CERTIFICATELESS SIGNATURE AND BLIND SIGNATURE

Certificateless public key cryptography is a new paradigm introduced by Al-Riyami and Paterson.It eliminates the need of the certificates in traditional public key cryptosystems and the key escrow problem in IDentity-based Public Key Cryptography(ID-PKC).Due to the advantages of the certificateless public key cryptography,a new efficient certificateless pairing-based signature scheme is presented,which has some advantages over previous constructions in computational cost.Based on this new signature scheme,a certificateless blind signature scheme is proposed.The security of our schemes is proven based on the hardness of computational Diffie-Hellman problem.

Tracing Precept against Self-Protective Tortious Decoder

Traceability precept is a broadcast encryption technique that content suppliers can trace malicious authorized users who leak the decryption key to an unauthorized user. To protect the data from eavesdropping, the content supplier encrypts the data and broadcast the cryptograph that only its subscribers can decrypt. However, a traitor may clone his decoder and sell the pirate decoders for profits. The traitor can modify the private key and the decryption program inside the pirate decoder to avoid divulging his identity. Furthermore, some traitors may fabricate a new legal private key together that cannot be traced to the creators. So in this paper, a renewed precept is proposed to achieve both revocation at a different level of capacity in each distribution and black-box tracing against self-protective pirate decoders. The rigorous mathematical deduction shows that our algorithm possess security property.

Efficient and Provably-Secure Certificateless Proxy Re-encryption Scheme for Secure Cloud Data Sharing

In current cloud computing system, large amounts of sensitive data are shared to other cloud users. To keep these data confidentiality, data owners should encrypt their data before outsourcing. We choose proxy reencryption （PRE） as the cloud data encryption technique. In a PRE system, a semi-trusted proxy can transform a ciphertext under one public key into a ciphertext of the same message under another public key, but the proxy cannot gain any information about the message. In this paper, we propose a certificateless PRE （CL-PRE） scheme without pairings. The security of the proposed scheme can be proved to be equivalent to the computational Dire- Hellman （CDH） problem in the random oracle model. Compared with other existing CL-PRE schemes, our scheme requires less computation cost and is significantly more efficient. The new scheme does not need the public key certificates to guarantee validity of public keys and solves the key escrow problem in identity-based public key cryptography.

New Constructions of Identity-Based Threshold Decryption

In this paper, based on the verifiable pair and identity-based threshold cryptography, a novel identity-based （ID-based） threshold decryption scheme （IDTDS） is proposed, which is provably secure against adaptive chosen cipbertext attack under the computational bilinear Diffie-Hellman （CBDH） problem assumption in the random oracle. The pubic cheekability of ciphertext in the IDTDS is given by simply creating a signed E1Gamal encryption instead of a noninteractive zero-knowledge proof. Furthermore, we introduce a modified verifiable pairing to ensure all decryption shares are consistent. Our scheme is more efficient in verification than the schemes considered previously.

Constructing pairing-free certificateless public key encryption with keyword search

Searchable public key encryption enables a storage server to retrieve the publicly encrypted data without revealing the original data contents.It offers a perfect cryptographic solution to encrypted data retrieval in encrypted data storage systems.Certificateless cryptography(CLC)is a novel cryptographic primitive that has many merits.It overcomes the key escrow problem in identity-based cryptosystems and the cumbersome certificate problem in conventional public key cryptosystems.Motivated by the appealing features of CLC,three certificateless encryption with keyword search(CLEKS)schemes were presented in the literature.However,all of them were constructed with the costly bilinear pairing and thus are not suitable for the devices that have limited computing resources and battery power.So,it is interesting and worthwhile to design a CLEKS scheme without using bilinear pairing.In this study,we put forward a pairing-free CLEKS scheme that does not exploit bilinear pairing.We strictly prove that the scheme achieves keyword ciphertext indistinguishability against adaptive chosen-keyword attacks under the complexity assumption of the computational Diffie-Hellman problem in the random oracle model.Efficiency comparison and the simulation show that it enjoys better performance than the previous pairing-based CLEKS schemes.In addition,we briefly introduce three extensions of the proposed CLEKS scheme.

Secure Proxy Re-Encryption from CBE to IBE

In this paper, an efficient hybrid proxy re-encryption scheme that allows the transformation of the ciphertexts in a traditional public key cryptosystem into the ciphertexts in an identity-based system is proposed. The scheme is non-interactive, unidirectional and collude ＂safe＂. Furthermore, it is compatible with current IBE （identity-based encryption） deployments. The scheme has chosen ciphertext security in the random oracle model assuming the hardness of the Decisional Bilinear Diffie-Hellman problem.