Received: 29 June 2020 Revised: 14 April 2021 Accepted: 19 April 2021 DOI: 10.1002/cpe.6377 RESEARCH ARTICLE Modified SeDaSc system for efficient data sharing in the cloud Marwa F. Areed 1 Mohamed M. Rashed 2 Nehal Fayez 2 Ehab H. Abdelhay 2 1 Department of Electrical Engineering, Faculty of Engineering, Damietta University, Damietta, Egypt 2 Department of Electronics and Communications-Faculty of Engineering, Mansoura University, Mansoura, Egypt Correspondence Mohamed Rashed, Department of Electronics and Communications-Faculty of Engineering, Mansoura University, Mansoura, Egypt. Email: memoarashed@gmail.com Summary Organizations tend to store their sensitive data on trusted cloud data storage server to protect it from outside security attacks. However, storing data on the cloud has seri- ous security issues like data misuse from the cloud vendors themselves and attacks from outsources. In this manner, the organizations tend to encrypt their data before storing it in the cloud to protect against the misuse from the cloud vendors and other outer attacks. This article offers an enhancement to Secure Data Sharing in the Cloud (SeDaSc) system in terms of enhancing security metrics related to data privacy and disk storage handling. In the proposed system, the cryptographic server (CS) has been treated a semi-trusted entity by not giving direct access to the data directly. The data encryption is carried at the client side. While, the keys generation and other related cryptographic operations as the access control list (ACL) management are carried at the CS. The client generates the hash of the file needed to be shared in the cloud and then sends such hash to the CS. Then, the CS uses the hash to generate the crypto- graphic key and sends it to the client for encryption process. Further, the proposed system achieves better disk management by only updating the ACL in case of uploading the same file more than once. The CS stores generated key hash and whenever receives a new file, the CS compares the hash of the generated key with other stored hashes. The hash computation in key generation in the proposed system makes the key gen- eration process varies with data size in compare with the key generation process in SeDaSc that is independent on data size. Furthermore, in the case of identical hashes, the ACL will only be updated. Therefore, the identical files neither will be encrypted nor uploaded to cloud twice. The proposed system has been represented mathemati- cally and graphically using high level petri net model and simulated by python language environment. KEYWORDS cloud computing, cloud storage, deduplication, SeDaSc, secure cloud group sharing 1 INTRODUCTION Cloud storage service recently becomes one of the important services of cloud industry. Since it provides organization with on-demand access and flexibility for their data storage service in low cost and geographical independent services. 1-3 Based on recent reports published by Cisco, that by 2021, 94% of workloads and compute instances will be processed by cloud data centers; 6% will be processed by traditional data centers. 4 Cloud storage solves many problems to the small and medium organizations who do not have the sufficient budget to own a private storage server and taking care of securing their sensitive data in this server. 2,5 However, storing data in the cloud means that the users delegate their control Concurrency Computat Pract Exper. 2021;33:e6377. wileyonlinelibrary.com/journal/cpe © 2021 John Wiley & Sons, Ltd. 1 of 10 https://doi.org/10.1002/cpe.6377