We address the problem of establishing a group key amongst a dynamic group of users over an unreliable, or lossy, network. We term our key distribution mechanisms self-healing because users are capable of recovering lost group keys on their own, without requesting additional transmissions from the group manager, thus cutting back on network traffic, decreasing the load on the group manager, and reducing the risk of user exposure through traffic analysis. A user must be a member both before and after the session in which a particular key is sent in order to be able to recover the key through self-healing. Binding the ability to recover keys to membership status enables the group manager to use short broadcasts to establish group keys, independent of the group size. In addition, the selfhealing approach to key distribution is stateless, meaning that a group member who has been off-line for some time is able to recover new session keys immediately after coming back on-line.

We present a new solution to the problem of determining the path a packet traversed over the Internet (called the traceback problem) during a denial of service attack. This paper reframes the traceback problem as a polynomial reconstruction problem and uses algebraic techniques from coding theory and learning theory to provide robust methods of transmission and reconstruction.

Mobile code technologies such as Java, JavaScript, and ActiveX generally limit 911 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 implementation strategies for interposing such security policies in softwarebased security systems. Implementations exist for all three strategies: several vendors have adapted capabilities to Java, Netscape and Microsoft have extensions to Java's stack introspection, 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 pramtical issues and implementation details favor some aspects of each system.

Abstract