wdiff rfc7301.original rfc7301.txt

Network Working Group
Internet Engineering Task Force (IETF) S. Friedl
Internet-Draft
Request for Comments: 7301 Cisco Systems, Inc.
Intended status:
Category: Standards Track A. Popov
Expires: September 4, 2014
ISSN: 2070-1721 Microsoft Corp.
A. Langley
Google Inc.
E. Stephan
Orange
March 3,
July 2014

Transport Layer Security (TLS) Application Layer
Application-Layer Protocol Negotiation Extension
draft-ietf-tls-applayerprotoneg-05

Abstract

This document describes a Transport Layer Security (TLS) extension
for application layer application-layer protocol negotiation within the TLS handshake.
For instances in which multiple application protocols are supported
on the TLS connection is established over a well
known same TCP or UDP port not associated with the desired application
layer protocol, port, this extension allows the application
layer to negotiate which protocol will be used within the TLS
connection.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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Internet-Drafts are draft documents valid the IETF community. It has
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Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

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This Internet-Draft will expire on September 4, 2014.
http://www.rfc-editor.org/info/rfc7301.

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Table of Contents

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

1. Introduction

Increasingly, application layer 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 that 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])
HTTP/2 ([HTTP2]) over TLS, however TLS; however, ALPN facilitates negotiation of
arbitrary application layer application-layer protocols.

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 Application-Layer Protocol Negotiation

3.1. The Application Layer 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,
IANA-registered, opaque, non-empty byte strings, as described further
in Section 6 "IANA Considerations" ("IANA Considerations") of this document. Empty strings
MUST NOT be included and byte strings MUST NOT be truncated . truncated.

Servers that receive a client hello ClientHello containing the
"application_layer_protocol_negotiation" extension, 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
is 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
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

* Indicates optional or situation-dependent messages that are not
always sent.

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
[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 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 that it supports which and that 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 protocol identified in the
"application_layer_protocol_negotiation" extension type in the
ServerHello SHALL be definitive for the connection, until
renegotiated. 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
the established TLS architecture. The
"application_layer_protocol_negotiation" ServerHello extension is
intended to be definitive for the connection (until the connection is
renegotiated) and is sent in plaintext to permit network elements to
provide differentiated service for the connection when the TCP or UDP
port number is not definitive for the application layer 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 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.

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 application-layer protocol
associated with the TLS connection. Historically, the application application-
layer protocol associated with a connection could be ascertained from
the TCP or UDP port number in use.

Implementers and document editors who intend to extend the protocol
identifier registry by adding new protocol identifiers should
consider that in TLS versions 1.2 and below the client sends these
identifiers in the clear, and clear. They should also consider that that, for at
least the next decade, it is expected that browsers would normally
use these earlier versions of TLS in the initial ClientHello.

Care must be taken when such identifiers may leak personally
identifiable information, or when such leakage may lead to profiling, profiling
or to leaking of sensitive information. If any of these apply to
this new protocol identifier, the identifier SHOULD NOT be used in
TLS configurations where it would be visible in the clear, and
documents specifying such protocol identifiers SHOULD recommend
against such unsafe use.

6. IANA Considerations

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

16 application_layer_protocol_negotiation

This document establishes a registry for protocol identifiers
entitled "Application Layer "Application-Layer Protocol Negotiation (ALPN) Protocol IDs"
under the existing "Transport Layer Security (TLS)" (TLS) Extensions"
heading.

Entries in this registry require the following fields:

o Protocol: The name of the protocol.
o Identification Sequence: The precise set of octet values that
identifies the protocol. This could be the UTF-8 encoding
[RFC3629] of the protocol name.
o Specification: Reference: A reference to a specification that defines the
protocol.

This registry operates under the "Expert Review" policy as defined in
[RFC5226]. The designated expert is advised to encourage the
inclusion of a reference to a permanent and readily available
specification that enables the creation of interoperable
implementations of the identified protocol.

The initial set of registrations for this registry is as follows:

Protocol: HTTP/1.1
Identification Sequence:
0x68 0x74 0x74 0x70 0x2f 0x31 0x2e 0x31 ("http/1.1")

Specification: http://tools.ietf.org/html/rfc2616
Reference: [RFC7230]

Protocol: SPDY/1
Identification Sequence:
0x73 0x70 0x64 0x79 0x2f 0x31 ("spdy/1")

Specification: http://dev.chromium.org/spdy/spdy-protocol/spdy-
protocol-draft1
Reference:
http://dev.chromium.org/spdy/spdy-protocol/spdy-protocol-draft1

Protocol: SPDY/2
Identification Sequence:
0x73 0x70 0x64 0x79 0x2f 0x32 ("spdy/2")

Specification: http://dev.chromium.org/spdy/spdy-protocol/spdy-
protocol-draft2
Reference:
http://dev.chromium.org/spdy/spdy-protocol/spdy-protocol-draft2
Protocol: SPDY/3
Identification Sequence:
0x73 0x70 0x64 0x79 0x2f 0x33 ("spdy/3")

Specification: http://dev.chromium.org/spdy/spdy-protocol/spdy-
protocol-draft3
Reference:
http://dev.chromium.org/spdy/spdy-protocol/spdy-protocol-draft3

7. Acknowledgements

This document benefitted specifically from the NPN Next Protocol
Negotiation (NPN) extension draft document authored by Adam Langley and
from discussions with Tom Wesselman and Cullen Jennings 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.

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

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

[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.

8.2. Informative References

[I-D.ietf-httpbis-http2]

[HTTP2] Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
Protocol version 2", draft-ietf-httpbis-http2-10 (work Work in
progress), February Progress, June 2014.

[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

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

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

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

Email:

EMail: andreipo@microsoft.com

Adam Langley
Google Inc.
USA

Email:

EMail: agl@google.com

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

Email:

EMail: emile.stephan@orange.com