Network Working Group D. Druta
Internet-Draft AT&T
Intended status: Standards Track T. Fossati
Expires: April 30, 2015 Alcatel-Lucent
M. Ihlar
Ericsson
G. Klas
Vodafone
D. Lopez
Telefonica I+D
J. Reschke, Ed.
greenbytes
October 27, 2014
A Rationale for Fine-grained Intermediary-aware End-to-End Protocols
draft-reschke-objsec-00
Abstract
A tremendous growth in different uses of the Internet has led to a
growing need to protect data sent over public networks, including
data sent via HTTP. Resorting to the use of end-to-end TLS and https
for the majority of traffic looks at first like a most feasible
response. However, the more sophisticated the web architecture
becomes as it goes beyond the simple client-server model, the more
the end-to-end use of TLS shows its downside as it excludes the use
of beneficial intermediaries like caches or proxies that provide
instrumental services. The need for greater privacy seems to collide
with the equally growing desire for better end-to-end performance and
user experience. As an example, the use of TLS and https often
appears to maximise the benefit for the first but not the benefit for
the combination of both.
This document describes this dilemma and lays out a number of
objectives of what should ideally be achieved, namely catering for
sufficient security and privacy whilst providing users with the
opportunity to make use of intermediaries' services where considered
beneficial. We then introduce a number of characteristics potential
solutions could have, with the hope that those will steer us towards
suitable protocol mechanisms and data formats. End-to-end protocols
which are aware of intermediaries should enable users and/or content
providers to exercise fine-grained control over what intermediaries
shall be able to do and what exposure to data or metadata they shall
be permitted to get. The document then highlights anticipated
benefits to key stakeholders like users, content providers and
intermediaries. As elements like object security can play a useful
role, we encourage the analysis of related pieces of work in order to
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discern their applicability, limitations, and coverage of use cases.
This will allow us to frame an overall architecture and motivate more
detailed work on protocols and mechanisms in the future.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 30, 2015.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Characteristics of Solutions . . . . . . . . . . . . . . . . . 6
4. Benefits for the content provider, for the users, for the
intermediaries . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Analysis of Related Work . . . . . . . . . . . . . . . . . . . 9
6. Architectural Considerations . . . . . . . . . . . . . . . . . 10
7. Analysis of the Impacts on HTTP/2 . . . . . . . . . . . . . . 10
8. Analysis of the Impacts on TLS . . . . . . . . . . . . . . . . 10
9. Impacts on the current browser architecture . . . . . . . . . 10
10. Impacts on the existing deployment / how to make this
proposal coexist with the current . . . . . . . . . . . . . . 10
11. Privacy Impact . . . . . . . . . . . . . . . . . . . . . . . . 10
12. Security Considerations . . . . . . . . . . . . . . . . . . . 11
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
14. Informative References . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
In the last decade, the generalization of network access, the cloud
and the ubiquity of the Web as an application platform has translated
into an unprecedented increase in the use of the Internet,
facilitated by the development of new web standards and the
innovations in mobile technologies. With this growth in use, there
has been an increased amount of personal data being sent over multi
hop public links.
In order to protect the integrity and confidentiality of the online
transactions, HTTP traffic can be secured with transport layer
security using https. While https is great for e-commerce and
banking and while there is a sense of understanding in the user
community around the secure nature of https, using TLS and https for
the majority of the traffic has performance and functional drawbacks,
mainly because the HTTP session is encrypted as a whole.
Looking from the privacy and security perspective, it is clear that
users must be aware if and when an intermediary node is intercepting
their traffic and they have the right to continue or demand higher
levels of privacy by encrypting what they deem to be sensitive
information. The privacy threshold depends on user's tolerance and
the trust they put in the intermediary's reputation, as well as
whether the user is the ultimate consent authority for a given
connection: for example a parent or employer may take that role for a
connection used by a child or employee.
Modern web architecture involves sophisticated caching schemes that
involve fetching various objects (images, libraries, etc.) from
various locations in the path to avoid latency and improve the
overall user experience while reducing bandwidth use. This is an
important aspect especially in the developing countries, remote
locations and in general areas that lack fast network infrastructure.
Issues thus arise from the clash of two trends: One is towards
enhanced privacy calling for integrity, confidentiality and
anonymity. The other one is towards improved performance and lower
latency, calling for caching, compression, and adaptability.
This is also reflected in the views of important stakeholders. Users
want to make informed decisions in regards to whom they trust with
their data. They also want to have control over what data they share
with whom.
Web site owners and content providers on the other hand are keen to
get the most cost efficient and reliable way to deliver information
and services to their users and customers, while preserving their
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confidentiality, protecting their privacy and the integrity of their
data.
As different entities seek to meet the requirements of their
stakeholders, they sometimes apply solutions which generate
conflicts. Clients act on behalf of end users and solutions may
include local caches and browser proxies. Servers act on behalf of
content providers and solutions may include the use of CDNs and
reverse proxies. Intermediaries operated by communication service
providers and network operators act on behalf of users and/or content
providers and solutions include means for access network optimization
and content filtering.
In above context, the use of TLS and https looks like a "black and
white approach", or an "all or nothing" approach which doesn't lend
itself to resolving above-mentioned conflicts. The question arises:
Can "color be added"?
TLS is a client server protocol and it serves its purpose perfectly
in many client-server scenarios and use cases. But then the web has
evolved to become a mesh. Average traffic flows now involve various
intermediaries between clients and servers. They add value by
performing different functions including multiple levels of
optimization.
The application of TLS forces point-to-point flows which cuts out
intermediaries and can lead to significant drawbacks. It reduces
e.g. the optimization options which translates into increasing
traffic volumes in access networks, higher latency and overall
decreasing quality of experience for users.
It can be observed that ignoring the role of intermediaries on the
Internet does not necessarily make the Internet more secure. In
fact, in some cases it forces various parties to break the TLS
promise of e2e integrity and confidentiality in order to meet their
legal obligations (enterprises).
We suggest the solution to the challenge lies in "adding color". An
example of this are fine-grained intermediary-aware end-to-end
protocols.
Assuming the existence of such a fine-grained protocol, the following
benefits could be imagined which leads to satisfying the justified
needs of multiple stakeholders:
The ability to atomically encrypt objects or even HTTP frames should
support this sophisticated caching mechanisms while allowing content
providers to avoid distributing their server key material across the
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network nodes and prevent the risk of compromising their security.
2. Objectives
Given the short description of the problem above, the following
objectives can be derived.
1. To improve security and user-controlled privacy.
2. To minimize passive interception and man in the middle attacks.
3. To allow the client (user) and the server (content provider) to
negotiate what and whom they want to give (or not) visibility
into their traffic flows.
4. To enable multiple levels of optimization that don't conflict
with each other and either meet all parties expectations or
maximise the benefit to as many involved parties as possible.
In a world of TLS and https only, it is difficult to achieve in
particular objectives 3. and 4.
The challenge therefore is in finding mechanisms or protocols which
meet objectives 1. and 2. (e.g. in the way TLS is delivering against
those objectives) AND simultaneously provide the added flexibility to
leverage the services of 3rd party intermediaries located between
client and origin server.
3. Characteristics of Solutions
From above, one can draw some conclusions about the characteristics
possible solutions or new protocols may have to show. Below is a
non-exhaustive list. A new fine-grained intermediary-aware end-to-
end protocol may need to feature:
1. a mechanism to enable users to choose their preferred level of
privacy, adequate for a particular context and use case. The
context may be determined by the presence or absence of
particular intermediaries or proxies which offer particular
services (e.g. caching, data compression etc.).
2. mechanisms that enable certain communication data to be exchanged
securely, whereby the end user shall be able to select the set of
security services deemed adequate for a particular communication
context (e.g. confidentiality, data integrity, entity
authentication etc.).
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3. mechanisms that enable the end user to select which communication
data shall be subject to particular security services (like
confidentiality, data integrity etc.). Note that this might be
all application level data transferred between server and client,
or it might be a subset of application level data. This refers
to the notion of "fine-grained" control.
4. mechanisms that protect against passive interception and man-in-
the-middle attacks.
5. mechanisms that allow the two ultimate communication end points,
namely client and origin server, to negotiate whether and if so
which intermediaries shall be permitted to play a role in
delivering application data from origin server to client given
particular end user expectations, requirements and preferences,
and information about the status of the network between client
and server. This refers to the notion of "intermediary-aware
end-to-end protocol".
6. mechanisms that allow end users or origin server or both to
determine in real-time which traffic optimizations are available
at the time of communication setup.
7. mechanisms that allow end users or origin servers or both to
eventually select zero or more optimizations to be applied to
traffic flows between origin server and client.
8. mechanisms that allow the simultaneous or sequential application
of optimizations such that those optimizations on traffic and
traffic flow don't conflict with each other.
As said, above list is not exhaustive and additional characteristics
may be either required or useful.
The intent of this draft is not to introduce a solution yet.
However, it may help to consider possible elements which might play a
role in any solution. One element is "object security".
4. Benefits for the content provider, for the users, for the
intermediaries
An object security approach will allow the different parties to
establis end-to-end and hop-by-hop security mechanisms to different
data and metadata elements, and therefore address what can be seen as
conflicting requirements in terms of optimization and security
capabilitites.
The following benefits will arise for the different stakeholders:
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Content providers:
o Can select the type of security service that is optimal and
sufficient for particular types of content: e.g. confidentiality,
integrity protection, entity authentication etc.
o Can select which parts of their content shall be secured or not
and how content shall be securely retrievable.
o Can increase their confidence in secure temporary content storage
during delivery through encrypting/signing sensitive content
objects.
o Can leverage the business services of 3rd parties (intermediaries)
through enabling the intermediaries to perform value-added
services. Content providers may outsource particular tasks (like
caching, or offering higher security level to users) to
intermediaries.
o When using the services of content delivery networks, can benefit
from faster, optimised delivery over the "last mile" (as seen from
the perspective of a content delivery network). Content delivery
networks can optimise delivery on behalf of content providers over
the first and middle mile, however they often rely on other ISPs
and mobile network operators to deliver content over the last
mile. Intermediaries in the last mile can optimise traffic
engineering.
Users:
o Are able to enjoy sufficient privacy and security as dictated by
different use cases and equally their personal preferences (e.g.
protection from traffic analysis, integrity of content).
o Can benefit from value-added services delivered by intermediaries
on behalf of content providers.
o Can have access to services offered by intermediaries which
enhance end user quality of experience (e.g. malware detection,
parental controls).
o Can access web resources and services with lower latency and
better response times (e.g. through intermediaries performing
video pacing or traffic engineering to avoid congestion on
particular networks).
Intermediaries:
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o Can play their specific roles in content delivery and
communication on behalf of content providers, like
* Caching of content on behalf of content providers
* Optimisation of content for optimal delivery on behalf of
content providers
* Video pacing on behalf of content providers.
o Can provide value-added services on behalf of users like parental
control, malware detection etc.
o Can optimise content delivery and data communication within a
network they are associated with or control e.g. through traffic
engineering and traffic management by taking into account the
inherent needs of content types and the explicit real- and non-
real-time requirements of content providers and content delivery
networks. Thereby, intermediaries contribute to an improved "end-
to-end" user experience in the interest of both users and content
providers.
* Intermediaries are enabled to perform congestion management and
can therefore reduce latency and response times.
o Can meet regulatory requirements as they may prevail in particular
jurisdictions through an approach which is more open and
transparent to both users and content providers, and which may be
in the national interest.
5. Analysis of Related Work
The concept of object security is not something new, several
approaches targeted at different application areas exist today, and
we can even root them at the original S/MIME proposal ([RFC5751]).
As one of our first tasks, we intend to perform a detailed analysis
of this related work, producing a list of the gaps of each technology
solution in the scenarios we foresee. In particular, we have already
identified at least a couple of such related work:
o JOSE, which stands for "JSON Object Signing and Encryption". It
is a series of standards produced by the IETF under the JOSE
charter () offering
encryption, digital signatures, and Message Authentication Codes
(MACs).
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o Subresource Integrity ([SRI]), a W3C specification defining
mechanisms by which user agents may verify that a fetched resource
has been delivered without unexpected manipulation.
6. Architectural Considerations
The purpose of an object security architecture is to be able to
provide more flexible security services than strict end-to-end
encryption. A content owner should be able to express what security
levels different objects should be associated with.
Such an architecture needs to define two types of logical channels
between end-points. One channel is strictly end-to-end encrypted
where sensitive data is transferred between end points without the
risk of third-party access. The second channel is more relaxed in
allowing third-party nodes be part of the flow (i.e hop-by-hop
encrypted channel). The amount of information exposed in the second
channel is determined by the content provider alone or in agreement
with the end-user.
There are several ways to design an architecture that fulfills these
requirements. An important question to analyze is whether an object
security architecture should be designed at the application layer or
further down the stack as an alternative to TLS.
7. Analysis of the Impacts on HTTP/2
[[anchor7: TBD]]
8. Analysis of the Impacts on TLS
[[anchor9: TBD]]
9. Impacts on the current browser architecture
[[anchor11: TBD]]
10. Impacts on the existing deployment / how to make this proposal
coexist with the current
[[anchor13: TBD]]
11. Privacy Impact
[[anchor15: TBD]]
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12. Security Considerations
[[anchor17: TBD]]
13. Contributors
The following people are not listed as authors, but contributed
significantly to the discussions leading to this document: Liliana
Dinale, Vijay Gurbani, Mike Jones, Eliot Lear, Salvatore Loreto, John
Mattsson, Sanjay Mishram, Robert Moskowitz, Kevin Smith, Dan Wing.
14. Informative References
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[SRI] Braun, F., Akhawe, D., Weinberger, J., and M. West,
"Subresource Integrity", W3C Working Draft WD-SRI-
20140318, March 2014,
.
Latest version available at .
Authors' Addresses
Dan Druta
AT&T
EMail: dd5826@att.com
Thomas Fossati
Alcatel-Lucent
EMail: thomas.fossati@alcatel-lucent.com
Marcus Ihlar
Ericsson
EMail: marcus.ihlar@ericsson.com
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Guenter Klas
Vodafone
EMail: Guenter.Klas@vodafone.com
Diego R. Lopez
Telefonica I+D
EMail: diego.r.lopez@telefonica.com
Julian F. Reschke (editor)
greenbytes GmbH
EMail: julian.reschke@greenbytes.de
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