Biblio

With the rising popularity of file-sharing services such as Google Drive and Dropbox in the workflows of individuals and corporations alike, the protection of client-outsourced data from unauthorized access or tampering remains a major security concern. Existing cryptographic solutions to this problem typically require server-side support, involve non-trivial key management on the part of users, and suffer from severe re-encryption penalties upon access revocations. This combination of performance overheads and management burdens makes this class of solutions undesirable in situations where performant, platform-agnostic, dynamic sharing of user content is required. We present NEXUS, a stackable filesystem that leverages trusted hardware to provide confidentiality and integrity for user files stored on untrusted platforms. NEXUS is explicitly designed to balance security, portability, and performance: it supports dynamic sharing of protected volumes on any platform exposing a file access API without requiring server-side support, enables the use of fine-grained access control policies to allow for selective sharing, and avoids the key revocation and file re-encryption overheads associated with other cryptographic approaches to access control. This combination of features is made possible by the use of a client-side Intel SGX enclave that is used to protect and share NEXUS volumes, ensuring that cryptographic keys never leave enclave memory and obviating the need to reencrypt files upon revocation of access rights. We implemented a NEXUS prototype that runs on top of the AFS filesystem and show that it incurs ×2 overhead for a variety of common file and database operations.

Users have accumulated years of personal data in cloud storage, creating potential privacy and security risks. This agglomeration includes files retained or shared with others simply out of momentum, rather than intention. We presented 100 online-survey participants with a stratified sample of 10 files currently stored in their own Dropbox or Google Drive accounts. We asked about the origin of each file, whether the participant remembered that file was stored there, and, when applicable, about that file's sharing status. We also recorded participants' preferences moving forward for keeping, deleting, or encrypting those files, as well as adjusting sharing settings. Participants had forgotten that half of the files they saw were in the cloud. Overall, 83% of participants wanted to delete at least one file they saw, while 13% wanted to unshare at least one file. Our combined results suggest directions for retrospective cloud data management.