(Georgia Institute of Technology, 2005)
Subbiah, Arun; Blough, Douglas M.
Threshold secret sharing schemes encode data into several shares such that a threshold number of shares can be used to recover the data. Such schemes provide confidentiality of stored data without using encryption, thus avoiding the problems associated with key management. To provide long-term confidentiality, proactive secret sharing techniques can be used, where shares are refreshed or renewed periodically so that an adversary who obtains fewer than the threshold shares in each time period does not learn any information on the encoded data. Share renewal is an expensive process, in terms of the computation and network communication involved. In the proactive model, this share renewal process must complete as soon as possible so that an adversary who compromises servers in the present time period does not learn shares stored in the last time period.
This paper proposes an algorithm where the shares of all the stored data are renewed by the share renewal of only one secret. The computation and network communication overheads are thus drastically reduced, allowing for the share renewal of all the stored data to complete quickly. These benefits are gained at the expense of some performance penalty during reads and writes, which is shown to be worthwhile.
(Georgia Institute of Technology, 2005)
Subbiah, Arun; Blough, Douglas M.
We describe a novel approach for building a secure and fault tolerant data storage service in collaborative work environments. In such environments, sensitive data must be accessible only to a select group of people, whose membership may change over time. Key management issues are a recognized problem in such environments. We eliminate this problem for confidential and secure data storage by using perfect secret sharing techniques for storing data. Perfect secret sharing schemes have found little use in managing generic data because of the high computation overheads incurred by existing schemes. Our proposed approach uses a novel combination of XOR secret sharing and replication mechanisms, which drastically reduce the computation overheads and achieve speeds comparable to standard encryption schemes. The combination of secret sharing and replication manifests itself as an architectural framework, which has the attractive property that its dimension can be varied to tradeoff amongst different performance metrics. We evaluate the properties and performance of the proposed framework to show that the combination of perfect secret sharing and replication can be used to build efficient fault-tolerant and secure distributed data storage systems for collaborative work environments.
(Georgia Institute of Technology, 2004-04-01)
Subbiah, Arun; Ahamad, Mustaque; Blough, Douglas M.
This paper addresses the problem of using proactive cryptosystems for generic data storage and retrieval. Proactive cryptosystems provide high security and confidentiality guarantees for stored data, and are capable of withstanding attacks that may compromise all the servers in the system over time. However, proactive cryptosystems are unsuitable for generic data storage uses for two reasons. First, proactive cryptosystems are usually used to store keys, which are rarely updated. On the other hand, generic data could be actively written and read. The system must therefore be highly available for both write and read operations. Second, existing share renewal protocols (the critical element to achieve proactive security) are expensive in terms of computation and communication overheads, and are time consuming operations. Since generic data will be voluminous, the share renewal process will consume substantial system resources and cause a significant amount of system downtime. Two schemes are proposed that combine Byzantine quorum systems and proactive secret sharing techniques to provide high availability and security guarantees for stored data, while reducing the overhead incurred during the share renewal process. Several performance metrics that can be used to evaluate proactively-secure generic data storage schemes are identified. The proposed schemes are thus shown to render proactive systems suitable for confidential generic data storage.