Transport Layer Security (TLS) Application Layer Protocol Negotiation Extension
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Network Working Group S. Friedl
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track A. Popov
Expires: August 1, 2013 Microsoft Corp.
January 28, 2013
Transport Layer Security (TLS) Application Layer Protocol Negotiation
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.
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Table of Contents
1.1. Requirements Language
1.2. Application Layer Protocol Negotiation Extension
1.3. Protocol Selection
1.4. Design Considerations
1.5. Security Considerations
1.6. IANA Considerations
3.1. Normative References
3.2. Informative References
Currently, the Next Protocol Negotiation extension (NPN) is used to
establish a SPDY [spdy] protocol session within a TLS RFC 5246
[RFC5246] session on port 443. NPN is not specific to SPDY and can
be used to negotiate sessions for a wide variety of protocols within
the TLS handshake.
NPN seeks to provide a reliable mechanism for application developers
to establish secure sessions for arbitrary protocols without
interference from firewalls, HTTP proxies and MITM proxies. It
addresses this goal by introducing a protocol negotiation process
into the TLS handshake under the constraints that no additional
roundtrips be added to the handshake and that the final protocol
selection be opaque to the network carrying the TLS session. Within
the NPN extension, it is the server that first generates and
transmits an offer of supported protocols to the client. The offer
is sent as part of the TLS ServerHello message before the
[ChangeCipherSpec] subprotocol has been started, therefore the list
of protocols supported by the server is transmitted in plaintext.
The client chooses a protocol which may or may not appear in the
offer from the server and then responds with the definitive protocol
selection answer. The client response is sent after the
[ChangeCipherSpec] subprotocol has been initiated, so the protocol
selected is encrypted in the client response.
In many other application layer protocol negotiation processes, it is
the client that first sends an offer of protocols it supports to the
server. The server then selects the protocol to be used in the
session and includes this answer in the response. RFC 3264 [RFC3264]
describes a SDP based offer/answer model which is not proscriptive in
terms of which party generates the offer, however in practice it is
typically the client generating the offer and the server replying
with the answer. This permits the server to act as the definitive
entity for selection of the application layer protocol.
This draft proposes an alternative formulation of the NPN protocol
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