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To protect mobile agents from attacks by their execution
environments, or hosts, one class of protection mechanisms uses
"reference states" to detect modification attacks.
Reference states are agent states that have been produced by
non-attacking, or reference hosts. This paper examines this class of
mechanisms and present the bandwidth of the achieved protection.
First, a new general definition of attacks against mobile agents is
presented. As this general definition does not lead to a practicable
protection scheme, the notion of reference states is introduced.
This notion allows to define a protection scheme that can be used to
practically realize a whole number of mechanisms to protect mobile
agents. Therefore, after an initial analysis of already existing
approaches, the abstract features of these approaches are extracted.
A discussion examines the strengths and weaknesses of the general
protection scheme, and a framework is presented that allows an agent
programmer to choose a level of protection using the reference
states scheme. An example illustrates the usage of the framework,
measurements present the overhead of the framework for the case of
the example mechanism.
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