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Group Sharing and Random Access in Cryptographic Storage File Systems

Traditional cryptographic storage uses encryption to ensure confidentiality of file data. However, encryption can prevent efficient random access to file data. Moreover, no cryptographic storage file system allows file sharing with similar semantics to UNIX group sharing. The Cryptographic Storage File System (Cepheus) provides confidentiality and integrity of data while enabling efficient random access and file sharing using mechanisms similar to UNIX groups. Cepheus uses a delayed-write-encryption policy for caching, delayed re-encryption for distributed re-encryption, and a hash tree structure beneath the inode for integrity. While maintaining confidentiality and integrity, the cost of reading a block is O(1) amortized over a sequential read of the entire file of n blocks. Writes execute in worst-case O(logn) time. Thesis Supervisor: Ronald L. Rivest Title: E. S. Webster Professor of Electrical Engineering and Computer Science