Although outsourcing data to the cloud has many advantages, cloud computing introduces new privacy and security requirements on how data is stored and accessed. To ensure data confidentiality, use of encryption is a common strategy. A problem with this strategy is that for large data it becomes difficult to access and update data, and to ensure data integrity and data provenance without decrypting all the data. The problem becomes severe when it comes to accessing and modifying large files using mobile devices with limited processing and bandwidth capabilities. In this paper, we present CloudEFS, a novel storage framework to efficiently access and update large encrypted data. A new cached hash algorithm enables efficient updates of data integrity and provenance information. CloudEFS provides improved privacy by hiding not only content but also metadata such as data size, file count, file structure and file history.
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