2,589 research outputs found
Privacy-preserving efficient searchable encryption
Data storage and computation outsourcing to third-party managed data centers,
in environments such as Cloud Computing, is increasingly being adopted
by individuals, organizations, and governments. However, as cloud-based outsourcing
models expand to society-critical data and services, the lack of effective
and independent control over security and privacy conditions in such settings
presents significant challenges.
An interesting solution to these issues is to perform computations on encrypted
data, directly in the outsourcing servers. Such an approach benefits
from not requiring major data transfers and decryptions, increasing performance
and scalability of operations. Searching operations, an important application
case when cloud-backed repositories increase in number and size, are good examples
where security, efficiency, and precision are relevant requisites. Yet existing
proposals for searching encrypted data are still limited from multiple perspectives,
including usability, query expressiveness, and client-side performance and
scalability.
This thesis focuses on the design and evaluation of mechanisms for searching
encrypted data with improved efficiency, scalability, and usability. There are
two particular concerns addressed in the thesis: on one hand, the thesis aims at
supporting multiple media formats, especially text, images, and multimodal data
(i.e. data with multiple media formats simultaneously); on the other hand the
thesis addresses client-side overhead, and how it can be minimized in order to
support client applications executing in both high-performance desktop devices
and resource-constrained mobile devices.
From the research performed to address these issues, three core contributions
were developed and are presented in the thesis: (i) CloudCryptoSearch, a middleware
system for storing and searching text documents with privacy guarantees,
while supporting multiple modes of deployment (user device, local proxy, or computational cloud) and exploring different tradeoffs between security, usability, and performance; (ii) a novel framework for efficiently searching encrypted images
based on IES-CBIR, an Image Encryption Scheme with Content-Based Image
Retrieval properties that we also propose and evaluate; (iii) MIE, a Multimodal
Indexable Encryption distributed middleware that allows storing, sharing, and
searching encrypted multimodal data while minimizing client-side overhead and
supporting both desktop and mobile devices
Foundations, Properties, and Security Applications of Puzzles: A Survey
Cryptographic algorithms have been used not only to create robust ciphertexts
but also to generate cryptograms that, contrary to the classic goal of
cryptography, are meant to be broken. These cryptograms, generally called
puzzles, require the use of a certain amount of resources to be solved, hence
introducing a cost that is often regarded as a time delay---though it could
involve other metrics as well, such as bandwidth. These powerful features have
made puzzles the core of many security protocols, acquiring increasing
importance in the IT security landscape. The concept of a puzzle has
subsequently been extended to other types of schemes that do not use
cryptographic functions, such as CAPTCHAs, which are used to discriminate
humans from machines. Overall, puzzles have experienced a renewed interest with
the advent of Bitcoin, which uses a CPU-intensive puzzle as proof of work. In
this paper, we provide a comprehensive study of the most important puzzle
construction schemes available in the literature, categorizing them according
to several attributes, such as resource type, verification type, and
applications. We have redefined the term puzzle by collecting and integrating
the scattered notions used in different works, to cover all the existing
applications. Moreover, we provide an overview of the possible applications,
identifying key requirements and different design approaches. Finally, we
highlight the features and limitations of each approach, providing a useful
guide for the future development of new puzzle schemes.Comment: This article has been accepted for publication in ACM Computing
Survey
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