In the Outsourced Database (ODB) model, entities outsource their data management needs to a third-party service provider. Such a service provider offers mechanisms for its clients to create, store, update, and access (query) their databases. This work provides mechanisms to ensure data integrity and authenticity for outsourced databases. Specifically, this article provides mechanisms that assure the querier that the query results have not been tampered with and are authentic (with respect to the actual data owner). It investigates both the security and efficiency aspects of the problem and constructs several secure and practical schemes that facilitate the integrity and authenticity of query replies while incurring low computational and communication costs.

Database outsourcing is an important trend which involves data owners farming out their data management needs to an external service provider. One important requirement is to maintain the integrity and authenticity of outsourced data. Whenever an outsourced database is queried, the corresponding query reply must be demonstrably authentic. Furthermore, a reply must include a proof of completeness to convince the querier that no data matching the query predicate(s) has been omitted. In this paper, we suggest new techniques in support of efficient authenticity and completeness guarantees of such query replies.

Peer-to-peer systems enable efficient resource aggregation and are inherently scalable since they do not depend on any centralized authority. However, lack of a centralized authority prompts many security-related challenges. Providing efficient security services in these systems is an active research topic which is receiving much attention in the security research community. In this paper, we explore the use of threshold cryptography in peer-to-peer settings (both Internet- and MANET-based) to provide, in a robust and fault tolerant fashion, security services such as authentication, certificate issuance and access control. Threshold cryptography provides high availability by distributing trust throughout the group and is, therefore, an attractive solution for secure peer-groups. Our work investigates the applicability of threshold cryptography for membership control in peer-to-peer systems. In the process, we discover that one interesting proposed scheme contains an unfortunate (yet serious) flaw. We then present an alternative solution and its performance measurements. More importantly, our preliminary work casts a certain degree of skepticism on the practicality and even viability of using (seemingly attractive) threshold cryptography in certain peer-to-peer settings.