Modules in wyvern: advanced control over security and privacy.

In today's systems, restricting the authority of untrusted code is difficult because, by default, code has the same authority as the user running it. Object capabilities are a promising way to implement the principle of least authority, but being too low-level and fine-grained, take away many conveniences provided by module systems. We present a module system design that is capability-safe, yet preserves most of the convenience of conventional module systems. We demonstrate how to ensure key security and privacy properties of a program as a mode of use of our module system. Our authority safety result formally captures the role of mutable state in capability-based systems and uses a novel non-transitive notion of authority, which allows us to reason about authority restriction: the encapsulation of a stronger capability inside a weaker one.