Henrique Domingos

A case study on event dissemination in an active overlay network environment

In this paper, we describe a case study of the design and development of a group-conferencing tool suite, built on top of an overlay network based event dissemination framework, which is extensible via quality of service template plug-ins. We explain, for each of the tools, how the framework built-in conveniences were explored to create simple but effective distributed solutions, backed by the appropriate quality of service templates, whose design we also discuss.

Practical Privacy-Preserving Content-Based Retrieval in Cloud Image Repositories

Storage requirements for visual data have been increasing in recent years, following the emergence of many highly interactive multimedia services and applications for mobile devices in both personal and corporate scenarios. This has been a key driving factor for the adoption of cloud-based data outsourcing solutions. However, outsourcing data storage to the Cloud also leads to new security challenges that must be carefully addressed, especially regarding privacy. In this paper we propose a secure framework for outsourced privacy-preserving storage and retrieval in large shared image repositories. Our proposal is based on IES-CBIR, a novel Image Encryption Scheme that exhibits Content-Based Image Retrieval properties. The framework enables both encrypted storage and searching using Content-Based Image Retrieval queries while preserving privacy against honest-but-curious cloud administrators. We have built a prototype of the proposed framework, formally analyzed and proven its security properties, and experimentally evaluated its performance and retrieval precision. Our results show that IES-CBIR is provably secure, allows more efficient operations than existing proposals, both in terms of time and space complexity, and paves the way for new practical application scenarios.

Management and search of private data on storage clouds

The article presents a solution for storage and management of private data kept in Internet Storage Clouds. The solution supports operations over the data kept ciphered, including reads, writes and searches based on multiple keywords and relevance classification. The approach is based on a middleware architecture supported by homomorphic encryption techniques combined with dynamic indexing mechanisms. The solution preserves conditions of privacy without need to either decipher data during operations in the cloud or transfer the data during searches. The article further describes an implementation prototype of the solution and its evaluation. The performance obtained in different implementation scenarios is analyzed and compared to a solution promoted by AMAZON S3. The evaluation shows that the solution is viable, offers more security and control for the user and does not aggravate conditions of latency and data availability.

Multimodal Indexable Encryption for Mobile Cloud-Based Applications

In this paper we propose MIE, a Multimodal Indexable Encryption framework that for the first time allows mobile applications to securely outsource the storage and search of their multimodal data (i.e. data containing multiple media formats) to public clouds with privacy guarantees. MIE is designed as a distributed framework architecture, leveraging on shared cloud repositories that can be accessed simultaneously by multiple users. At its core MIE relies on Distance Preserving Encodings (DPE), a novel family of encoding algorithms with cryptographic properties that we also propose. By applying DPE to multimodal data features, MIE enables high-cost clustering and indexing operations to be handled by cloud servers in a privacy-preserving way. Experiments show that MIE achieves better performance and scalability when compared with the state of art, with measurable impact on mobile resources and battery life.

Towards an Image Encryption Scheme with Content-Based Image Retrieval Properties

In this paper we introduce a new secure cryptographic scheme, named IES-CBIR, specifically designed for images and their outsourced storage and retrieval in large private image repositories. Our solution enables both encrypted storage and querying using Content Based Image Retrieval (CBIR), while preserving privacy. We have implemented a prototype system around the proposed scheme, and experimentally analyzed its performance when compared to similar proposals for privacy-preserving image retrieval. Our results show that IES-CBIR allows more efficient operations than existing proposals, both in terms of time and space overheads, while enabling less restrictive application scenarios.

TMS: a trusted mail repository service using public storage clouds

In this paper we present the Trusted Mail System (TMS), a dependable Email repository service that explores multiple untrusted storage clouds for storing, accessing and searching private email data. The system architecture provides security and reliability services while leveraging the heterogeneity and diversity offered by different untrusted cloud storage solutions from different service providers. To address dependability issues, TMS enforces a security model that protects confidentiality and integrity of mailboxes stored in those clouds, adding availability, reliability and intrusion-tolerance guarantees. The system uses homomorphic encryption mechanisms and indexing techniques allowing ranked multi-keyword searching operations over encrypted email messages and its contents. We illustrate TMS feasibility from an implemented prototype, evaluating its performance, design options, and services. The experimental results show that the solution is viable, offers reliability and privacy control for the users and does not aggravate conditions of data-access latency and availability.

Topic 15 peer-to-peer and web computing

Distributed systems have experienced a shift of scale in the past few years. This evolution has generated an interest in peer-to-peer systems and resulted in much interesting work. Peer-to-peer systems are characterized by their potential to scale due to their fully decentralized nature. They are self-organizing, adapting automatically to peer arrivals and departures, and are highly resilient to failures. They rely on a symmetric communication model where peers act both as servers and clients. As the peer-to-peer concepts and technologies become more mature, many distributed services and applications relying on this model are envisaged in the context of large-scale distributed and parallel systems. This topic examines peer-to-peer technologies, applications, and systems, and also identifies key research issues and challenges. Twenty papers were submitted to this topic and six were accepted. These papers were organized in two sessions. The first one has three papers discussing peer-to-peer overlay construction, and the second session is devoted to applications of peer-to-peer overlays. In “Epidemic-style management of semantic overlays for content-based searching”, the authors presents a proactive epidemic protocol to build semantic overlays and cluster peers having similar content. In “Long range contacts in overlay networks”, the authors propose a protocol to reactively add long range contacts in an overlay network based only on actual routing requests. The approach enables to tolerate non uniform distribution of the peers in the logical space. In the paper “Combining the use of clustering and scale-free nature of user exchanges into a simple and efficient P2P system”, the results of a depth-first search are used to create links between peers so that resulting neighbours in the overlay are peers which have successfully cooperated to find results for previous searches. “AGNO: an adaptive group communication scheme for unstructured P2P networks” presents a group notification protocol which operates on an unstructured peer-to-peer network. In this approach, the results of previous lookups operations are also used to speed up the notification process. In “Pastis: a highly-scalable multi-user peer to peer file system”, the authors present the design and evaluation of a read-write peer-to-peer file sharing system based on the Pastry/Past approach. The last paper, entitled “Semantic peer to peer overlays for publish/subscribe networks”, presents a content-based publish-subscribe system. A peer-to-peer overlay is built so that peers get connected to neighbours having similar subscribing patterns.