Sharif Digital Repository

Cloud storage provides an accessible and cheap space for data storage. There is usually no trust between users and the Cloud. Consequently, to maintain confidentiality, outsourcing and storing sensitive data in an encrypted form is necessary. In applications where data sharing between several users is required, ciphertext-policy attribute-based encryption(CP-ABE) has been considered a promising solution, but the lack of efficiency and flexibility limits its usage in applications such as IoT. These problems are usually related to both the underlying structure and the required peripheral processes, such as key revocation. In this thesis, two schemes with the same basic structure and different...