Capability Myths Demolished

A nice summary of erights’ Capability Myths Demolished paper.

the morning paper

Capability Myths Demolished – Miller et. al 2003

Pretty much everyone is familiar with an ACL-based approach to security. Despite having been around for a very long time, the capabilities approach to security is less well-known. Today’s paper choice provides an excellent introduction to the capabilities model and how it compares to ACLs. Along the way we’ll learn about 7 fundamental properties of security systems, and which combinations of those are required to offer certain higher-level guarantees. Capabilities are central to the type system of the Pony language which we’ll be looking at tomorrow.

Let’s start out by looking at one of the fundamental differences between ACLs and capabilities, the direction of the relationship between subject and resource. Consider a classic access matrix such as the one below. Each row is a subject, and each column a resource. The entry in a given cell describes the permissions the subject has…

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