One document matched: draft-nottingham-safe-hint-02.xml

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<rfc ipr="trust200902" docName="draft-nottingham-safe-hint-02" category="info">

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  <front>
    <title abbrev="safe browsing preference">The "safe" HTTP Preference</title>

    <author initials="M." surname="Nottingham" fullname="Mark Nottingham">
      <organization></organization>
      <address>
        <email>mnot@mnot.net</email>
        <uri>http://www.mnot.net/</uri>
      </address>
    </author>

    <date year="2014"/>

    <area>General</area>
    
    <keyword>safe</keyword> <keyword>preference</keyword> <keyword>child-protection</keyword>

    <abstract>


<t>This specification defines a “safe” preference for HTTP, expressing a user
preference to avoid “objectionable” content.</t>



    </abstract>


  </front>

  <middle>


<section anchor="introduction" title="Introduction">

<t>Many Web sites have a “safe” mode, to assist those who don’t want to be exposed
(or have their children exposed) to “objectionable” content. YouTube
<xref target="youtube"/>, Yahoo! Search <xref target="yahoo"/>, Google Search <xref target="google"/>, Bing Search
<xref target="bing"/>, and many other services have such a setting.</t>

<t>However, those who wish to have this preference honoured 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 <xref target="RFC6265"/> set in the browser. They would need
to do this for each browser on every device they use. </t>

<t>This is onerous to achieve effectively, because there are so many permutations
of sites, user agents and devices.</t>

<t>If this preference is proactively advertised by the user agent, things become
much simpler. A user agent that supports doing so (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.</t>

<t>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.</t>

<t>This specification defines how to associate this preference with a request,
as a HTTP Preference <xref target="I-D.snell-http-prefer"/>.</t>

<t>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).</t>

<section anchor="notational-conventions" title="Notational Conventions">

<t>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 <xref target="RFC2119"/>.</t>

</section>
</section>
<section anchor="safe" title="The “safe” Preference">

<t>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. </t>

<t>For example, a request that includes the “safe” preference:</t>

<figure><artwork><![CDATA[
GET /foo.html HTTP/1.1
Host: www.example.org
User-Agent: ExampleBrowser/1.0
Prefer: safe
]]></artwork></figure>

<t>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.</t>

<t>For example, a Web browser might have a “Request Safe Browsing”
option. </t>

<t>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.</t>

<t>Origin servers that utilize the “safe” preference SHOULD document that they do
so, along with the criteria that they use to denote objectionable content. If a
server 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.</t>

<t>A response corresponding to the request above might have headers that look
like this:</t>

<figure><artwork><![CDATA[
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Content-Type: text/html
Server: ExampleServer/2.0
Vary: Prefer
]]></artwork></figure>

<t>Note that the Vary response header needs to be sent if cacheable responses
associated with the resource might change depending on the value of the
“Prefer” header. This is not only true for those responses that are “safe”,
but also the default “unsafe” response.</t>

<t>See <xref target="I-D.ietf-httpbis-p6-cache"/> for more information.</t>

</section>
<section anchor="security-considerations" title="Security Considerations">

<t>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).</t>

<t>Due to its nature, including “safe” in requests does not assure that all
content will actually be safe; it is only when servers elect to honour it that
content might be “safe”.</t>

<t>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).</t>

<t>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. </t>

</section>
<section anchor="iana-considerations" title="IANA Considerations">

<t>This specification registers the “safe” preference
<xref target="I-D.snell-http-prefer"/>:</t>

<t><list style="symbols">
  <t>Preference: safe</t>
  <t>Value: (no value)</t>
  <t>Description: Indicates that the user (or one responsible for them) prefers
“safe” or “unobjectionable” content.</t>
  <t>Reference: (this document)</t>
  <t>Notes: </t>
</list></t>

</section>


  </middle>

  <back>

    <references title='Normative References'>





<reference anchor='RFC2119'>

<front>
<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street></postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email></address></author>
<date year='1997' month='March' />
<area>General</area>
<keyword>keyword</keyword>
<abstract>
<t>
   In many standards track documents several words are used to signify
   the requirements in the specification.  These words are often
   capitalized.  This document defines these words as they should be
   interpreted in IETF documents.  Authors who follow these guidelines
   should incorporate this phrase near the beginning of their document:

<list>
<t>
      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.
</t></list></t>
<t>
   Note that the force of these words is modified by the requirement
   level of the document in which they are used.
</t></abstract></front>

<seriesInfo name='BCP' value='14' />
<seriesInfo name='RFC' value='2119' />
<format type='TXT' octets='4723' target='http://www.rfc-editor.org/rfc/rfc2119.txt' />
<format type='HTML' octets='17970' target='http://xml.resource.org/public/rfc/html/rfc2119.html' />
<format type='XML' octets='5777' target='http://xml.resource.org/public/rfc/xml/rfc2119.xml' />
</reference>



<reference anchor='I-D.snell-http-prefer'>
<front>
<title>Prefer Header for HTTP</title>

<author initials='J' surname='Snell' fullname='James Snell'>
    <organization />
</author>

<date month='January' day='7' year='2013' />

<abstract><t>This specification defines an HTTP header field that can be used by a client to request that certain behaviors be employed by a server while processing a request.</t></abstract>

</front>

<seriesInfo name='Internet-Draft' value='draft-snell-http-prefer-18' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-snell-http-prefer-18.txt' />
</reference>




    </references>

    <references title='Informative References'>





<reference anchor='RFC6265'>

<front>
<title>HTTP State Management Mechanism</title>
<author initials='A.' surname='Barth' fullname='A. Barth'>
<organization /></author>
<date year='2011' month='April' />
<abstract>
<t>This document defines the HTTP Cookie and Set-Cookie header fields.  These header fields can be used by HTTP servers to store state (called cookies) at HTTP user agents, letting the servers maintain a stateful session over the mostly stateless HTTP protocol.  Although cookies have many historical infelicities that degrade their security and privacy, the Cookie and Set-Cookie header fields are widely used on the Internet.  This document obsoletes RFC 2965. [STANDARDS-TRACK]</t></abstract></front>

<seriesInfo name='RFC' value='6265' />
<format type='TXT' octets='79724' target='http://www.rfc-editor.org/rfc/rfc6265.txt' />
</reference>



<reference anchor='I-D.ietf-httpbis-p6-cache'>
<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>

<author initials='R' surname='Fielding' fullname='Roy Fielding'>
    <organization />
</author>

<author initials='M' surname='Nottingham' fullname='Mark Nottingham'>
    <organization />
</author>

<author initials='J' surname='Reschke' fullname='Julian Reschke'>
    <organization />
</author>

<date month='February' day='6' year='2014' />

<abstract><t>The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems.  This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages.</t></abstract>

</front>

<seriesInfo name='Internet-Draft' value='draft-ietf-httpbis-p6-cache-26' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-ietf-httpbis-p6-cache-26.txt' />
</reference>


<reference anchor="yahoo" target="http://search.yahoo.com/preferences/preferences">
  <front>
    <title>Yahoo! Search Preferences</title>
    <author >
      <organization>Yahoo! Inc.</organization>
    </author>
    <date year="2013"/>
  </front>
</reference>
<reference anchor="bing" target="http://onlinehelp.microsoft.com/en-AU/bing/ff808441.aspx">
  <front>
    <title>Bing Help: Block Explicit Web Sites</title>
    <author >
      <organization>Microsoft</organization>
    </author>
    <date year="2013"/>
  </front>
</reference>
<reference anchor="google" target="http://support.google.com/websearch/bin/answer.py?p=settings_safesearch&answer=510">
  <front>
    <title>SafeSearch: turn on or off</title>
    <author >
      <organization>Google</organization>
    </author>
    <date year="2013"/>
  </front>
</reference>
<reference anchor="youtube" target="http://support.google.com/youtube/bin/answer.py?answer=174084">
  <front>
    <title>How to access and turn on Safety Mode?</title>
    <author >
      <organization>Google</organization>
    </author>
    <date year="2013"/>
  </front>
</reference>


    </references>


<section anchor="acknowledgements" title="Acknowledgements">

<t>Thanks to Alissa Cooper, Ilya Grigorik, Emma Llanso, Jeff Hughes and Loorie
Cranor for their comments.</t>

</section>
<section anchor="setting-safe-from-web-browsers" title="Setting “safe” from Web Browsers">

<t>As discussed in <xref target="safe"/>, there are many possible ways for the “safe”
preference to be generated. One possibility is for a Web browser to allow its
users to configure the preference to be sent.</t>

<t>When doing so, it is important not to misrepresent the preference as binding to Web sites. For example, an appropriate setting might be a checkbox with wording such as:</t>

<figure><artwork><![CDATA[
  [] Request "safe" content from Web sites
]]></artwork></figure>

<t>… along with further information available upon request (e.g., from a “help”
system).</t>

<t>Browsers might also allow the “safe” preference to be “locked” – that is,
prevent modification without administrative access, or a passcode.</t>

</section>
<section anchor="using-safe-on-your-web-site" title="Using “safe” on Your Web Site">

<t>Web sites that allow configuration of a “safe” mode (for example, using a
cookie) can add support for the “safe” preference incrementally; since the
preference will not be supported by all clients immediately, it is necessary to
still have a fallback configuration option.</t>

<t>When honouring the safe preference, it is important that it not be possible to
disable it through the Web interface, since “safe” may be inserted by an
intermediary (e.g., at a school) or configured and locked down by an
administrator (e.g., a parent). When both the “safe” preference and per-site
configuration are present, the preference takes precedence.</t>

<t>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 (since “safe” might be set by an intermediary or locked-down
Operating System configuration).</t>

<t>As explained in <xref target="safe"/>, responses that change based upon the presence of the
“safe” preference need to either carry the “Vary: Prefer” response header
field, or be uncacheable by shared caches (e.g., with a “Cache-Control:
private” response header field). This is to avoid an unsafe cached response
being served to a client that prefers safe content (or vice versa).</t>

</section>


  </back>
</rfc>