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The concrete tripartite concurrent signature scheme designed by Susilo et al. is found being unambiguity. In other words, any fourth party can identify who is the real signer of the publicly available valid signatures before the keystone is released. In order to overcome this flaw, we proposed an improved concrete tripartite concurrent signature (iCTCS) scheme based on the ring signature. Every user...
In CIS2008, Gao et al. suggested an abuse-free optimistic fair exchange protocol based on the short signature. Their scheme is very efficient in terms of communication. In this paper, we point out that their scheme has two weaknesses. These weaknesses may lead to an unfair situation that Bob may obtain Alice's signature, but Alice can not obtain Bob's signature. In order to overcome these weaknesses,...
In ESS2008, Yang et al. suggested a key-exposure-free chameleon hashing scheme, and it can be used to design signature and some other cryptography mechanism. In this paper, we construct a new timeliness optimistic fair exchange protocol based on this key-exposure-free chameleon hashing scheme. The new scheme does not require the use of interactive zero-knowledge proofs in the exchange phase. In our...
To overcome the secure weakness of the existing proxy blind signature scheme based on ECDLP, an improved scheme is presented. The security of the improved scheme is enhanced by improving on the generate form of the proxy commission and the proxy private key in the proxy phase, the procedure of blinding and unblinding, and the corresponding verification equation of proxy blind signature. The analysis...
Anonymity is an important cryptographical tool to protect user's privacy and identity. In a general ring signature scheme, a member of the ring anonymously produces a signature ?? on a message, where the actual identity of the signer is unknown and the signed message is known for a verifier. However, in some cases, to protect the signer's benefit, we do not hope that a verifier know which message...
Since the concept of proxy signature was introduced in 1996, many variants of proxy signature schemes have been proposed. Among of them, the requirement of proxy signer's privacy protection and the revocation of proxy signer's anonymous identity are needful in some practical applications. Recently, Hu et.al gave a new type of proxy ring signature scheme with revocable anonymity, it allows the original...
A verifiable committed signature is constructed based on Fischlin's signature scheme and is proved of its security in the standard complexity model. And then, an optimistic fair exchange protocol with punishment function is designed based on the committed signature. It will punish the misbehavior of either party in order to ensure the fairness of the exchange. Through the analysis, not only are some...
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