Internet DRAFT - draft-ietf-httpbis-tunnel-protocol
draft-ietf-httpbis-tunnel-protocol
HTTP Working Group A. Hutton
Internet-Draft Unify
Intended status: Standards Track J. Uberti
Expires: December 13, 2015 Google
M. Thomson
Mozilla
June 11, 2015
The ALPN HTTP Header Field
draft-ietf-httpbis-tunnel-protocol-05
Abstract
This specification allows HTTP CONNECT requests to indicate what
protocol is intended to be used within the tunnel once established,
using the ALPN header field.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 13, 2015.
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. The ALPN HTTP Header Field . . . . . . . . . . . . . . . . . 3
2.1. Header Field Values . . . . . . . . . . . . . . . . . . . 3
2.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . 6
5.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The HTTP CONNECT method (Section 4.3.6 of [RFC7231]) requests that
the recipient establish a tunnel to the identified origin server and
thereafter forward packets, in both directions, until the tunnel is
closed. Such tunnels are commonly used to create end-to-end virtual
connections, through one or more proxies.
The HTTP ALPN header field identifies the protocol or protocols that
the client intends to use within a tunnel that is established using
CONNECT. This uses the Application Layer Protocol Negotiation
identifier (ALPN, [RFC7301]).
For a tunnel that is then secured using TLS [RFC5246], the header
field carries the same application protocol label as will be carried
within the TLS handshake [RFC7301]. If there are multiple possible
application protocols, all of those application protocols are
indicated.
The ALPN header field carries an indication of client intent only.
An ALPN identifier is used here only to identify the application
protocol or suite of protocols that the client intends to use in the
tunnel. No negotiation takes place using this header field. In TLS,
the final choice of application protocol is made by the server from
the set of choices presented by the client. Other substrates could
negotiate the application protocol differently.
Proxies do not implement the tunneled protocol, though they might
choose to make policy decisions based on the value of the header
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field. For example, a proxy could use the application protocol to
select appropriate traffic prioritization.
1.1. 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 RFC 2119 [RFC2119].
2. The ALPN HTTP Header Field
Clients include the ALPN header field in an HTTP CONNECT request to
indicate the application layer protocol that a client intends to use
within the tunnel, or a set of protocols that might be used within
the tunnel.
2.1. Header Field Values
Valid values for the protocol field are taken from the "Application-
Layer Protocol Negotiation (ALPN) Protocol ID" registry ([1])
established by [RFC7301].
2.2. Syntax
The ABNF (Augmented Backus-Naur Form) syntax for the ALPN header
field value is given below. It uses the syntax defined in
Section 1.2 of [RFC7230].
ALPN = 1#protocol-id
protocol-id = token ; percent-encoded ALPN protocol identifier
ALPN protocol names are octet sequences with no additional
constraints on format. Octets not allowed in tokens ([RFC7230],
Section 3.2.6) MUST be percent-encoded as per Section 2.1 of
[RFC3986]. Consequently, the octet representing the percent
character "%" (hex 25) MUST be percent-encoded as well.
In order to have precisely one way to represent any ALPN protocol
name, the following additional constraints apply:
o Octets in the ALPN protocol MUST NOT be percent-encoded if they
are valid token characters except "%", and
o When using percent-encoding, uppercase hex digits MUST be used.
With these constraints, recipients can apply simple string comparison
to match protocol identifiers.
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For example:
CONNECT www.example.com HTTP/1.1
Host: www.example.com
ALPN: h2, http%2F1.1
2.3. Usage
When used in the ALPN header field, an ALPN identifier is used to
identify an entire application protocol stack, not a single protocol
layer or component.
For a CONNECT tunnel that conveys a protocol secured with TLS, the
value of the ALPN header field contains the same list of ALPN
identifiers that will be sent in the TLS ClientHello message
[RFC7301].
Where no protocol negotiation is expected to occur, such as in
protocols that do not use TLS, the ALPN header field contains a
single ALPN Protocol Identifier corresponding to the application
protocol that is intended to be used. If an alternative form of
protocol negotiation is possible, the ALPN header field contains the
set of protocols that might be negotiated.
A proxy can use the value of the ALPN header field to more cleanly
and efficiently reject requests for a CONNECT tunnel. Exposing
protocol information at the HTTP layer allows a proxy to deny
requests earlier, with better error reporting (such as a 403 status
code). The ALPN header field can be falsified and is therefore not
sufficient basis for authorizing a request.
A proxy could attempt to inspect packets to determine the protocol in
use. This requires that the proxy understand each ALPN identifier.
Protocols like TLS could hide negotiated protocols, or protocol
negotiation details could change over time. Proxies SHOULD NOT break
a CONNECT tunnel solely on the basis of a failure to recognize the
protocol.
A proxy can use the ALPN header field value to change how it manages
or prioritizes connections.
3. IANA Considerations
HTTP header fields are registered within the "Permanent Message
Header Field Names" registry maintained at [2]. This document
defines and registers the ALPN header field, according to [RFC3864]
as follows:
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Header Field Name: ALPN
Protocol: http
Status: Standard
Reference: Section 2
Change Controller: IETF (iesg@ietf.org) - Internet Engineering Task
Force
4. Security Considerations
In case of using HTTP CONNECT to a TURN server ("Traversal Using
Relays around NAT", [RFC5766]) the security considerations of
Section 4.3.6 of [RFC7231] apply. It states that there "are
significant risks in establishing a tunnel to arbitrary servers,
particularly when the destination is a well-known or reserved TCP
port that is not intended for Web traffic. Proxies that support
CONNECT SHOULD restrict its use to a limited set of known ports or a
configurable whitelist of safe request targets."
The ALPN header field described in this document is OPTIONAL.
Clients and HTTP proxies could choose to not support it and therefore
either fail to provide it, or ignore it when present. If the header
field is not available or ignored, a proxy cannot identify the
purpose of the tunnel and use this as input to any authorization
decision regarding the tunnel. This is indistinguishable from the
case where either client or proxy does not support the ALPN header
field.
There is no confidentiality protection for the ALPN header field.
ALPN identifiers that might expose confidential or sensitive
information SHOULD NOT be sent, as described in Section 5 of
[RFC7301].
The value of the ALPN header field could be falsified by a client.
If the data being sent through the tunnel is encrypted (for example,
with TLS [RFC5246]), then the proxy might not be able to directly
inspect the data to verify that the claimed protocol is the one which
is actually being used, though a proxy might be able to perform
traffic analysis [TRAFFIC]. A proxy therefore cannot rely on the
value of the ALPN header field as a policy input in all cases.
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5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004,
<http://www.rfc-editor.org/info/rfc3864>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI
10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Semantics and Content", RFC 7231, DOI
10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <http://www.rfc-editor.org/info/rfc7301>.
5.2. Informative References
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766, DOI
10.17487/RFC5766, April 2010,
<http://www.rfc-editor.org/info/rfc5766>.
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[TRAFFIC] Pironti, A., Strub, P-Y., and K. Bhargavan, "Website Users
by TLS Traffic Analysis: New Attacks and Effective
Countermeasures, Revision 1", 2012,
<https://alfredo.pironti.eu/research/publications/full/
identifying-website-users-tls-traffic-analysis-new-
attacks-and-effective-counterme>.
5.3. URIs
[1] http://www.iana.org/assignments/tls-extensiontype-values/#alpn-
protocol-ids
[2] https://www.iana.org/assignments/message-headers
Authors' Addresses
Andrew Hutton
Unify
Technology Drive
Nottingham NG9 1LA
UK
EMail: andrew.hutton@unify.com
Justin Uberti
Google
747 6th Ave S
Kirkland, WA 98033
US
EMail: justin@uberti.name
Martin Thomson
Mozilla
331 E Evelyn Street
Mountain View, CA 94041
US
EMail: martin.thomson@gmail.com
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