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Due to the fast progress of computers and communication networks,
many practical activities and services have been gradually networked to
take advantage of these technologies such as digital cash and electronic
voting services. In these services, users can quickly complete various
transactions no matter when and where they are.
However, a lot of illegal attacks
seriously threaten the security of all communication services in open
network environments. Therefore, to guarantee the quality of these
ever-growing communication services, robust security mechanisms which can
sufficiently protect these systems are urgently desired. Unfortunately,
almost all proposed mechanisms need a lot of arithmetical
computations for users
to ensure the security. These time-consuming computations make the services
inefficient and, especially, unsuitable for the situations where computation
capacities of users are limited such as mobile clients and smart-card users.
Hence, whether these advanced communication services can be widely
accepted or not strongly depends on whether their security and efficiency
issues can be resolved at the same time.
To achieve both security and efficiency, in the first part of this
dissertation we develop a user efficient blind signature scheme for digital
cash and electronic voting services. By adopting the proposed scheme, only
several modular multiplications are required for a user to obtain and verify
a digital signature, a digital cash, or an electronic vote.
Compared with the blind
signature schemes presented in the literatures, the computation overheads of
users are greatly reduced by nearly 99\% in our scheme. Furthermore, the
proposed method not only copes with the unlimited growth problem of the
network banks'' databases but also resolves the possible misuse problem of
the unlinkability property such as to launder money or to safely get a
ransom. In addition, different payment mechanisms are needed for different
types of transactions. In the second part of the dissertation we design
several advanced digital cash services such as information attachable
digital cash, divisible electronic cash, and anonymous rewarding services.
By using these techniques, clients can obtain efficient and diversified
financial services from the servers. Finally, in the third part of the
dissertation we first study the theoretical aspects of
electronic voting schemes,
for example, we show that it is impossible for a collision-free
single-authority
electronic voting scheme to possess both voter uncoercibility and authority
uncoercibility. Since it is easier to buy votes in an electronic election,
we propose a receipt free electronic voting scheme to prevent
dishonest parties from buying votes during elections. In addition, we design
a multi-recastable voting service which makes it possible for a voter to
participate in a sequence of different designated votings by using only one
ticket.
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