The Overhead of Confidentiality and Client-side Encryption in Cloud Storage Systems

Client-side encryption (CSE) is important to ensure that only the intended users have access to information stored in public cloud services. However, CSE complicates file synchronization methods such as deduplication and delta encoding, important to reduce the large network bandwidth overheads associated with cloud storage services. To investigate the overhead penalty associated with CSE, in this paper, we present a comprehensive overhead analysis that includes empirical experiments using four popular CSE services (CSEs) and four popular non-CSEs. Our results show that existing CSEs are able to implement CSE together with bandwidth saving features such as compression and deduplication with low additional overhead compared to the non-CSEs. The most noticeable differences between CSEs and non-CSEs are instead related to whether they implement delta encoding and how effectively such solutions are implemented. In particular, fewer CSEs than non-CSEs implement delta encoding, and the bandwidth saving differences between the applications that implement delta encoding can be substantial.