One document matched: draft-nottingham-safe-hint-01.txt
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Network Working Group M. Nottingham
Internet-Draft March 16, 2014
Intended status: Informational
Expires: September 17, 2014
The "safe" HTTP Preference
draft-nottingham-safe-hint-01
Abstract
This specification defines a "safe" preference for HTTP, expressing a
user preference to avoid "objectionable" content.
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
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This Internet-Draft will expire on September 17, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 3
2. The "safe" Preference . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 6
Appendix B. Using "safe" on Your Web Site . . . . . . . . . . . . 6
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1. Introduction
Many Web sites have a "safe" mode, to assist those who don't want to
be exposed to "objectionable" content, or who don't want their
children to be exposed to such content. YouTube [youtube], Yahoo!
Search [yahoo], Google Search [google], Bing Search [bing], and many
other services have such a setting.
However, a user that wishes to have this preference honoured would
need to go to each Web site in turn, navigate to the appropriate
page, (possibly creating an account along the way) to get a cookie
[RFC6265] set in the browser. They would need to do this for each
browser on every device they use. As has been widely noted, this is
difficult [age-privacy].
This can be onerous to nearly impossible to achieve effectively,
because there are too many permutations of sites, user agents and
devices.
If instead this preference is proactively advertised by the user
agent, things become much simpler. A user agent that supports this
(whether it be an individual browser, or through an Operating System
HTTP library) need only be configured once to assure that the
preference is advertised to all sites that understand and choose to
act upon it. It's no longer necessary to go to each site that has
potentially "unsafe" content and configure a "safe" mode.
Furthermore, a proxy (for example, at a school) can be used to ensure
that the preference is associated with all (unencrypted) requests
flowing through it, helping to assure that clients behind it are not
exposed to "objectionable" content.
This specification defines how to associate this preference with a
request, as a HTTP Preference [I-D.snell-http-prefer].
Note that this approach does not define what "safe" is; rather, it is
interpreted within the scope of each Web site that chooses to act
upon this information (or not). As such, it does not require
agreement upon what "safe" is, nor does it require application of
policy in the user agent or an intermediary (which can be problematic
for many reasons).
1.1. Notational Conventions
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].
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2. The "safe" Preference
When present in a request, the "safe" preference indicates that the
user prefers content which is not objectionable, according to the
server's definition of the concept.
For example a request that includes the "safe" preference:
GET /foo.html HTTP/1.1
Host: www.example.org
User-Agent: ExampleBrowser/1.0
Prefer: safe
When configured to do so, user agents SHOULD include the "safe"
preference in every request, to ensure that the preference is applied
(where possible) to all resources.
For example, a Web browser might have a "Request Safe Browsing"
option. additionally, other clients MAY insert it; e.g., an operating
system might choose to insert the preference in requests based upon
system-wide configuration, or a proxy might do so based upon its
configuration.
Servers that utilise the "safe" preference SHOULD document that they
do so, along with the criteria that they use to denote objectionable
content. If a site has more fine-grained degrees of "safety", it
SHOULD select a reasonable default to use, and document that; it MAY
use additional mechanisms (e.g., cookies) to fine-tune.
A response corresponding to the request above might have headers that
look like this:
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: text/html
Server: ExampleServer/2.0
Vary: Prefer
Note that the Vary response header needs to be sent if responses
associated with the resource might change depending on the value of
the "Prefer" header; this is not only true for those responses that
have changed, but also the "default" unchanged responses.
NOTE: currently, the safe preference doesn't have a payload, but one
could be used to indicate a "level" of safety desired; e.g.,
"safe=hi" or "safe=lo". Feedback appreciated.
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3. Security Considerations
The "safe" preference is not a secure mechanism; it can be inserted
or removed by intermediaries with access to the data stream. Its
presence reveals information about the user, which may be of small
assistance in "fingerprinting" the user (1 bit of information, to be
precise).
Due to its nature, including it in requests does not assure that all
content will actually be safe; it is only when servers elect to
honour it that it might change content.
Even then, a malicious server might adapt content so that it is even
less "safe" (by some definition of the word). As such, this
mechanism on its own is not enough to assure that only "safe" content
is seen; users who wish to ensure that will need to combine its use
with other techniques (e.g., content filtering).
Furthermore, the server and user may have differing ideas regarding
the semantics of "safe." As such, the "safety" of the user's
experience when browsing from site to site might (and probably will)
change.
4. IANA Considerations
This specification registers the "safe" preference
[I-D.snell-http-prefer]:
o Preference: safe
o Value: (no value)
o Description: Indicates that the user (or one responsible for them)
prefers "safe" or "unobjectionable" content.
o Reference: (this document)
o Notes:
5. References
5.1. Normative References
[I-D.snell-http-prefer] Snell, J., "Prefer Header for HTTP",
draft-snell-http-prefer-18 (work in
progress), January 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to
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Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
5.2. Informative References
[RFC6265] Barth, A., "HTTP State Management
Mechanism", RFC 6265, April 2011.
[age-privacy] Moses, A., "Privacy concern as apps share
data from kids left to their own devices",
2012, <http://www.theage.com.au/technology/
technology-news/
privacy-concern-as-apps-share-data-from-
kids-left-to-their-own-devices-20121222-
2bso6.html>.
[bing] Microsoft, "Bing Help: Block Explicit Web
Sites", 2013, <http://
onlinehelp.microsoft.com/en-AU/bing/
ff808441.aspx>.
[google] Google, "SafeSearch: turn on or off", 2013,
<http://support.google.com/websearch/bin/
answer.py?p=settings_safesearch&answer=510>.
[yahoo] Yahoo! Inc., "Yahoo! Search Preferences",
2013, <http://search.yahoo.com/preferences/
preferences>.
[youtube] Google, "How to access and turn on Safety
Mode?", 2013, <http://support.google.com/
youtube/bin/answer.py?answer=174084>.
Appendix A. Acknowledgements
Thanks to Alissa Cooper, Ilya Grigorik, Emma Llanso and Jeff Hughes
for their comments.
Appendix B. Using "safe" on Your Web Site
Web sites that allow configuration of a "safe" mode can add support
for the "safe" preference incrementally; since it will not be
supported by all clients immediately, it is necessary to still have a
"manual" safety configuration option.
When honouring the safe preference, it is important that it not be
possible to disable it through the Web UI, since "safe" may be
inserted by an intermediary (e.g., at a school) or configured and
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locked down by an administrator (e.g., a parent).
The safe preference is designed to make as much of the Web a "safe"
experience as possible; it is not intended to be configured site-by-
site. Therefore, if the user expresses a wish to disable "safe"
mode, the site should remind them that the safe preference is being
sent, and ask them to consult their administrator.
Author's Address
Mark Nottingham
EMail: mnot@mnot.net
URI: http://www.mnot.net/
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