Confidentiality is a major concern for cloud computing users who must ensure that their sensitive data is protected from unauthorized access or exposure, while still allowing for efficient sharing and collaboration among authorized parties. To address this challenge, a variety of encryption and access control techniques have been proposed and deployed, with varying levels of success.One promising approach to ensuring confidentiality in cloud computing is through the use of proxy re-encryption(PRE), which allows for the secure delegation of decryption rights from one party to another without compromising the privacy of the underlying data. PRE offers a number of advantages over traditional encryption techniques, including the ability to support fine-grained access control,efficient key management, and secure collaboration in multi-party environments.This book provides a comprehensive overview of PRE and its applications in cloud computing security. It covers the theoretical foundations of PRE, including its mathematical underpinnings and security properties, as well as practical aspects such as key management, performance optimization, and integration with other security mechanisms.