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[liberationtech] New web privacy system could revolutionize the safety of surfing

Yosem Companys companys at
Sun Oct 5 17:06:24 PDT 2014

Researchers from UCL, Stanford Engineering, Google, Chalmers and
Mozilla Research have built a new system that protects Internet users'
privacy whilst increasing the flexibility for web developers to build
web applications that combine data from different web sites,
dramatically improving the safety of surfing the web.

The system, 'Confinement with Origin Web Labels,' or COWL, works with
Mozilla's Firefox and the open-source version of Google's Chrome web
browsers and prevents malicious code in a web site from leaking
sensitive information to unauthorised parties, whilst allowing code in
a web site to display content drawn from multiple web sites – an
essential function for modern, feature-rich web applications.

Testing of COWL prototypes for the Chrome and Firefox web browsers
shows the system provides strong security without perceptibly slowing
the loading speed of web pages. Following its announcement today, COWL
will be freely available for download and use on 15th October from The team who developed it, including two PhD students
from Stanford (working in collaboration with Mozilla Research) and a
recently graduated PhD from UCL (now employed by Google), hope COWL
will be widely adopted by web developers.

Currently, web users' privacy can be compromised by malicious
JavaScript code hidden in seemingly legitimate web sites. The web
site's operator may have incorporated code obtained elsewhere into his
or her web site without realising that the code contains bugs or is
malicious. Such code can access sensitive data within the same or
other browser tabs, allowing unauthorised parties to obtain or modify
data without the user's knowledge.

The research team describe COWL in a paper that will appear in the
Proceedings of the 11th USENIX Symposium on Operating Systems Design
and Implementation, a premier venue for operating systems research.

Co-author Professor Brad Karp (UCL Computer Science), said: "COWL
achieves both privacy for the user and flexibility for the web
application developer. Achieving both these aims, which are often in
opposition in many system designs, is one of the central challenges in
computer systems security research.

"The new system provides a property known as 'confinement' which has
been known since the 1970s, but proven difficult to achieve in
practical systems like web browsers. COWL confines JavaScript programs
that run within the browser, such as in separate tabs. If a JavaScript
program embedded within one web site reads information provided by
another web site – legitimately or otherwise – COWL permits the data
to be shared, but thereafter restricts the application receiving the
information from communicating it to unauthorised parties. As a
result, the site that shares data maintains control over it, even
after sharing the information within the browser."

Co-author Professor David Mazières (Stanford University Computer
Science), said: "Security mechanisms for the web must keep pace with
the web's rapid evolution. Current measures, such as the Same Origin
Policy (SOP), work by stopping JavaScript programs embedded within one
web site – malicious or otherwise – from reading data hosted by a
separate web site. This brittle approach doesn't work for modern
so-called 'mashup' applications that combine information from multiple
web sites. Essentially, the SOP doesn't fit how many web sites are
built today. And prior attempts at weakening the SOP to allow this
sort of sharing, such as with Cross-Origin Resource Sharing (CORS),
make it trivial for malicious code to leak sensitive data to
unauthorised parties."

When building a modern web site, web developers routinely incorporate
JavaScript library code written by third-party authors of unknowable
intent. The study cites measurements indicating that 59% of the top
one million web sites and 77% of the top 10,000 web sites incorporate
a JavaScript library written by a third party. The team say such
inclusion of JavaScript libraries is dangerous, as although the code
includes features the web developers want, it might also contain
malicious code that steals the browser user's data. In such cases, the
SOP cannot protect sensitive data, as the included library is hosted
by the same web site origin (i.e., under the same Internet domain

Professor Karp said: "By blocking the building of web applications
that synthesize content from multiple web sites, the SOP actually
forces web developers to make design choices that put users' privacy
at risk. That's a problem we've solved with COWL.

"For example, one useful web application would let users check they're
not being overcharged for items they've ordered from Amazon. The app
would have to pull in information from the user's bank statement and
Amazon, reconcile the two, and present the result in the browser. To
do this, a web developer would need to write code that integrated data
from the bank's web site with data from Amazon's web site but the SOP
would block this, as the two data sources are hosted by different web
domain names. Today's web developers get around this by writing an app
that asks the user for their bank and Amazon login credentials, so it
can log into both services and collect information as if it is the
user. This clearly compromises the user's privacy as the provider of
the app gains full access to the user's online banking system and
Amazon account."

Deian Stefan, lead PhD student on the project at Stanford, said: "What
we've achieved in COWL is a system that lets web developers build
feature-rich applications that combine data from different web sites
without requiring that users share their login details directly with
third-party web applications, all while ensuring that the user's
sensitive data seen by such an application doesn't leave the browser.
Both web developers and users win."

The research team has shown how to use COWL to build four applications
previously unachievable with strong privacy, including an encrypted
document editor, a third-party mashup application, a password manager,
and a web site that safely includes an untrusted third-party library.
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