Internet DRAFT - draft-thomson-http-bc
draft-thomson-http-bc
Network Working Group M. Thomson
Internet-Draft Mozilla
Intended status: Standards Track G. Eriksson
Expires: May 3, 2017 C. Holmberg
Ericsson
October 30, 2016
Caching Secure HTTP Content using Blind Caches
draft-thomson-http-bc-01
Abstract
A mechanism is described whereby a server can use client-selected
shared cache.
Status of This Memo
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Table of Contents
1. Shared Caching for HTTPS . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Same-Host Secure Content Delegation . . . . . . . . . . . . . 3
2.1. Signaling Presence of a Proxy . . . . . . . . . . . . . . 3
2.2. Proxy Identification and Authentication . . . . . . . . . 4
3. Performance Optimizations . . . . . . . . . . . . . . . . . . 5
3.1. Proxy Cache Priming . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Shared Caching for HTTPS
Shared caches allow an HTTP server to offload the responsibility for
delivering certain content. Content in the shared cache can be
accessed efficiently by multiple clients, saving the origin server
from having to serve those requests and ensuring that clients receive
responses to cached requests more quickly.
Proxy caching is the most common configuration for shared caching. A
proxy cache is either explicitly configured by a client, discovered
as a result of being automatically configured.
HTTPS [RFC2818] prevents the use of proxies by creating an
authenticated end-to-end connection to the origin server or its
gateway that is authenticated. This provides a critical protection
against man-in-the-middle attacks, but it also prevents the proxy
from acting as a shared cache.
Clients do not direct queries for "https" URIs to proxies. Clients
configured with a proxy use the CONNECT pseudo-method (Section 4.3.6
of [RFC7231]) with any explicitly configured or discovered proxies to
create an end-to-end tunnel. Transparent proxies are unable to
intercept connections that are protected with TLS.
This document describes a method that enables shared caching for a
limited set of "https" resources, as selected by the server. The
server conditionally delegates the hosting of secure content to
itself. This delegation includes a marker that signals permission
for a client to send a request for an "https" resource via a proxy
rather than insisting on an end-to-end TLS connection.
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1.1. Notational Conventions
The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
document. It's not shouting; when they are capitalized, they have
the special meaning defined in [RFC2119].
This document uses the term "proxy cache" to refer to a proxy
[RFC7230] that operates an HTTP cache [RFC7234].
2. Same-Host Secure Content Delegation
The secure content delegation mechanism defined in [SCD] is used to
create a separate resource that contains encrypted and integrity
protected content. To enable caching, the primary and secondary
servers can be the same server.
A client that signals a willingness to support delegation is provided
with a response that uses a proxy-enabled out-of-band encoding that
behaves identically to the out-of-band encoding defined in
[I-D.reschke-http-oob-encoding]. The out-of-band encoding identifies
a secondary resource and implicitly indicates that the client is
willing to use a proxy and that the server allows this use. The
client is then able to request the secondary resource from a proxy
cache rather than directly to the origin server.
In this document, the origin server is able to act in the role of the
secondary server in [SCD]. However, all of the considerations that
apply to having a secondary server host content apply instead to the
proxy cache. Thus, integrity and confidentiality protections against
the proxy cache are the primary consideration.
2.1. Signaling Presence of a Proxy
Without a clear signal from the client that a caching proxy is
present, an origin server is unable to send a response with out-of-
band encoding. A value of "out-of-band" in the Accept-Encoding
header field only indicates willingness to use the secure content
delegation mechanism.
A new "oobp" content encoding is defined. The "oobp" content
encoding is identical to the "out-of-band" content encoding, with the
following additional conditions:
o A client MUST NOT signal support for "oobp" content encoding
unless it is using a proxy cache and it is willing to direct
requests to that proxy.
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o A server MUST NOT encode a response using the "oobp" content
encoding unless it permits the request to be made to a proxy
cache.
o The "oobp" content encoding MUST NOT be used to encode the
contents of a request. The "out-of-band" content encoding is
sufficient for that purpose.
Using a different content encoding name means that a resource using
secure content delegation to a secondary server [SCD] does not
inadvertently trigger a request via a proxy.
The security properties of delegation via a secondary server and via
a caching proxy are similar only to the extent that a third party is
involved. However, it might be the case that a secondary server has
a stronger relationship with the primary server and additional
constraints on its actions, such as contractual limitations. Such
constraints might make it feasible to delegate to a secondary server
selected by the primary server. A caching proxy might not be
considered acceptable in the same way.
The "oobp" content encoding clearly indicates that the client is
permitted to retrieve content from a proxy-cache.
Servers that use the "oobp" content encoding MUST include header
fields for message integrity and encryption, such as the M-I header
field [I-D.thomson-http-mice] or the Crypto-Key header field
[I-D.ietf-httpbis-encryption-encoding]. Clients MUST NOT send a
request via a proxy if these headers are not present. Absence of
these header fields indicate an error on the part of the origin
server, since integrity and confidentiality protection are mandatory.
2.2. Proxy Identification and Authentication
This mechanism does not work with a transparent caching proxy. Since
the request is made over end-to-end HTTPS in the absence of a proxy,
the feature will not be used unless the proxy is known to the client.
A proxy cache MUST therefore be expressly configured or discovered.
This produces a name and possibly a port number for the proxy. The
proxy MUST be contacted using HTTPS [RFC2818] and authenticated using
the configured or discovered domain name.
Issue: What signal do we need from the proxy cache that it supports
receiving requests with an "https://" scheme? Can we expect that
a proxy cache will happily accept a request for an HTTPS URL?
What if they ignore the scheme and send the request in the clear?
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3. Performance Optimizations
As noted in [SCD], the secondary request required by out-of-band
content encoding imposes a performance penalty. This can be
mitigated by priming clients with information about the location and
disposition of resources prior to the client making a request. A
resource map described in [SCD] might be provided to clients to
eliminate the latency involved in making requests of the origin
server for resources that might be cached.
3.1. Proxy Cache Priming
A client that makes a request of an origin server via an unprimed
proxy cache will suffer additional latency as a consequence of the
cache having to make a request to the origin server.
The following options are possible:
o Clients can speculatively make requests to a proxy cache based on
information it learns from a resource map, or from hints like the
"prefetch" link relation [HINTS]. To avoid a potential waste of
resources as a result of receiving complete responses, speculative
requests might be limited to HEAD requests; alternatively, HTTP/2
[RFC7540] flow control might be used to allow only limited
information to be sent.
o The origin server might provide the proxy cache with "prefetch"
link relations in responses to requests for secondary resources.
These link relations might identify other resources that the proxy
might retrieve speculatively. This does not improve the latency
of the initial request, but could improve subsequent requests.
4. Security Considerations
All the considerations of [SCD] apply. In particular, content that
is distributed with the assistance of a proxy cache MUST include
integrity and confidentiality protection. That means that the M-I
header field [I-D.thomson-http-mice] and the Crypto-Key header field
[I-D.ietf-httpbis-encryption-encoding] or equivalent information MUST
be present in responses that include an out-of-band content encoding.
Clients that receive a response without the information necessary to
ensure integrity and confidentiality protection against a proxy cache
MUST NOT make a request to a proxy to retrieve that response.
Clients could treat such a response as failed. Clients MAY then make
the request directly to the origin server, or - if request can be
safely retried - retry a request without the out-of-band token in the
Accept-Encoding header field.
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5. IANA Considerations
This document has no IANA actions. It should.
6. References
6.1. Normative References
[I-D.ietf-httpbis-encryption-encoding]
Thomson, M., "Encrypted Content-Encoding for HTTP", draft-
ietf-httpbis-encryption-encoding-02 (work in progress),
June 2016.
[I-D.thomson-http-mice]
Thomson, M., "Merkle Integrity Content Encoding", draft-
thomson-http-mice-01 (work in progress), June 2016.
[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>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "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>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<http://www.rfc-editor.org/info/rfc7234>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
[SCD] Ericsson, G., Holmberg, C., and M. Thomson, "An
Architecture for Secure Content Delegation using HTTP",
February 2016.
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6.2. Informative References
[HINTS] Grigorik, I., "Resource Hints", W3C TR , May 2015.
[I-D.reschke-http-oob-encoding]
Reschke, J. and S. Loreto, "'Out-Of-Band' Content Coding
for HTTP", draft-reschke-http-oob-encoding-07 (work in
progress), July 2016.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
Authors' Addresses
Martin Thomson
Mozilla
Email: martin.thomson@gmail.com
Goeran AP Eriksson
Ericsson
Email: goran.ap.eriksson@ericsson.com
Christer Holmberg
Ericsson
Email: christer.holmberg@ericsson.com
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