Expanding and extending the security features of Java']Java

The popularity of the web has had several significant impacts, two of note here: (1) increasing sophistication of web pages, including more regular use of Java and other mobile code, and (2) decreasing average level of sophistication as the user population becomes more broad-based. Coupling these with the increased security threats posed by importing more and more mobile code has caused an emphasis on the security of executing Java applets. This paper considers two significant enhancements that will provide users with both a richer and more effective security model. The two enhancements are the provision of flexible and configurable security constraints and the ability to confine use of certain storage channels, as defined by Lampson[11], to within those constraints. We are particularly concerned with applets using files as communications channels contrary to desired security constraints. We present the mechanisms, a discussion of the implementation, and a summary of some performance comparisons. It is important to note that the ideas presented here are more generally applicable than only to the particular storage channels discussed or even only to Java.