   establishment or application data exchange.  ALPN serves to provide
   an externally visible marker for the application layer protocol
   associated with the TLS connection.  Historically, the application
   layer protocol associated with a connection could be ascertained from
   the TCP/IP port number in use.

6.  IANA Considerations

   The IANA has updated its Registry of TLS ExtensionType Values to
   include the following entry:

   - 16 application_layer_protocol_negotiation

   This document also requires the IANA to create a registry of
   Application Layer Protocol Negotiation protocol byte strings,
   initially containing the following entries:

   - "http/1.1": HTTP/1.1 [RFC2616];

   - "http/2.0": HTTP/2.0 [I-D.ietf-httpbis-http2];

   - "spdy/1": (obsolete) SPDY version 1;

   - "spdy/2": SPDY version 2;

   - "spdy/3": SPDY version 3.



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   We propose that this new registry be created in a new page entitled:
   "Application Layer Protocol Negotiation (ALPN) Protocol IDs" beneath
   the existing heading of "Transport Layer Security (TLS)".

7.  Acknowledgements

   This document benefitted specifically from the NPN extension draft
   authored by Adam Langley and from discussions with Tom Wesselman and
   Cullen Jennings both of Cisco.

8.  References

8.1.  Normative References

   [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.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264, June
              2002.

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

   [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
              Extension Definitions", RFC 6066, January 2011.

8.2.  Informative References

   [I-D.ietf-httpbis-http2]
              Belshe, M., Peon, R., Thomson, M., and A. Melnikov,
              "Hypertext Transfer Protocol version 2.0", draft-ietf-
              httpbis-http2-02 (work in progress), April 2013.

   [I-D.mbelshe-httpbis-spdy]
              Belshe, M. and R. Peon, "SPDY Protocol", draft-mbelshe-
              httpbis-spdy-00 (work in progress), February 2012.

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

Authors' Addresses




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   Stephan Friedl
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Phone: (720)562-6785
   Email: sfriedl@cisco.com


   Andrei Popov
   Microsoft Corp.
   One Microsoft Way
   Redmond, WA  98052
   USA

   Email: andreipo@microsoft.com


   Adam Langley
   Google Inc.
   USA

   Email: agl@google.com


   Emile Stephan
   France Telecom - Orange
   2 avenue Pierre Marzin
   Lannion  F-22307
   France

   Email: emile.stephan@orange.com

















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