Jigsaw: Efficient, Low-effort Mashup Isolation

A web application often includes content from a variety of origins. Securing such a mashup application is challenging because origins often distrust each other and wish to expose narrow interfaces to their private code and data. Jigsaw is a new framework for isolating these mashup components. Jigsaw is an extension of the JavaScript language that can be run inside standard browsers using a Jigsaw-to-JavaScript compiler. Unlike prior isolation schemes that require developers to specify complex, error-prone policies, Jigsaw leverages the well-understood public/private keywords from traditional object-oriented languages, making it easy for a domain to tag internal data as externally visible. Jigsaw provides strong iframe-like isolation, but unlike previous approaches that use actual iframes as isolation containers, Jigsaw allows mutually distrusting code to run inside the same frame; this allows scripts to share state using synchronous method calls instead of asynchronous message passing. Jigsaw also introduces a novel encapsulation mechanism called surrogates. Surrogates allow domains to safely exchange objects by reference instead of by value. This improves sharing efficiency by eliminating cross-origin marshaling overhead.