| Summary: | 碩士 === 大葉大學 === 資訊工程研究所 === 90 === The focuses of the research contain two parts: one is the digital signature, and the other is the proxy digital signature. For the part of digital signature, the current related schemes are established under the public-key cryptosystem, in which each signer is provided with a secret key and a public key. From the view of security, such a kind of construct for a scheme is insufficient for the weak protection of the secret key. Therefore, a new scheme is proposed to provide each signer with two secret keys and one public key for the operation of digital signature. Unless an attacker can force to derive these two secret keys at the same time, he disables to invade the cryptosystem only by one secret key so the security of the scheme still can be guaranteed. The proposed scheme can be applied to the present related schemes for the digital signature and succeeds in the promotion of both security and efficiency in performance.
As to the part of proxy digital signature, a secure manner is required for the communication between the original and the proxy signers to deliver the delegation parameters for the purpose of delegation proxy in the previous proxy digital signature schemes. Aim at the avoidance of the secure manner, an interactive communication of proxy digital signature scheme is proposed by Zhang. The so-called interactive communication means the to and fro exchange of the parameters between the original and the proxy signers. Such a kind of delegation obviously consumes with the bandwidth and becomes inefficient. Thus, a new proxy digital signature scheme different from that by Zhang is proposed to achieve the purpose of delegation proxy without a secure manner.
In the recent years, the elliptic curve cryptosystem (ECC) is widely approved of the application in both security and efficiency for the design of the crypto-scheme. Its potential future for various applications inclines the elliptic curve cryptosystem to replace the current RSA or DSS cryptosystem in some specific condition. Consequently, there develops a new tendency to the related research. Using a shorter private key than that of the RSA or DSA, the ECC can achieve the equal level of security under a lower computational overheads (how much computation is required to perform the public key and private key transformations) and key size (how many bits are required to store the key pairs and any system parameters). Generally speaking, when the length of q reaches 160-bit in the ECC over q-bit domain, whose security is equivalent to the 1024-bit modulus in the RSA. A shorter private key means the shorter bandwidth required and storage space. For the application of computer science, such a characteristic is a critical key to develop the network.
Owing to the superiority, the research is put into the ECC to construct a new digital signature cryptosystem with higher efficiency than the traditional ones.
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