The Design And Analysis Of Ring Digital Signatures

Ring digital signature is a new kind of anonymous signature which can provide unconditional anonymity of the signer. The signer can choose some other users to form a ring that includes the signer and sign messages on behalf of the ring without revealing any information about the identity of the signer. This paper researches on ring signatures thoroughly and the main constributions are as follows.Firstly, ID-based ring signatures are discussed and two measures are proposed to solve the problem that a trustfed third party is needed in ID-based ring signatures. This paper proposes two new ID-based ring signature schemes using bilinear pairing and multilinear pairing respectively and proves that the later one is secure against adaptive chosen message and identity attack in the random oracle model.Then existing proxy ring signature schemes are analysed. All of those schemes only provide the anonymity of the proxy signer while keep the identity of the original signer known to others. A new proxy ring signature which can provide the anonymity of both the original signer and the proxy signer is proposed.After that linkable ring signatures are studied and a new scheme with strong separability is proposed on the difficulty of discrete logarithm and factoring of big composite number, which allows the use of both DL-based and ID-based public keys at the same time. And the participants can choose public key systems, system parameters and keys independently of each other. So it is more practical.Finally, this paper introduces forward security into ring signature and proposes two ring signature schemes with forward security on the difficulty of quadratic root modulo composite number. Even the attacker obtains the current secret key of some user illegally, he still can not forge the signature of the past time period.