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    "The Digital Signature Schemes for Mobile Agents Delegated by Multiple Users"

    Mobile agent systems can realize a promising computing environment for next generations, in particular an infrastructure suitable for electronic commerce.
    Now, let us consider a situation where a group of users travel together and purchase their tickets for an airplane, a hotel, or a theater etc. Furthermore assume that a mobile agent accomplishes the task on behalf of the users. Since the contract for the purchase is concluded with a signature, the mobile agent must digitally sign the contract document.
    Therefore, in this thesis first we discuss the primitive sheme that is simple combination with multi-signature and proxy signature. Next we show that such a primitive scheme has disadvantages from the viewpoint of offline property and efficiency. In order to resolve the problems, we propose a new digital signature scheme. In our scheme, a key for multiple users is generated beforehand and a digital signature for them is created with the key at once. We compare our scheme with the primitive scheme with respect to signature generation cost, signature size, and verification cost and show that our scheme is superior to the primitive scheme.

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