websec A. Barth
Internet-Draft Google, Inc.
Intended status: Standards Track October 7, 2010
Expires: April 10, 2011
The Web Origin Concept
draft-abarth-origin-08
Abstract
This document defines the concept of an "origin", which represents a
web pincipal. Typically, user agents isolate content retrieved from
different origins to prevent a malicious web site operator for
interfering with the operation of benign web sites. In particular,
this document defines how to compute an origin from a URI, how to
serialize an origin to a string, and an HTTP header, named "Origin",
for indicating which origin caused the user agent to issue a
particular request.
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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 10, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
Barth Expires April 10, 2011 [Page 1]
Internet-Draft The Web Origin Concept October 2010
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
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. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Conformance Criteria . . . . . . . . . . . . . . . . . . . 4
2.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 4
2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Comparing Origins . . . . . . . . . . . . . . . . . . . . . . 8
5. Serializing Origins . . . . . . . . . . . . . . . . . . . . . 9
5.1. Unicode Serialization of an Origin . . . . . . . . . . . . 9
5.2. ASCII Serialization of an Origin . . . . . . . . . . . . . 9
6. The HTTP Origin header . . . . . . . . . . . . . . . . . . . . 11
6.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 11
6.3. User Agent Requirements . . . . . . . . . . . . . . . . . 11
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
10. Implementation Considerations . . . . . . . . . . . . . . . . 16
10.1. IDNA dependency and migration . . . . . . . . . . . . . . 16
11. Normative References . . . . . . . . . . . . . . . . . . . . . 17
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19
Barth Expires April 10, 2011 [Page 2]
Internet-Draft The Web Origin Concept October 2010
1. Introduction
[TODO: Introduction.]
Barth Expires April 10, 2011 [Page 3]
Internet-Draft The Web Origin Concept October 2010
2. Conventions
2.1. Conformance Criteria
The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in [RFC2119].
Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and abort these
steps") are to be interpreted with the meaning of the key word
("MUST", "SHOULD", "MAY", etc) used in introducing the algorithm.
Conformance requirements phrased as algorithms or specific steps can
be implemented in any manner, so long as the end result is
equivalent. In particular, the algorithms defined in this
specification are intended to be easy to understand and are not
intended to be performant.
2.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234].
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
sequence of data), SP (space), HTAB (horizontal tab), CHAR (any US-
ASCII character), VCHAR (any visible US-ASCII character), and WSP
(whitespace).
The OWS (optional whitespace) rule is used where zero or more linear
whitespace characters MAY appear:
OWS = *( [ obs-fold ] WSP )
; "optional" whitespace
obs-fold = CRLF
OWS SHOULD either not be produced or be produced as a single SP
character.
2.3. Terminology
The terms user agent, client, server, proxy, and origin server have
the same meaning as in the HTTP/1.1 specification ([RFC2616], Section
1.3).
Barth Expires April 10, 2011 [Page 4]
Internet-Draft The Web Origin Concept October 2010
A globally unique identifier is a value which is different from all
other previously existing values. For example, a sufficiently long
random string is likely to be a globally unique indentifier.
A idna-canonicalization host name is the string generated by the
following algorithm:
1. Convert the host name to a sequence of NR-LDH labels (see Section
2.3.2.2 of [RFC5890]) and/or A-labels according to the
appropriate IDNA specification [RFC5891] or [RFC3490] (see
Section 10.1 of this specification)
2. Convert the labels to lower case.
3. Concatenate the labels, separating each label from the next with
a %x2E (".") character.
Barth Expires April 10, 2011 [Page 5]
Internet-Draft The Web Origin Concept October 2010
3. Origin
An origin represents a web principal. Typically, user agents
determine the origin of a piece of content from the URI from which
they retrieved the URI. In this section, we define how to compute an
origin from a URI.
The origin of a URI is the value computed by the following algorithm:
1. If the URI does not use a server-based naming authority, or if
the URI is not an absolute URI, then return a globally unqiue
identifier.
2. Let scheme be the scheme component of the URI, converted to
lowercase.
3. If the implementation doesn't support the protocol given by
scheme, then return a globally unique identifier.
4. If scheme is "file", the implementation MAY return an
implementation-defined value.
1. NOTE: Historically, user agents have granted the file a
tremendous amout of authority. However, granting all local
files such wide privileges can lead to privilege escalation
attacks. Some user agents have had success grant local files
directory-based privileges, but this approach has not been
widely adopted. Other user agent use a globally unique
identifier for file URLs, which is the most secure option.
5. Let host be the idna-canonicalization of the host component of
the URI.
6. If there is no port component of the URI:
1. Let port be the default port for the protocol given by
scheme.
Otherwise:
2. Let port be the port component of the URI.
7. Return the tuple (scheme, host, port).
Implementations MAY define other types of origins in addition to the
scheme/host/port tuple type defined above. For example, an
implementation might define an origin based on a public key or an
implementation might append addition "sandbox" bits to a scheme/host/
Barth Expires April 10, 2011 [Page 6]
Internet-Draft The Web Origin Concept October 2010
port tuple.
Barth Expires April 10, 2011 [Page 7]
Internet-Draft The Web Origin Concept October 2010
4. Comparing Origins
To origins are "the same" if, and only if, they are identicial. In
particular:
o If the two origins are scheme/host/port tuples, the two origins
are the same if, and only if, they have identical schemes, hosts,
and ports.
o An origin that is globally unique identifier cannot be the same as
an origin that is a scheme/host/port tuple.
o Two origins that are globally unique identifiers cannot be the
same if they were created at different times, even if they were
created for the same URI.
Two URIs are the same-origin if their origins are the same.
NOTE: It is possible for a URIs to not be same-origin with itself.
For example, a data URIs is not same-origin with itself because
data URIs do not use a server-based naming authority and hence
have globally unique identifiers as origins.
Barth Expires April 10, 2011 [Page 8]
Internet-Draft The Web Origin Concept October 2010
5. Serializing Origins
This section defines how to serialize an origin to a unicode string
and to an ASCII string.
5.1. Unicode Serialization of an Origin
The unicode-serialization of an origin is the value returned by the
following algorithm:
1. If the origin is not a scheme/host/port tuple, then return the
string
null
(i.e., the code point sequence U+006E, U+0075, U+006C, U+006C)
and abort these steps.
2. Otherwise, let result be the scheme part of the origin tuple.
3. Append the string "://" to result.
4. Append the [TODO: IDNA ToUnicode] algorithm to each component of
the host part of the origin tuple, and append the results of each
component, in the same order, separated by U+002E FULL STOP code
points (".") to result.
5. If the port part of the origin tuple is different than the
default port for the protocol given by the scheme part of the
origin tuple:
1. Append a U+003A COLON code points (":") and the given port,
in base ten, to result.
6. Return result.
[TODO: Check that we handle IPv6 literals correctly.]
5.2. ASCII Serialization of an Origin
The ascii-serialization of an origin is the value returned by the
following algorithm:
1. If the origin is not a scheme/host/port tuple, then return the
string
null
Barth Expires April 10, 2011 [Page 9]
Internet-Draft The Web Origin Concept October 2010
(i.e., the code point sequence U+006E, U+0075, U+006C, U+006C)
and abort these steps.
2. Otherwise, let result be the scheme part of the origin tuple.
3. Append the string "://" to result.
4. Append the host port of the origin tuple to result.
5. If the port part of the origin tuple is different than the
default port for the protocol given by the scheme part of the
origin tuple:
1. Append a U+003A COLON code points (":") and the given port,
in base ten, to result.
6. Return result.
Barth Expires April 10, 2011 [Page 10]
Internet-Draft The Web Origin Concept October 2010
6. The HTTP Origin header
This section defines the HTTP Origin header.
6.1. Syntax
The Origin header has the following syntax:
origin = "Origin:" OWS origin-list-or-null OWS
origin-list-or-null = "null" / origin-list
origin-list = serialized-origin *( SP serialized-origin )
serialized-origin = scheme "://" host [ ":" port ]
; <scheme>, <host>, <port> productions from RFC3986
6.2. Semantics
When included in an HTTP request, the Origin header indicates the
origin(s) that caused the user agent to generate the request.
For example, consider a user agent that executes scripts on behalf of
origins. If one of those scripts causes the user agent to issue an
HTTP request, the user agent might wish to inform the server that the
request was issued by the script using the Origin header.
In some cases, a number of origins contribute to causing the user
agents to issue an HTTP request. In those cases, user agent can list
all the origins in the Origin header. For example, if the HTTP
request was initially generated by one origin, but then later
redirected by another origin, the user agent might wish to inform the
server that two origins were invovled in causing the user agent to
generate the request.
6.3. User Agent Requirements
The user agent MAY include an Origin header in any HTTP request.
The user agent MUST NOT include more than one Origin header field in
any HTTP request.
Whenever a user agent issues an HTTP request from a "privacy-
sensitive" context, the user agent MUST send the value "null" in the
Origin header.
NOTE: This document does not define the notion of a privacy-
sensitive context. Applications that generate HTTP requests can
define contexts as privacy-sensitive to impose restrictions on how
Barth Expires April 10, 2011 [Page 11]
Internet-Draft The Web Origin Concept October 2010
user agents generate Origin headers.
When generating an Origin header, the user agent MUST meet the
following requirements:
o Each of the serialized-origin productions in the grammar MUST be
the ascii-serialization of an origin.
o No two consequitive serialized-origin productions in the grammar
can be identical. In particular, if the user agent would generate
two consequitive serialized-origins, the user agent MUST NOT
generate the second one.
If the user agent generated an HTTP request current-request because
the user agent received 3xx Status Code response to another HTTP
request previous-request for URI previous-uri:
o The HTTP request current-request MUST include an Origin header.
o The value of the Origin header MUST be either:
* The string "null" (i.e., the code point sequence U+006E,
U+0075, U+006C, U+006C).
* The value of the Origin header in the previous-request. The
user agent MUST NOT choose this option if the ascii-
serialization of previous-uri is not identical to the last
serialized-origin in the Origin header of the previous request.
* The value of the Origin header in previous header extended with
a space and the ascii-serialziation of the origin of previous-
uri. The user agent MUST NOT choose this option if the ascii-
serialziation of the origin of previous-uri is "null".
The user agent SHOULD include the Origin header in an HTTP request if
the user agent issues the HTTP request on behalf of a remote origin
(e.g., and by the user operating a trusted user interface surface).
In this case, the user agent should set the value of the Origin
header to the ascii-serialization of that origin.
NOTE: This behavior differs from the usual user agent behavior for
the HTTP Referer header, which user agents often suppress when an
origin with an "https" scheme issues a request for a URI with an
"http" scheme.
Barth Expires April 10, 2011 [Page 12]
Internet-Draft The Web Origin Concept October 2010
7. Privacy Considerations
[TODO: Privacy considerations.]
Barth Expires April 10, 2011 [Page 13]
Internet-Draft The Web Origin Concept October 2010
8. Security Considerations
[TODO: Security considerations.]
Barth Expires April 10, 2011 [Page 14]
Internet-Draft The Web Origin Concept October 2010
9. IANA Considerations
[TODO: Register the Origin header.]
Barth Expires April 10, 2011 [Page 15]
Internet-Draft The Web Origin Concept October 2010
10. Implementation Considerations
10.1. IDNA dependency and migration
IDNA2008 [RFC5890] supersedes IDNA2003 [RFC3490] but is not
backwards-compatible. For this reason, there will be a transition
period (possibly of a number of years). User agents SHOULD implement
IDNA2008 [RFC5890] and MAY implement [Unicode Technical Standard #46
<http://unicode.org/reports/tr46/>] in order to facilitate a smoother
IDNA transition. If a user agent does not implement IDNA2008, the
user agent MUST implement IDNA2003 [RFC3490].
Barth Expires April 10, 2011 [Page 16]
Internet-Draft The Web Origin Concept October 2010
11. 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.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
See Section 10.1 for an explanation why the normative
reference to an obsoleted specification is needed.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010.
Barth Expires April 10, 2011 [Page 17]
Internet-Draft The Web Origin Concept October 2010
Appendix A. Acknowledgements
Barth Expires April 10, 2011 [Page 18]
Internet-Draft The Web Origin Concept October 2010
Author's Address
Adam Barth
Google, Inc.
Email: ietf@adambarth.com
URI: http://www.adambarth.com/
Barth Expires April 10, 2011 [Page 19]