Delta Encoding Overhead Analysis of Cloud Storage Systems Using ClientSide Encryption With clientside encryption (CSE), a useru0027s data is encrypted before being transferred to a cloud provider. This ensures that only the intended user has access to the information, but complicates effective file synchronization (between different devices and the cloud). Motivated by prior findings that empirically show that the largest performance differences between popular CSE services (CSEs) and nonCSEs typically are related to the implementation of delta encoding solutions to reduce bandwidth usage, in this paper, we evaluate and provide insights into the practical CSErelated delta encoding overheads. First, we use targeted experiments to demonstrate the delta encoding problem associated with CSE and to compare the practical overhead differences associated with three example services implementing delta encoding. Second, we develop an analytic cost model and use it to show that a simple thresholdbased CSE policy can reduce the bandwidth and storage usage seen by the best CSE considered here, that such a policy has a provable worstcase overhead within a factor two of the best nonCSE, and typically performs much better. The results are highly encouraging, and show that it is possible to provide CSE at limited additional overhead compared to nonCSE services.

TrustFS: An SGXEnabled Stackable File System Framework Data confidentiality in cloud services is commonly ensured by encrypting information before uploading it. However, this approach limits the use of contentaware functionalities, such as deduplication and compression. Although this issue has been addressed individually for some of these functionalities, no unified framework for building secure storage systems exists that can leverage such operations over encrypted data. We present TrustFS, a programmable and modular stackable file system framework for implementing secure contentaware storage functionalities over hardwareassisted trusted execution environments. This framework extends the original SafeFS architecture to provide the isolated execution guarantees of Intel SGX. We demonstrate its usability by implementing an SGXenabled stackable file system prototype while a preliminary evaluation shows that it incurs reasonable performance overhead when compared to conventional storage systems. Finally, we highlight open research challenges that must be further pursued in order for TrustFS to be fully adequate for building productionready secure storage solutions.