Many researchers are investigating the use of adaptive program transformation as a way to efficiently improve program performance. Performance improving transformations are performed at runtime to adapt to the possibly changing runtime characteristics of the program. Leveraging this kind of program transformation on multiple hosts can achieve these same performance gains while reducing the overhead to apply the transformations on the local machine running the program. The reduction in overhead

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... s obtained by distributing the responsibilities for the transformation process to multiple hosts throughout the network. The use of this technology could greatly benefit applications running on networked computation nodes; however, one must first establish confidence in the secure generation and distribution of the transformed versions of the original program before acceptance and execution can occur for many network environments. Since programs are being transformed dynamically, traditional program validation methods such as checksums and digital signatures will be unable to efficiently meet the security needs of this possibly itinerant, transforming software. New validation methods must be developed in order to allow future software to avail itself of the advantages that dynamic program modification may provide while mitigating potential security risks. In this paper, we present our framework to validate dynamically-transforming software in a manner that enables the system to restrict how the software can transform as it executes on a network of hosts. Our prototype system utilizes specification languages to communicate program transformations and controls for those transformations on hosts in the *