Research On Attribute-based Encryption And Attribute-based Signature Schemes

With the development of cryptography, attribute-based cryptosystem has attracted much attention in the field of public key cryptography recently. It is an efficient way to address the problem of secure and fine-grained data sharing in access control scenarios, and can provide message privacy and flexibility of access control at the same time. Besides, it is very suitable in solving problems for two unfixed communicating parties in distributed network environment. Attribute-based cryptosystem has a broad prospect of practical application. To be more practical, we should concern about two aspects: The foremost one is about the efficiency. As the attribute-based encryption scheme associates with an access structure, both the description of ciphertext and the decryption algorithm become more complicated. Thus, it is very important and difficult to shorten the size of the ciphertext and reduce the number of pairings computation. The other one is about the compatibility. It is significant to introduce anonymity and revocability into attribute-based cryptosystem. In this thesis, we make an intensive study of the attribute-based cryptosystem, analyzing ciphertext-policy attribute-based encryption schemes with"AND Gate"or"OR Gate"and attribute-based ring signatures. Get the following research results:1. An attribute-based encryption with wildcards (WABE) with constant ciphertext length is proposed for the first time. It obtained full security in the standard model with the dual system encryption concept introduced by Allision B.. At the same time, the number of pairings computation used in the decryption process is also constant.2. Two more efficient attribute-based ring signature schemes are proposed in this paper. Compared with the existing attribute-based ring signature schemes, the size of the signature is shortened by 1/3, and the number of pairings operation for the verification is also decreased by 1/3. They are proved to be selective-attribute unforgeable in the standard model and unconditional anonymous.3. An attribute-based revocable ring signature scheme is proposed for the fist time. The size of the signature and the number of pairings computation are constant, not depending on the number of attributes. The signature scheme can maintain the signer anonymity against full key exposure, and is proved to be unforgeable in the random oracle model.