POTSHARDS: Secure Long-Term Archival Storage Without Encryption
Mark W. Storer, Kevin M. Greenan, Ethan L. Miller · 2006
Modern archival storage systems either store data in the clear, ignoring security, or rely on keyed encryption to ensure privacy. However, the use of encryption is a major concern when data must be stored an indefinite period of time—key management becomes increasingly difficult as file lifetimes increase, and data loss becomes increasingly likely because keys are a single point of failure and losing a key is comparable to data deletion. Moreover, traditional systems are subject to the obsolescence of encryption algorithms themselves, which can expose petabytes of data the instant a cryptographic algorithm is broken. To address these concerns, we developed POT-SHARDS, an archival storage system that addresses the long-term security needs of data with very long lifetimes without the use of encryption. POTSHARDS separates security and redundancy by utilizing two levels of secret splitting in a way that allows the original data to be reconstructed from the stored pieces. However, the data structures used in POTSHARDS are also designed in such a way that an unauthorized user attempting to collect sufficient shares to reconstruct any data will not go unnoticed because it is very difficult to launch a targeted attack on the system, even with unrestricted access to a few archives. Since POTSHARDS provides secure storage for arbitrarily long periods of time, its data structures include built-in support for consistency checking and data migration. An evaluation of our POTSHARDS implementation shows that it stores and retrieves data at 2.5–5 MB/s, demonstrates its ability to recover user data given all of the pieces a user has stored across the archives, and shows its ability to recover from the loss of an entire archive.