1,720,971 research outputs found
Practical privacy-preserving cryptographic protocols
No full textThe main aim of this thesis is to construct efficient protocols to help preserve privacy of users in today's digital world. We are interested in not only theoretically sound constructions but also those which could be deployed in practice. In particular, we are interested in constructions whose security could be based on standard assumptions rather than idealized ones which are hard to realize in real life. We look at different types of protocols which include: proof systems, blind signatures, group signatures and their applications. We investigate the security of such schemes and present new efficient constructions. We investigate the Groth-Sahai proof system and extend its applicability to new settings which were not possible before. We then provide some efficient implementations of different proof systems in different models and compare and contrast their efficiency. For such implementations, we present optimization techniques which make the proofs more efficient and hence more suitable for being deployed in practice. For instance, we provide details of how to efficiently batch verify such proofs which would significantly speed up the verification process. In particular, we look at the case of using proof systems for the problem of circuit satisfiability. We also look at another application of proof systems and consider the case of proving set membership with as little interaction as possible. We then turn our attention to different variants of signature schemes where we present a new efficient blind signature scheme whose security is proved under standard assumptions. We also look at group signatures and related primitives where we formally investigate the security of group blind signatures for which we present a formalized security model for the first time. This would promote more rigorous security proofs. We then present an efficient construction which has a number of desirable properties and yet its security does not rely on any non-standard assumptions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Subset Signatures with Controlled Context-Hiding
No full textSubset signatures are a variant of malleable signatures which allow anyone to derive signatures on any subset of previously signed sets in such a way that derived signatures are indistinguishable from new signatures on the subset (i.e.~context-hiding). Such a primitive has many applications. In some scenarios, it might be desirable to restrict some elements in the set from preserving the context-hiding property. In other words, it might be desirable to allow the signer, at the time of the signing, to mark specific elements (which we refer to hereafter as the \emph{restricted subset}) such that the inclusion of any elements from the restricted subset in any derived signatures would violate the context-hiding property and make the derived signature linkable to the original signature. In this paper, we put forward the notion of subset signatures with controlled context-hiding. We propose a security model and a generic construction as well as efficient instantiations which do not rely on random oracles. Our instantiations are structure-preserving and therefore could be useful for other applications.As a special case of our constructions when the restricted subset is empty, we obtain more efficient constructions of standard subset signatures. Our constructions, which satisfy the strongest existing security definitions, have constant-size keys and outperform existing constructions in every respect. As part of our contribution, we construct a structure-preserving signature scheme with combined unforgeability that signs a vector of group elements while maintaining constant-size signatures. The scheme has some desirable properties and combines nicely with Groth-Sahai proofs, and thus could be of independent interest
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Efficient Distributed Tag-Based Encryption and its Application to Group Signatures with Efficient Distributed Traceability
Full text linkIn this work, we first formalize the notion of dynamic group signatures with distributed traceability, where the capability to trace signatures is distributed among nmanagers without requiring any interaction. This ensures that only the participation of all tracing managers permits tracing a signature, which reduces the trust placed in a single tracing manager. The threshold variant follows easily from our definitions and constructions. Our model offers strong security requirements. Our second contribution is a generic construction for the notion which has a concurrent join protocol, meets strong security requirements, and offers efficient traceability, i.e. without requiring tracing managers to produce expensive zero-knowledge proofs for tracing correctness. To dispense with the expensive zero-knowledge proofs required in the tracing, we deploy a distributed tag-based encryption with public verifiability. Finally, we provide some concrete instantiations, which, to the best of our knowledge, are the first efficient provably secure realizations in the standard model simultaneously offering all the aforementioned properties. To realize our constructions efficiently, we construct an efficient distributed (and threshold) tag-based encryption scheme that works in the efficient Type-III asymmetric bilinear groups. Our distributed tag-based encryption scheme yields short ciphertexts (only 1280 bits at 128-bit security), and is secure under an existing variant of the standard decisional linear assumption. Our tag-based encryption scheme is of independent interest and is useful for many applications beyond the scope of this paper. As a special case of our distributed tag-based encryption scheme, we get an efficient tag-based encryption scheme in Type-III asymmetric bilinear groups that is secure in the standard model
Stronger Security Notions for Decentralized Traceable Attribute-Based Signatures and More Efficient Constructions
Full text linkAbstract. Traceable attribute-based signatures extend standard attribute-based signatures by granting a desig-nated tracing authority the power to revoke the anonymity of signatures by revealing who signed them. Such a feature is important in deterring abuse and enforcing accountability. In this work, we revisit the notion of Decentralized Traceable Attribute-Based Signatures (DTABS) introduced by El Kaafarani et al. (CT-RSA 2014) and improve the state-of-the-art in two directions: Firstly, we provide a new stronger security model which circumvents some shortcomings in existing models. Our model minimizes the trust placed in attribute authorities and hence provides, among other things, a stronger definition for non-frameability. In addition, unlike previous models, our model captures the notion of tracing soundness which ensures that even if all parties in the system are fully corrupt, no one but the user who produced the signa-ture could claim authorship of the signature. Secondly, we provide a generic construction that is secure w.r.t. our strong security model and show two example instantiations in the standard model which are much more efficient than existing constructions (secure under weaker security definitions)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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