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As a special signature, a directed signature is a type of signature with verification ability which is restricted. In a directed signature scheme, a designated verifier can exclusively verify the validity of a signature. If necessary, the designated verifier or the signer can prove the correction of a signature to a third party. Directed signature schemes are suitable for applications such as bill of tax and bill of health. In this paper, an ID-based directed signature scheme without random oracle is proposed by combining ID-based cryptology with Waters signature. We also give the syntax and security notion of ID-based directed signature without random oracle: unforgeability and invisiblity. Finally, we show that the proposed scheme is unforgeable under the computational Diffie-Hellman assumption, and invisible under the Decisional Bilinear Diffie-Hellman assumption. [ABSTRACT FROM AUTHOR]

At PKC 2006, Chevallier-Mames, Paillier, and Pointcheval proposed encryption schemes that are partially homomorphic, either additively or multiplicatively and announced an open research problem: finding a discrete-log-based cryptosystem that would help realize fully additive or multiplicative homomorphism. In this study, we achieve this goal by lifting the message space of the ElGamal scheme from ]> to ]> . We then apply our scheme for constructing a novel protocol for secure data aggregation in Wireless Sensor Networks. [ABSTRACT FROM AUTHOR]

On-line/off-line signature is an important cryptographic tool, it is widely applied to resource-constrained environment. Recently, an ID-based online/offline signature scheme was proposed for authentication in the AODV protocol. Unfortunately, we show that the scheme are insecure in the paper, it is universally forgeable and malleable. And we give a stronger attack which is able to make that any one can produce a forged signature on arbitrary a message in the absence of the private key of a signer and a valid signature of a message. To overcome the attack, an improved scheme is proposed and we show that the improved scheme is provably secure against adaptive chosen message attack in the random oracle model. [ABSTRACT FROM AUTHOR]

Proxy signature is an important delegation technology. In this paper, we proposed a novel proxy signature scheme with multi-warrant by extending proxy signature. This extension is not a trivial extension, it makes that the size of extended proxy signature is approximate one of original proxy signature. And the size of the extended proxy signature is constant and is independent of warrant΄s number. The scheme is proven secure in the standard model and the security of the scheme is related to the Computational Diffie-Hellman Assumption. Comparison with Huang et.al scheme, our scheme has an advantage over Huang et.al΄s scheme in terms of the size of proxy signature. [ABSTRACT FROM AUTHOR]

Public key cryptography is an important tool in our modern information society. Multivariate public key cryptosystem (MPKC) is a type of public key cryptosystem with high efficiency. In this paper, firstly, we propose a basic multivariate public key encryption scheme which is efficient but insecure. Secondly, we use the internally perturbed plus modifier to modify the basic scheme, and get a improved scheme which is secure against known types of attacks. Finally, we provide a practical implementation of the improved scheme. [ABSTRACT FROM AUTHOR]