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Our experiments with IEEE 802.11b based wireless ad hoc networks show that neighbor sensing with broadcast messages introduces "communication gray zones": in such zones data messages cannot be exchanged although the HELLO messages indicate neighbor reachability. This leads to a systematic mismatch between the route state and the real world connectivity, resulting in disruptive behavior for some ad hoc routing protocols. Concentrating on AODV we explore this issue and evaluate three different techniques to overcome the gray zone problem. We present quantitative measurements of these improvements and discuss the consequences for ad hoc routing protocols and their implementations.

Mobile code technology has become a driving force for recent advances in distributed systems. The concept of mobility of executable code raises major security problems. In this paper we deal with the protection of mobile code from possibly malicious hosts. We conceptualize on the specific cryptographic problems posed by mobile code. We are able to provide a solution for some of these problems: We present techniques how to achieve "non-interactive evaluation with encrypted functions" in certain cases and give a complete solution for this problem in important instances. We further present a way how an agent might securely perform a cryptographic primitive, digital signing, in an untrusted execution environment. Our results are based on the use of homomorphic encryption schemes and function composition techniques.

We have built an Ad hoc Protocol Evaluation testbed (APE) in order to perform large-scale, reproducible experiments. APE aims at assessing several different routing protocols in a real world environment instead of by simulation. We present the APE testbed architecture and report on initial experiments with up to 37 physical nodes that show the reproducibility and scalability of our approach. Several scenario scripts have been written that include strict choreographic instructions to the testers who walk around with ORiNOCO equipped laptops. We introduce a metric called Virtual Mobility that we use to compare different testruns. This metric is based on the measured signal quality instead of the geometric distance between nodes, hence it reflects how a routing protocol actually perceives the network's dynamics.

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