Digital signatures are one of the main achievements of public-key cryptography and constitute a fundamental tool to ensure data authentication. Although their universal verifiability has the advantage to facilitate their verification by the recipient, this property may have undesirable consequences when dealing with sensitive and private information. Motivated by such considerations, undeniable...

This paper presents a strong designated verifiable signcryption scheme, in which a message is signcrypted by a signcryptor and only a specific receiver, who called a “designated verifier”, verifies it using his own secret key. The scheme is secure, as an adversary can not verify the signature even if the secret key of the signer is compromised or leaked. The security of the proposed scheme lies...

In 2004, Zhang and Xiao proposed a multisignature scheme based on ElGamal discrete logarithm algorithm which allows a signer group to sign a signature and a verifier group to verify the validity of the signed signature. In this paper, we will show that any verifier in the verifier group can break their scheme by replacing the valid signed message with another forged one which will also be authe...

A rich set of proxy signature schemes have been widely researched and discussed so far. However, they have been mainly focusing on dealing with one or two separate proxy situations each. In this article, the authors proposed the generalization of the (t1/n1 − t2/n2) proxy signature scheme based on the factorization of the square root modulo of a composite number. This scheme can be applied to e...

Undeniable signature is an intriguing concept introduced by Chaum and Antwerpen at Crypto’89. In 1999, Lee and Hwang presented two group-oriented undeniable signature schemes with a trusted center. Their schemes are natural generalizations of Chaum’s zero-knowledge undeniable signature scheme proposed in 1990. However, we find that the Lee-Hwang schemes are insecure. In this paper, we demonstra...

Based on ElGamal system, a group-oriented threshold signature and authenticated encryption scheme was put forward. After being signed by a signer group employing ) , ( n t threshold signature scheme, the message m was transmitted to a particular verifier group, and then the signature was verified through the cooperation of k ones from the verifier group with l members. Similarly, a general auth...

Fair exchange signature is of importance in the field of the open-network-based security applications. A new multi-party concurrent signature (MPCS) scheme based on designated verifiers is introduced, which features fairness and unforgeability based on the hardness of the Computational Diffie-Hellman (CDH) assumption in the random oracle model. In this scheme, each signer has the right to choos...

Proxy signature is a signature scheme that an original signer delegates his/her signing capability to a proxy signer, and then the proxy signer creates a signature on behalf of the original signer. In this paper we show various attack scenarios against previous proxy signature schemes, which shows that proxy signature schemes should be designed very carefully. Based on these weaknesses, we prov...

random oracles Bin Wang and Qing Zhao Information Engineering College of Yangzhou University No.196 West HuaYang Road, Yangzhou City, Jiangsu Province, P.R.China E-mail: [email protected] Abstract: Server-aided verification(SAV) signature is useful for power-constrained devices since a powerful server can assist in performing costly operations such as pairing operations. Wu et al. [13] defined t...