Controllable Predicate Encryption Schemes for Privacy Preserving Search in Cloud Storage

• Main Authors: Shi-Yuan Huang, 黃士原
• Other Authors: Chun-I Fan
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/69505113963058303313

博士 === 國立中山大學 === 資訊工程學系研究所 === 101 === In traditional public-key encryption, a receiver generates a pair of keys, a private key SK and a corresponding public key PK. A sender obtains the above public key and encrypts a message with this key. Only the owner of SK, the receiver, can decrypt the ciphertext and read the message. The above scenario only suits point-to-point communication. Recently, cloud computing prevails over the whole world, and a lot of sensitive data will be stored into the cloud. Due to the data privacy, it is necessary for users to encrypt their sensitive data before storing them into the cloud. However, there exist some shortcomings in the setting of traditional public-key encryption. When the receiver wants to search some particular data that are stored in the cloud server, the server cannot perform search over the ciphertext space. In order to solve this problem, predicate encryption schemes were proposed. Predicate encryption is a new cryptographic primitive that provides fine-grained control over the accesses to encrypted data. In the setting of predicate encryption, any message can be encrypted with PK and a set of attributes. The receiver can make use of SK to generate a search token corresponding to a predicate. The cloud server can take this token generated by the receiver to test or decrypt the ciphertexts if and only if the set of attributes of the ciphertexts satisfies the predicate of the secret token. In this dissertation, we propose a controllable predicate encryption scheme for inner product predicates, which is the first work that can provide timed-release services and data self-destruction property. Owing to these properties, the sender can set the readable/unreadable time of the files to be sent to the receiver. The receiver can read the sent file only after the readable time. After the unreadable time, the structure of the file will be destroyed and the file will become unreadable. Furthermore, for practical usage purposes, an extended scheme, which is based on the proposed scheme, provides not only timed-release services and data self-destruction but also long message encryption and search without decryption. In the extended scheme, the length of encrypted messages does not depend on the order of the group. Moreover, the cloud server can obtain only the matched ciphertexts after the search. In order to improve efficiency of predicate encryption, we construct a lightweight scheme of the predicate encryption that uses hidden vector predicates rather than inner product predicates. We also present a lightweight symmetric scheme of the predicate encryption, which provides two privacy preserving search functionalities, including revocable delegated search and delegated search without decryption. Due to these functionalities, the owner of a cloud storage can easily control the lifetimes and search privileges of cloud data. We also present system implementations of the above lightweight schemes in the Appendixes.