Aiming at preserving the privacy of Personal Health Record (PHR) in Smart health (S-health), an attribute-based access control scheme with verifiable outsourced decryption and delegation was proposed. Firstly, the Ciphertext-Policy Attribute-Based Encryption (CP-ABE) was used to realize fine-grained access control of PHR. Secondly, the most complicated decryption was outsourced to the cloud server, and the authorized agency was used to verify the correctness of Partial Decryption Ciphertext (PDC) returned by the cloud server. Then, based on the delegation method, the outsourcing decryption and authentication could be delegated to third-party users without revealing privacy by restricted users. Finally, the adaptive security of the proposed scheme was proved under the standard model. The theoretical analysis results show that the decryption of user side only needs to perform one exponential operation, so that the proposed scheme has strong security and practicability.

In order to response the effect of sampling non-uniformity, based on the representative-based classification algorithm, a Leave-One-Out Ensemble Learning Classification Algorithm (LOOELCA) for symbolic data classification was proposed. Firstly, n small training sets were obtained through leave-one-out methods, where n is the initial training set size. Then independent representative-based classifiers were built by using training sets, and the misclassified classifiers and objects were marked out. Finally, the marked classifier and the original classifier formed a committee and the test set objects were classified. If the committee voted the same, the test object was directly labeled with a class label; otherwise, the test object was classified based on the k-Nearest Neighbor (kNN) algorithm and the marked objects. The experimental results on the UCI standard dataset show that the accuracy of LOOELCA improved 0.35-2.76 percentage points on average compared with the Representative-Based Classification through Covering-Based Neighborhood Rough Set (RBC-CBNRS); compared with ID3, J48, Naïve Bayes, OneR and other methods, LOOELCA also has higher classification accuracy.

Concerning the problem that it is hard to construct digital signature scheme in the standard model, a new signature scheme was proposed, based on Chosen Ciphertext Attack (CCA) secure Publicly Verifiable Public Key Encryption (PVPKE). The construction is based on the following facts: public verifiability is required in both signature scheme and PVPKE scheme; signatures in signature scheme can not be malleable, and ciphertexts in CCA secure PVPKE scheme can not also be malleable. To design the scheme, private key in PVPKE scheme was used to sign, and the public key was used to verify. Security proof was also given. Analysis result indicates that the proposed scheme has good application in the mail transfer system.

Concerning the data's confidentiality when being stored in the untrusted cloud storage, a new encryption algorithm based on the Proxy Re-Encryption (PRE) was proposed, and applied in the access control scheme for the cloud storage. The scheme had partial ciphertexts stored in the cloud storage for sharing, and the others sent to users directly. It was proven that the scheme can ensure the confidentiality of the sensitive data stored in the cloud storage under the third untrusted open environment. By contrast, the experimental results show the transmission of ciphertexts can be controlled by the sender. The scheme used the properties of the proxy re-encryption. The number of ciphertexts' operation and storage did not increase linearly with the increase of the users. It decreased the data computation cost, interactive cost, and the space of the data storage effectively. The scheme achieves sharing securely and efficiently when the sensitive data is stored in the cloud.