There are different methods to build an anonymity service using MIXes. A substantial decision for doing so is the method of choosing the MIX route. In this paper we compare two special configurations: a fixed MIX route used by all participants and a network of freely usable MIXes where each participant chooses his own route. The advantages and disadvantages in respect to the freedom of choice are presented and examined. We'll show that some additional attacks are possible in networks with freely chosen MIX routes. After describing these attacks, we estimate their impact on the achievable degree of anonymity. Finally, we evaluate the relevance of the described attacks with respect to existing systems like e.g. Mixmaster, Crowds, and Freedom.

A new input/output (NIO) library that provides block-oriented I/O was introduced with Java v1.4. Because of its complexity, creating network applications with the Java NIO library has been very difficult and build-in support for high-performance, distributed and parallel systems was missing. Parallel architectures are now becoming the standard in computing and Java network application programmers need a framework to build upon. In this paper, we introduce the Java NIO Framework, an extensible programming library that hides most of the NIO library details and at the same time provides support for secure and high-performance network applications. The Java NIO Framework is already used by well-known organizations, e.g. the U.S. National Institute of Standards and Technology, and is running successfully in a distributed computing framework that has more than 1000 nodes.