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With the advent of cloud computing, data privacy has become one of critical security issues and attracted much attention as more and more mobile devices are relying on the services in cloud. To protect data privacy, users usually encrypt their sensitive data before uploading to cloud servers, which renders the data utilization to be difficult. The ciphertext retrieval is able to realize utilization over encrypted data and searchable public key encryption is an effective way in the construction of encrypted data retrieval. However, the previous related works have not paid much attention to the design of ciphertext retrieval schemes that are secure against inside keyword-guessing attacks (KGAs). In this paper, we first construct a new architecture to resist inside KGAs. Moreover we present an efficient ciphertext retrieval instance with a designated tester (dCRKS) based on the architecture. This instance is secure under the inside KGAs. Finally, security analysis and efficiency comparison show that the proposal is effective for the retrieval of encrypted data in cloud computing.

With networking became prevalent, the amount of data to be stored and managed on networked servers rapidly increases. Meanwhile, with the improvement of awareness of data privacy, the user’s sensitive data is usually encrypted before uploading them to the cloud server. The searchable public-key encryption provides an efficient mechanism to achieve data retrieval in encrypted storage. Therefore, it is a critical technique on promoting secure and efficient cloud storage. Unfortunately, only few the existing schemes are secure to resist outside keyword guessing attacks. In this paper, we propose two efficient searchable public-key encryption schemes with a designated tester (dPEKS). One is a basic dPEKS, where the dPEKS ciphertext indistinguishability is proved without the random oracle. Meanwhile, the basic scheme is secure to resist the outside KGA since it satisfies the property of trapdoor indistinguishability. Comparing with the existing dPEKS schemes which use expensive pairing computation, our scheme is more efficient since we only need multi-exponentiation. Another is an enhanced dPEKS scheme. With the sender’s identity is kept secret from server, this scheme can provide stronger security.

With the improvement of awareness of data privacy, the user's sensitive data is usually encrypted before uploading them to the cloud. The searchable public-key encryption with keyword search provides an efficient mechanism to achieve the encrypted data retrieval without the complicated key management of symmetric encryption. Therefore, it is a critical technique on promoting secure and efficient cloud storage. Unfortunately, only one existing construction of ciphertext retrieval scheme is secure against inside keyword guessing attacks (KGA). In this paper, we build a framework to resist insider attacks. Additionally, we propose an efficient ciphertext retrieval with keyword search scheme with a designated tester (dCRKS), which is secure against inside keyword guessing attacks (KGA). Our security proof and performance analysis demonstrate that our scheme is practical for retrieval data stored in the cloud server.

With the improvement of awareness of data privacy, the user's sensitive data are usually encrypted before uploading them to cloud. Searchable encryption is a critical technique on promoting secure and efficient cloud storage. In particular, publickey encryption with keyword search (PEKS) provides an elegant approach to achieve data retrieval in encrypted storage. All existing searchable publickey encryption schemes only provide the security based on classical cryptography hardness assumption. With the development of quantum computers, these schemes will be insecure. Based on the lattice hardness assumptions, we propose a new searchable publickey encryption scheme with a designated tester (dPEKS). Our scheme has advantages: First, our scheme is the first searchable publickey encryption scheme that is considered to be secure even if quantum computers are ever developed. Second, our scheme achieves the trapdoor indistinguishability. The trapdoor indistinguishability implies the security against outside offline keyword guessing attacks (KGAs). Last, our scheme can achieve the trapdoor anonymity for server.

Group signatures allow a group member to sign messages anonymously on behalf of the group. Generally, group signatures have anonymity, traceability and authentication. It has been well applied in practical distributed security communication environments. However, very few schemes can achieve the non-frameability and support dynamic membership management. In this paper, we propose a new group signature scheme. Our scheme achieves the non-frameability without the trusted issuer. Meanwhile, this scheme can support dynamic members join and revocation without incurring other secure threats. Furthermore, in our scheme, the size of group member's private key and the size of group public key are shorter than other schemes while the costs to be kept constant for signing and verifying. In particular, we prove that our scheme achieves anonymity, traceability and non-frameability under the random oracle model.