Research On Multi-User Oriented Certificateless Digital Signature Schemes

As an important research component of public key cryptography, digital signature scheme could be used to in the process of data transmission to achieve authentication of an identity, integrity of data and non-reputation. The identity-based signature (IBS) schemes take user’s unique identifier as the public key, and simplify the problem of key management that is a heavy burden in certificate-based signature (CBS) scheme. However, IBS schemes bring the key escrow problem for the reason that private keys are issued by KGC which can forge any user’s signature. Since Al-Riyami and Paterson proposed the concept of certificateless cryptography(CLC), CLC has been extensively developed. In constrast to CBS, certificateless signature(CLS) does not suffer from the key management problem for no binding the identity of user with its public-key. Moreover, the private key is composed by two parties:one is the partial private key generated by PKG, the other one is the secret value chosen by the user itself. CLS solves the key escrow problem for that KGC can not get user’s secret value.There are several certificateless signature schemes have been proposed. However, the traditional digital signature scheme with single user cannot meet the security needs of new application environment with multi-user, such as VANETs(vehicle ad hoc networks) and Cloud Platform and so on. In this paper, we study multi-user oriented certificateless digital signature schemes, including certificateless multi-signature scheme, certificateless ring signature scheme, certificateless proxy signature scheme and certificateless aggregate signature scheme. From the security analysis of the existing scheme, the dissertation investigates the multi-user oriented certificateless signature scheme, and takes designing schemes, analyzing the security and efficiency as the main research content. The major research results of this dissertation are as follows:1. Proposes a certificateless sequential multi-signature scheme. There are some problems in the existing certificateless multi-signature schemes, for no formal security proof, or scheme itself exists security flaws, or the linear relationship between the signature and the user number. In this dissertation, we first analyze the security of a certificatelss sequential multi-signature scheme. Then, by using bilinear pairings, we proposed a certificateless sequential multi-signature scheme which take lower computation cost and communication cost for only generating one signature message and using less bilinear pairings. Finally, we prove that this scheme can resist the forgery attack under the random oracle model.2. Proposes a certificateless ring signature scheme. Using the difficulty of large number factorization, we construct a certificateless ring signature scheme. In the algorithm of PartialKeyGen, the scheme introduces the interaction between the KGC and the signer and makes the Partial Private Key contain the user’s choice of secret information, it can prevent malicious attack of KGC. Scheme uses the RSA technology, without complex bilinear pairings operations, therefore is efficient. Finally, we prove that this scheme is equivalent to the RSA problem in the random oracle model.3. Analyzes the security of Chen-Liu certificateless proxy signature scheme. Chen et al. claimed that their scheme was existentially unforgeable under the chosen message attack in the model of random oracle. Unfortunately, we will show that Chen-Liu certificateless proxy signature scheme is insecure by giving two concrete attacks. That is, a malicious original signer can forge a valid proxy signatures and a malicious proxy signer can create a valid proxy signature that is beyond the delegation of the original signer.4. Proposes a certificateless aggregate signature scheme. In this dissertation, we first analyze the security of a certificatelss aggregate signature scheme. Then, by using bilinear pairings, we propose a certificateless aggregate signature scheme which take lower computation cost and communication cost using less bilinear pairings. Finally, we prove that this scheme is equivalent to the CDH problem in the random oracle model.