Securing User Content in the JavaScriptable Web

OSCON 2013 Speaker Series

Recent work by a W3 Working Group plans to expose many powerful cryptographic operations for web applications. Although the planned API adds much needed functionality to JavaScript, it doesn’t address the JavaScript runtime’s terrible security properties. For instance, any script running in the web application has the power to hijack the web app’s content and UX. Just last February a mistake in Facebook’s “like” button brought down millions of web sites. Further, if you are an online service provider wanting to support higher privacy use cases like encrypted chat or web-based PGP email, the trust model is fundamentally broken since you can’t serve cryptographic JavaScript code without making the server a potential attack point.

The security challenges faced by JavaScript are mitigated by Privly, also labeled “the Web Privacy Stack,” by addressing two issues: (1) scoping code to the data, and (2) pre-distributing the code to the clients when possible.

Scoping Code to the Data

Every website has its own navigation structure, layout, and audience, but when you strip away these unique attributes of websites, you are left with data– chats, emails, photos– that can be treated uniformly across all websites. Operations on these data like encryption and signing, can be performed with indifference to their context and their contents.

Privly uses data indifference to create the notion of “Injectable Applications,” which are full web applications that are injected into the context of other web application. Since these applications are scoped to data and not layout, their properties are simplified and usable across the web.

Privly works within browser extensions by scanning web pages for specially formatted hyperlinks. When the extension detects the hyperlink, it “injects” the link into an iframe that is served locally from the browser extension.(footnote 1: This is currently how the Chrome extension performs, but different platforms are at different levels of sophistication. This approach can be universally applied to all platforms and does not necessarily require locally-served JavaScript code. However, without serving the JavaScript code locally, the security properties of the system are lost) Since the injected application is a full web application, the app could potentially support any web-implementable feature, including APIs between the host page and the injected application.

In short, if you scope an application to the data, then the cryptography can be viewed in potentially untrusted contexts.

Pre-Distributing Client Code

Privly creates an ecosystem of apps with known properties because it allows us to reason about security uniformly across the web. However, security is only as strong as the weakest attack point, which is why great care must be taken to appropriately distribute these applications. By packaging a set of applications for integration into browser extensions and mobile apps, the code is not re-loaded from a remote source every time the browser loads a new page.

Requiring the pre-distribution of applications is not normally compatible with the free and open internet. However, pains must be taken to realize the differences between the limited use cases of injected applications, and the general cases supported by web applications in general. Distributing every website to the client before visiting a website is impossible, but distributing a set of general injectable applications is lightweight and perhaps the only way to achieve security within the modern JavaScript runtime.

Requiring users to install an extension before they can view content is likely an impediment for any security system looking to gain users. However, since Privly uses hyperlinks to reference the content, it provides opportunity for a hosted fallback application. Depending on the nature of the injectable application, clicking the hyperlink could either present the same application as normally delivered by the extension, or present a prompt to install the appropriate browser extension.

Status of the System

Privly is developing under the license of a non-profit dedicated to online privacy. Versions of Privly are currently under development for Chrome, Firefox, Android, iOS, and Opera. The Chrome version is currently the most advanced, and includes functionality for contextualizing the security of injectable applications.

Attendees at our OSCON talk will be given private alpha accounts to experiment with the Privly application stack.

For more information on Privly checkout one of these resources:

Foundation Home

Central Wiki

Repository List

Development Mailing List

Testing Mailing List

Announcement Mailing List


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