Informatica

Since threshold proxy signature has been proposed, all threshold proxy signature schemes are based on the discrete logarithm problems in the modular multiplicative group which has an element g with a large prime order. Nowadays this kind of threshold proxy signature schemes become more and more complex and time-consuming for security and specific requirement. In this paper, we propose a (bilinear) pairing-based threshold proxy signature scheme with known signers, analyze its security and check the following properties the proposed scheme has: non-repudiation, unforgeability, identifiability, distinguishability, verifiability, prevention of misuse of proxy signing right, etc. Moreover, we point out that the proposed scheme is of great efficiency by comparing it with Sun’s and Hsu et al.’s scheme.

Electronic commerce (e-commerce) is a relatively new, emerging and constantly changing area of business management and information technology. One of the technological innovations in banking, finance and e-commerce is the electronic cash (e-cash) transfer system. E-cash transfer systems refers to the technological breakthrough that enables us to perform financial transactions electronically. In this paper we propose a secure e-cash transfer system based on the elliptic curve cryptography. In order to protect the honest participants of the e-cash system we use an elliptic curve blind signature scheme and also we need a trusted third party to trace the criminals.

Combinatorial problems serve as an important resource for developing practical public key cryptosystems and several combinatorial cryptosystems have been proposed in the cryptographic community. In this paper, a combinatorial public key cryptosystem is proposed. The security of the proposed cryptosystem is dependent on a combinatorial problem involving matrices. The system features fast encryption and decryption. However, the system also suffers from some drawbacks. The ciphertext expansion is relatively large and the key sizes are somewhat larger than that of RSA. The security of the system is carefully examined by illustrating the computational infeasibilities of some attacks on the system.

A key exchange (or agreement) protocol is designed to allow two entities establishing a session key to encrypt the communication data over an open network. In 1990, Gunther proposed an identity-based key exchange protocol based on the difficulty of computing a discrete logarithm problem. Afterwards, several improved protocols were proposed to reduce the number of communication steps and the communicational cost required by Gunther's protocol. This paper presents an efficient identity-based key exchange protocol based on the difficulty of computing a discrete logarithm problem. As compared with the previously proposed protocols, it has better performance in terms of the computational cost and the communication steps. The proposed key exchange protocol provides implicit key authentication as well as the desired security attributes of an authenticated key exchange protocol.

A generalized group-oriented cryptosystem (GGOC) based on ElGamal cryptosystem was proposed by Yang et al. in 2003. This study shows that if the authorized decryption sets of users are not properly predetermined in Yang et al.'s GGOC, an unauthorized decryption set of users can recover the encrypted message without difficulty. This study also presents an improved protocol to resist such an attack.