Mobile code technologies such as Java, JavaScript, and ActiveX generally limit all programs to a single restrictive security policy. However, software-based protection can allow for more extensible security models, with potentially significant performance improvements over traditional hardware-based solutions. An extensible security system should be able to protect subsystems and implement policies that are created after the initial system is shipped. We describe and analyze three strategies for interposing such security policies in software-based security systems. Implementations exist for all three strategies: several vendors have adapted capabilities to Java; JavaSoft, Netscape and Microsoft have extensions to Java's stack inspection; and we built a name space management system as an add-on to Microsoft Internet Explorer. Theoretically, all these systems are equivalently secure, but many interesting distinctions arise in practice.
This is joint work with Dan Wallach, Dirk Balfanz, and Drew Dean.
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Last modified: January 26, 1998