One document matched: draft-ietf-httpbis-http2-encryption-01.xml

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<rfc ipr="trust200902" docName="draft-ietf-httpbis-http2-encryption-01" category="exp">


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  <front>
    <title abbrev="Opportunistic HTTP Security">Opportunistic Security for HTTP</title>

    <author initials="M." surname="Nottingham" fullname="Mark Nottingham">
      <organization/>
      <address>
        <email>mnot@mnot.net</email>
        <uri>http://www.mnot.net/</uri>
      </address>
    </author>
    <author initials="M." surname="Thomson" fullname="Martin Thomson">
      <organization>Mozilla</organization>
      <address>
        <email>martin.thomson@gmail.com</email>
      </address>
    </author>

    <date year="2014"/>

    <area>General</area>
    <workgroup>HTTPbis Working Group</workgroup>
    <keyword>Internet-Draft</keyword>

    <abstract>


<t>This document describes how <spanx style="verb">http</spanx> URIs can be accessed using Transport Layer Security (TLS) to
mitigate pervasive monitoring attacks.</t>



    </abstract>


  </front>

  <middle>


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

<t>This document describes a use of HTTP Alternative Services <xref target="I-D.ietf-httpbis-alt-svc"/> to decouple
the URI scheme from the use and configuration of underlying encryption, allowing a <spanx style="verb">http</spanx> URI to be
accessed using TLS <xref target="RFC5246"/> opportunistically.</t>

<t>Currently, <spanx style="verb">https</spanx> URIs require acquiring and configuring a valid certificate, which means that
some deployments find supporting TLS difficult. Therefore, this document describes a usage model
whereby sites can serve <spanx style="verb">http</spanx> URIs over TLS without being required to support strong server
authentication.</t>

<t>Opportunistic Security <xref target="I-D.dukhovni-opportunistic-security"/> does not provide the same guarantees
as using TLS with <spanx style="verb">https</spanx> URIs; it is vulnerable to active attacks, and does not change the security
context of the connection. Normally, users will not be able to tell that it is in use (i.e., there
will be no “lock icon”).</t>

<t>By its nature, this technique is vulnerable to active attacks. A mechanism for partially mitigating
them is described in <xref target="http-tls"/>. It does not offer the same level of protection as afforded to
<spanx style="verb">https</spanx> URIs, but increases the likelihood that an active attack be detected.</t>

<section anchor="goals-and-non-goals" title="Goals and Non-Goals">

<t>The immediate goal is to make the use of HTTP more robust in the face of pervasive passive
monitoring <xref target="RFC7258"/>.</t>

<t>A secondary goal is to limit the potential for active attacks. It is not intended to offer the same
level of protection as afforded to <spanx style="verb">https</spanx> URIs, but instead to increase the likelihood that an
active attack can be detected.</t>

<t>A final (but significant) goal is to provide for ease of implementation, deployment and operation.
This mechanism should have a minimal impact upon performance, and should not require extensive
administrative effort to configure.</t>

</section>
<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="using-http-uris-over-tls" title="Using HTTP URIs over TLS">

<t>An origin server that supports the resolution of <spanx style="verb">http</spanx> URIs can indicate support for this
specification by providing an alternative service advertisement <xref target="I-D.ietf-httpbis-alt-svc"/> for a
protocol identifier that uses TLS, such as <spanx style="verb">h2</spanx> <xref target="I-D.ietf-httpbis-http2"/>.</t>

<t>A client that receives such an advertisement MAY make future requests intended for the associated
origin (<xref target="RFC6454"/>) to the identified service (as specified by <xref target="I-D.ietf-httpbis-alt-svc"/>).</t>

<t>A client that places the importance of protection against passive attacks over performance might
choose to withhold requests until an encrypted connection is available. However, if such a
connection cannot be successfully established, the client MAY resume its use of the cleartext
connection.</t>

<t>A client can also explicitly probe for an alternative service advertisement by sending a request
that bears little or no sensitive information, such as one with the OPTIONS method. Likewise,
clients with existing alternative services information could make such a request before they
expire, in order minimize the delays that might be incurred.</t>

</section>
<section anchor="auth" title="Server Authentication">

<t>By their nature, “http” URIs do not require cryptographically strong server authentication; that is
only implied by “https” URIs. Furthermore, doing so (as per <xref target="RFC2818"/>) creates a number of
operational challenges. For these reasons, server authentication is not mandatory for “http” URIs
when using the mechanism described in this specification.</t>

<t>When connecting to an alternative service for an <spanx style="verb">http</spanx> URI, clients are not required to perform the
server authentication procedure described in Section 3.1 of <xref target="RFC2818"/>. The server certificate, if
one is proffered by the alternative service, is not necessarily checked for validity, expiration,
issuance by a trusted certificate authority or matched against the name in the URI. Therefore, the
alternative service MAY provide any certificate, or even select TLS cipher suites that do not
include authentication.</t>

<t>A client MAY perform additional checks on the offered certificate if the server does not select an
unauthenticated TLS cipher suite.  This document doesn’t define any such checks, though clients
could be configured with a policy that defines what is acceptable.</t>

<t>As stipulated by <xref target="I-D.ietf-httpbis-alt-svc"/>, clients MUST NOT use alternative services with a
host other than the origin’s, unless the alternative service itself is strongly authenticated (as
the origin’s host); for example, using TLS with a certificate that validates as per <xref target="RFC2818"/>.</t>

</section>
<section anchor="interaction-with-https-uris" title="Interaction with “https” URIs">

<t>When using alternative services, both <spanx style="verb">http</spanx> and <spanx style="verb">https</spanx> URIs might use the same connection,
because HTTP/2 permits requests for multiple origins on the same connection.</t>

<t>Since <spanx style="verb">https</spanx> URIs rely on server authentication, a connection that is initially created for <spanx style="verb">http</spanx>
URIs without authenticating the server cannot be used for <spanx style="verb">https</spanx> URIs until the server certificate
is successfully authenticated. Section 3.1 of <xref target="RFC2818"/> describes the basic mechanism, though the
authentication considerations in <xref target="I-D.ietf-httpbis-alt-svc"/> also apply.</t>

<t>Connections that are established without any means of server authentication (for instance, the
purely anonymous TLS cipher suites), cannot be used for <spanx style="verb">https</spanx> URIs.</t>

</section>
<section anchor="http-tls" title="Requiring Use of TLS">

<t>Editors’ Note: this is a very rough take on an approach that would provide a limited form of
protection against downgrade attack. It’s unclear at this point whether the additional effort (and
modest operational cost) is worthwhile.</t>

<t>The mechanism described in this specification is trival to mount an active attack against, for two
reasons:</t>

<t><list style="symbols">
  <t>A client that doesn’t perform authentication an easy victim of server impersonation, through
man-in-the-middle attacks.</t>
  <t>A client that is willing to use cleartext to resolve the resource will do so if access to any
TLS-enabled alternative services is blocked at the network layer.</t>
</list></t>

<t>Given that the primary goal of this specification is to prevent passive attacks, these are not
critical failings (especially considering the alternative - HTTP over cleartext). However, a modest
form of protection against active attacks can be provided for clients on subsequent connections.</t>

<t>When an alternative service is able to commit to providing service for a particular origin over TLS
for a bounded period of time, clients can choose to rely upon its avilability, failing when it
cannot be contacted. Effectively, this makes the choice to use a secured protocol “sticky” in the
client.</t>

<section anchor="the-http-tls-header-field" title="The HTTP-TLS Header Field">

<t>A alternative service can make this commitment by sending a <spanx style="verb">HTTP-TLS</spanx> header field:</t>

<figure><artwork><![CDATA[

HTTP-TLS     = 1#parameter
]]></artwork></figure>

<t>When it appears in a HTTP response from a strongly authenticated alternative service, this header
field indicates that the availability of the origin through TLS-protected alternative services is
“sticky”, and that the client MUST NOT fall back to cleartext protocols while this information is
considered fresh.</t>

<t>For example:</t>

<figure><artwork><![CDATA[

GET /index.html HTTP/1.1
Host: example.com


HTTP/1.1 200 OK
Content-Type: text/html
Cache-Control: 600
Age: 30
Date: Thu, 1 May 2014 16:20:09 GMT
HTTP-TLS: ma=3600
]]></artwork></figure>

<t>This header field creates a commitment from the origin <xref target="RFC6454"/> of the associated resource (in
the example, <spanx style="verb">http://example.com</spanx>).  For the duration of the commitment, clients SHOULD strongly
authenticate the server for all subsequent requests made to that origin, though this creates some
risks for clients <xref target="pinrisks"/>.</t>

<t>Authentication for HTTP over TLS is described in Section 3.1 of <xref target="RFC2818"/>, noting the additional
requirements in <xref target="I-D.ietf-httpbis-alt-svc"/>. The header field MUST be ignored if strong
authentication fails; otherwise, an attacker could create a persistent denial of service by
falsifying a commitment.</t>

<t>The commitment to use authenticated TLS persists for a period determined by the value of the <spanx style="verb">ma</spanx>
parameter. See Section 4.2.3 of <xref target="RFC7234"/> for details of determining response age.</t>

<figure><artwork><![CDATA[

ma-parameter     = delta-seconds
]]></artwork></figure>

<t>The commitment made by the <spanx style="verb">HTTP-TLS</spanx> header field applies only to the origin of the resource that
generates the <spanx style="verb">HTTP-TLS</spanx> header field.  Requests for an origin that has a persisted, unexpired value
for <spanx style="verb">HTTP-TLS</spanx> MUST fail if they cannot be made over an authenticated TLS connection.</t>

<t>Note that the commitment is not bound to a particular alternative service.  Clients SHOULD use
alternative services that they become aware of.  However, clients MUST NOT use an unauthenticated
alternative service for an origin with this commitment.  Where there is an active commitment,
clients MAY instead ignore advertisements for unsecured alternatives services.</t>

</section>
<section anchor="pinrisks" title="Operational Considerations">

<t>To avoid situations where a persisted value of <spanx style="verb">HTTP-TLS</spanx> causes a client to be unable to contact a
site, clients SHOULD limit the time that a value is persisted for a given origin. A lower limit
might be appropriate for initial observations of <spanx style="verb">HTTP-TLS</spanx>; the certainty that a site has set a
correct value - and the corresponding limit on persistence - can increase as the value is seen more
over time.</t>

<t>Once a server has indicated that it will support authenticated TLS, a client MAY use key pinning
<xref target="I-D.ietf-websec-key-pinning"/> or any other mechanism that would otherwise be restricted to use
with “https” URIs, provided that the mechanism can be restricted to a single HTTP origin.</t>

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

<section anchor="security-indicators" title="Security Indicators">

<t>User Agents MUST NOT provide any special security indicia when an <spanx style="verb">http</spanx> resource is acquired using
TLS. In particular, indicators that might suggest the same level of security as <spanx style="verb">https</spanx> MUST NOT be
used (e.g., using a “lock device”).</t>

</section>
<section anchor="downgrade" title="Downgrade Attacks">

<t>A downgrade attack against the negotiation for TLS is possible. With the <spanx style="verb">HTTP-TLS</spanx> header field,
this is limited to occasions where clients have no prior information (see <xref target="privacy"/>), or when
persisted commitments have expired.</t>

<t>For example, because the <spanx style="verb">Alt-Svc</spanx> header field <xref target="I-D.ietf-httpbis-alt-svc"/> likely appears in an
unauthenticated and unencrypted channel, it is subject to downgrade by network attackers. In its
simplest form, an attacker that wants the connection to remain in the clear need only strip the
<spanx style="verb">Alt-Svc</spanx> header field from responses.</t>

<t>Downgrade attacks can be partially mitigated using the <spanx style="verb">HTTP-TLS</spanx> header field, because when it is
used, a client can avoid using cleartext to contact a supporting server. However, this only works
when a previous connection has been established without an active attacker present; a continuously
present active attacker can either prevent the client from ever using TLS, or offer its own
certificate.</t>

</section>
<section anchor="privacy" title="Privacy Considerations">

<t>Cached alternative services can be used to track clients over time; e.g., using a user-specific
hostname. Clearing the cache reduces the ability of servers to track clients; therefore clients
MUST clear cached alternative service information when clearing other origin-based state (i.e.,
cookies).</t>

</section>
<section anchor="confusion-regarding-request-scheme" title="Confusion Regarding Request Scheme">

<t>Many existing HTTP/1.1 implementations use the presence or absence of TLS in the stack to determine
whether requests are for <spanx style="verb">http</spanx> or <spanx style="verb">https</spanx> resources.  This is necessary in many cases because the
most common form of an HTTP/1.1 request does not carry an explicit indication of the URI scheme.</t>

<t>HTTP/1.1 MUST NOT be sent over HTTP/1.1 or earlier versions of the protocol.  Opportunistically
secured HTTP requests MUST include an explicit scheme identifier.</t>

</section>
</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="RFC2818">

<front>
<title>HTTP Over TLS</title>
<author initials="E." surname="Rescorla" fullname="E. Rescorla">
<organization/></author>
<date year="2000" month="May"/>
<abstract>
<t>This memo describes how to use Transport Layer Security (TLS) to secure Hypertext Transfer Protocol (HTTP) connections over the Internet.  This memo provides information for the Internet community.</t></abstract></front>

<seriesInfo name="RFC" value="2818"/>
<format type="TXT" octets="15170" target="http://www.rfc-editor.org/rfc/rfc2818.txt"/>
</reference>



<reference anchor="RFC5246">

<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
<author initials="T." surname="Dierks" fullname="T. Dierks">
<organization/></author>
<author initials="E." surname="Rescorla" fullname="E. Rescorla">
<organization/></author>
<date year="2008" month="August"/>
<abstract>
<t>This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol.  The TLS protocol provides communications security over the Internet.  The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK]</t></abstract></front>

<seriesInfo name="RFC" value="5246"/>
<format type="TXT" octets="222395" target="http://www.rfc-editor.org/rfc/rfc5246.txt"/>
</reference>



<reference anchor="RFC6454">

<front>
<title>The Web Origin Concept</title>
<author initials="A." surname="Barth" fullname="A. Barth">
<organization/></author>
<date year="2011" month="December"/>
<abstract>
<t>This document defines the concept of an "origin", which is often used as the scope of authority or privilege by user agents.  Typically, user agents isolate content retrieved from different origins to prevent malicious web site operators from interfering with the operation of benign web sites.  In addition to outlining the principles that underlie the concept of origin, this document details how to determine the origin of a URI and how to serialize an origin into a string.  It also defines an HTTP header field, named "Origin", that indicates which origins are associated with an HTTP request. [STANDARDS-TRACK]</t></abstract></front>

<seriesInfo name="RFC" value="6454"/>
<format type="TXT" octets="41363" target="http://www.rfc-editor.org/rfc/rfc6454.txt"/>
</reference>



<reference anchor="RFC7234">

<front>
<title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
<author initials="R." surname="Fielding" fullname="R. Fielding">
<organization/></author>
<author initials="M." surname="Nottingham" fullname="M. Nottingham">
<organization/></author>
<author initials="J." surname="Reschke" fullname="J. Reschke">
<organization/></author>
<date year="2014" month="June"/>
<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="RFC" value="7234"/>
<format type="TXT" octets="90647" target="http://www.rfc-editor.org/rfc/rfc7234.txt"/>
</reference>



<reference anchor="I-D.ietf-httpbis-http2">
<front>
<title>Hypertext Transfer Protocol version 2</title>

<author initials="M" surname="Belshe" fullname="Mike Belshe">
    <organization/>
</author>

<author initials="R" surname="Peon" fullname="Roberto Peon">
    <organization/>
</author>

<author initials="M" surname="Thomson" fullname="Martin Thomson">
    <organization/>
</author>

<date month="November" day="29" year="2014"/>

<abstract><t>This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP).  HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent messages on the same connection.  It also introduces unsolicited push of representations from servers to clients.  This specification is an alternative to, but does not obsolete, the HTTP/1.1 message syntax.  HTTP's existing semantics remain unchanged.</t></abstract>

</front>

<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-http2-16"/>
<format type="TXT" target="http://www.ietf.org/internet-drafts/draft-ietf-httpbis-http2-16.txt"/>
</reference>



<reference anchor="I-D.ietf-httpbis-alt-svc">
<front>
<title>HTTP Alternative Services</title>

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

<author initials="P" surname="McManus" fullname="Patrick McManus">
    <organization/>
</author>

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

<date month="December" day="1" year="2014"/>

<abstract><t>This document specifies "alternative services" for HTTP, which allow an origin's resources to be authoritatively available at a separate network location, possibly accessed with a different protocol configuration.</t></abstract>

</front>

<seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-alt-svc-05"/>
<format type="TXT" target="http://www.ietf.org/internet-drafts/draft-ietf-httpbis-alt-svc-05.txt"/>
</reference>



<reference anchor="I-D.ietf-websec-key-pinning">
<front>
<title>Public Key Pinning Extension for HTTP</title>

<author initials="C" surname="Evans" fullname="Chris Evans">
    <organization/>
</author>

<author initials="C" surname="Palmer" fullname="Chris Palmer">
    <organization/>
</author>

<author initials="R" surname="Sleevi" fullname="Ryan Sleevi">
    <organization/>
</author>

<date month="October" day="5" year="2014"/>

<abstract><t>This document defines a new HTTP header that allows web host operators to instruct user agents to remember ("pin") the hosts' cryptographic identities over a period of time.  During that time, UAs will require that the host presents a certificate chain including at least one Subject Public Key Info structure whose fingerprint matches one of the pinned fingerprints for that host.  By effectively reducing the number of trusted authorities who can authenticate the domain during the lifetime of the pin, pinning may reduce the incidence of man-in-the-middle attacks due to compromised Certification Authorities.</t></abstract>

</front>

<seriesInfo name="Internet-Draft" value="draft-ietf-websec-key-pinning-21"/>
<format type="TXT" target="http://www.ietf.org/internet-drafts/draft-ietf-websec-key-pinning-21.txt"/>
</reference>




    </references>

    <references title="Informative References">





<reference anchor="I-D.dukhovni-opportunistic-security">
<front>
<title>Opportunistic Security: Some Protection Most of the Time</title>

<author initials="V" surname="Dukhovni" fullname="Viktor Dukhovni">
    <organization/>
</author>

<date month="November" day="26" year="2014"/>

<abstract><t>This document defines the concept "Opportunistic Security" in the context of communications protocols.  Protocol designs based on Opportunistic Security use encryption even when authentication is not available, and use authentication when possible, thereby removing barriers to the widespread use of encryption on the Internet.</t></abstract>

</front>

<seriesInfo name="Internet-Draft" value="draft-dukhovni-opportunistic-security-06"/>
<format type="TXT" target="http://www.ietf.org/internet-drafts/draft-dukhovni-opportunistic-security-06.txt"/>
</reference>



<reference anchor="RFC7258">

<front>
<title>Pervasive Monitoring Is an Attack</title>
<author initials="S." surname="Farrell" fullname="S. Farrell">
<organization/></author>
<author initials="H." surname="Tschofenig" fullname="H. Tschofenig">
<organization/></author>
<date year="2014" month="May"/>
<abstract>
<t>Pervasive monitoring is a technical attack that should be mitigated in the design of IETF protocols, where possible.</t></abstract></front>

<seriesInfo name="BCP" value="188"/>
<seriesInfo name="RFC" value="7258"/>
<format type="TXT" octets="13396" target="http://www.rfc-editor.org/rfc/rfc7258.txt"/>
</reference>




    </references>


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

<t>Thanks to Patrick McManus, Eliot Lear, Stephen Farrell, Guy Podjarny, Stephen Ludin, Erik Nygren,
Paul Hoffman, Adam Langley, Eric Rescorla and Richard Barnes for their feedback and suggestions.</t>

</section>


  </back>
</rfc>