| Summary: | 碩士 === 國立臺灣大學 === 電機工程學系研究所 === 86 === Digital signatures resemble handwritten signatures and provide integrity and a
uthenticity for messages travelling over insecure channels. Valid signatures
convince receivers that messages really come from alleged sources and are not
modified during transmission. Sometimes one may expect others could check val
idity of his signatures but have no way to learn his identity. This motivatio
n results in anonymous one-time digital signature schemes. In such a scheme,
a trusted third party, the guarantor, is introduced. Users do not produce sig
nature keys independently but have to cooperate with the guarantor. During ea
ch negotiation between a user and the guarantor,that user's identity is embedd
ed in the signature key. If he uses each of his keys only once, he is anonymo
us. However, if he uses any key to sign two different messages, he will be ca
ught and punished by the guarantor. In this thesis, a secure and efficient a
nonymous one-time signature scheme based on quadratic residues is proposed. E
ach user gets his electronic license from the guarantor and uses it to negotia
te with one to produce his signature keys. Due to the introduction of electro
nic licenses, key generation is quite simple and cheater detection is easy. T
he guarantor's load is greatly reduced. An improved version of this basic sch
eme suggests that keys be generated in batch rather than one by one and furthe
r reduces load of the guarantor.
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