The research on electronic voting is a very topic for the progress of democracy. If a secure and convenient electronic voting system is provided, it will be used more frequently to collect people``s opinion for a variety of political and social decisions through cyber space. There has been strong interest in Internet voting to make voting to make voting more convenient. As part of the researches, we propose, in this thesis, efficient and secure Internet voting protocol and threshold blind signature applicable to electronic voting.
We have designed an Internet voting system applicable for worldwide voting which is based on Ohkubo $\emph{et. al.}$``s scheme [32] combined with Public Key Infrastructure (PKI). In our system, voter``s privacy is guaranteed by using blind signature and mix-net, and robustness is provided through the threshold encryption scheme. By employing Java technology, we propose a way of typical implementation for internet voting system. Furthermore, PKI permits worldwide key distribution and achieve "one certificate/one vote" policy. Therefore, anyone can participate in the voting if he gets certificate from Certificate Authority (CA).
Moreover, we proposed an efficient and provably secure threshold blind signature scheme based on Okamoto-Schnorr``s blind signature scheme, which can be used for blind signature-based voting systems with multiple administrators. In our scheme, any $\emph{t}$ out of $\emph{n} signers can generate a blind signature and any one can verify the signature using the same verification process of Okamoto-Schnorr scheme. We prove that our scheme is as secure as Okamoto-Schnorr``s blind signature scheme, and show that our scheme is more efficient than [25].