Enhanced security for mobile agent systems.

摘要

Mobile agents are an application design scheme for distributed systems that combine mobile code principles with software agents. Mobile computing emerged over the last decade with a vision for code that changes its execution location---moving from platform to platform in a heterogeneous network carrying an embodied, updatable state. Agents are software processes that act on a user's behalf, perform particular functions autonomously, and interact with their environment to accomplish their goals. We consider in this thesis historical mobile agent security research while also gauging current trends.; Program mobility and autonomy are ultimate distributed computing expressions---programmers can view the network as a seamless canvas for application development. Disconnected host operations give a key advantage to mobile agents; however, researchers agree that protecting a stand-alone autonomous mobile agent with software-only approaches remains difficult. In this thesis, we produce several results that enhance mobile agent security and provide generalized code protection. We propose and define several novel techniques that protect mobile agents in ubiquitous environments and that solve practical problems in the program obfuscation field. We contribute to the field in the following ways:; Generalized black box program protection. We provide a novel technique for hiding a candidate program's input/output relationships by using a data encryption padding technique. This method provides general program/circuit protection and relies on the semantic security strength found in common data encryption ciphers. Analyzing the black box relations for such protected programs cannot reproduce the original program's input/output mapping.; Generalized white box program protection. We semantically protect the white-box source code/gate structure information for a relevant program class defined by bounded input size. By using simple Boolean canonical circuit forms, we create an obfuscation technique that effectively hides all information regarding the source code or circuit gate structure.; Embedded-key program protection. Leveraging our white-box results, we demonstrate how to embed an encryption key in programs that have small input size with measurable security. This technique gives foundations for solving the classic computer security problem regarding how transform any private-key cryptosystem into a public-key cryptosystem.; Analyzing mobile code protection schemes for code privacy. The Virtual Black Box (VBB) has been a theoretical foundation for understanding obfuscation strength for some time. We consider programmatic intent protection for mobile agents and pose a new model for obfuscated code security based on random programs.; Tamperproofing mobile code. We lay foundations for a new code protection methodology for mobile agents based on techniques used in the data encryption field. Specifically, we employ circuit encryption techniques that use combined sub-circuit permutation and substitution. As a result, we appeal to indistinguishability notions for circuits drawn uniformly from large sets and establish properties for obfuscators that provide intent protection based on randomization.; Trust framework for mobile agents. Security tends to be Boolean and rigid in its application. Mobile agents in unknown and ubiquitous environments need a flexible security model that accounts for the unique challenges they face. We develop a novel framework to capture principles and trust relationships specific to the mobile agent paradigm. Our framework fills in the shortfall gap in current trust frameworks that attempt to deal with agents and mobility.; Application security models. Initial trust levels between mobile agent principals depend on the application security model. Application designers can provide initial trust conditions to characterize the mobile execution environment; we seed a mobile interaction trust database with these conditions. We defi