Cloud-assisted environments are now vital platforms that enable scalable data storage, seamless access, and real-time sharing of data among users. However, using a public cloud storage system to store and share sensitive data leads to security and privacy issues. In order to minimize data maintenance expenses and facilitate secure data sharing, data owners upload encrypted data to a cloud server. Ciphertext-Policy Attribute-Based Encryption (CP-ABE) is an effective technology for enforcing fine-grained access control over shared data. But its computational demands make it challenging to implement directly in resource-limited devices, rendering it less suitable for cloud-assisted environments. To address this problem, we propose a proxy re-encryption scheme that converts an identity-based encryption ciphertext into a CP-ABE ciphertext to establish a fine-grained data sharing mechanism in the cloud-assisted environments. Our scheme provides non-interactive re-encryption capabilities with online-offline re-encryption key generation mechanism while simultaneously accomplishing verifiable outsourced decryption by preserving data confidentiality against the semi-trusted proxy server and unauthorized users. Security assessments and performance evaluations indicate that our proposed scheme accomplishes robust security properties with enhanced computational efficiency compared to existing methods and can be deployed in real-life applications.