1,721,010 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
A Note on the Indifferentiability of the 10-Round Feistel Construction
Get PDFAbstract. Holenstein et al. (STOC 2011) have shown that the Feistel construction with fourteen rounds and public random round functions is indifferentiable from a random permutation. In the same paper, they pointed out that a previous proof for the 10-round Feistel construction by Seurin (PhD thesis) was flawed. However, they left open the question of whether the proof could be patched (leaving hope that the simulator described by Seurin could still be used to prove indifferentiability of the 10-round Feistel construction). In this note, we show that the proof cannot be patched (and hence that the simulator described by Seurin cannot be used to prove the indifferentiability of the 10-round Feistel construction) by describing a distinguishing attack that succeeds with probability close to one against this simulator. We stress that this does not imply that the 10-round Feistel construction is not indifferentiable from a random permutation (since our attack does not exclude the existence of a different simulator that would work).
On the Lossiness of the Rabin Trapdoor Function ⋆
Get PDFAbstract. Lossy trapdoor functions, introduced by Peikert and Waters (STOC ’08), are functions that can be generated in two indistinguishable ways: either the function is injective, and there is a trapdoor to invert it, or the function is lossy, meaning that the size of its range is strictly smaller than the size of its domain. Kakvi and Kiltz (EUROCRYPT 2012) proved that the Full Domain Hash signature scheme based on a lossy trapdoor function has a tight security reduction from the lossiness of the trapdoor function. Since Kiltz, O’Neill, and Smith (CRYPTO 2010) showed that the RSA trapdoor function is lossy under the Φ-Hiding assumption of Cachin, Micali, and Stadler (EUROCRYPT ’99), this implies that the RSA Full Domain Hash signature scheme has a tight security reduction from the Φ-Hiding assumption (for public exponents e < N 1/4). In this work, we consider the Rabin trapdoor function, i.e. modular squaring over Z ∗ N. We show that when adequately restricting its domain (either to the set QRN of quadratic residues, or to (JN) +, the set of positive integers 1 ≤ x ≤ (N − 1)/2 with Jacobi symbol +1) the Rabin trapdoor function is lossy, the injective mode corresponding to Blum integers N = pq with p, q ≡ 3 mod 4, and the lossy mode corresponding to what we call pseudo-Blum integers N = pq with p, q ≡ 1 mod 4. This lossiness result holds under a natural extension of the Φ-Hiding assumption to the case e = 2 that we call the 2-Φ/4-Hiding assumption. We then use this result to prove that deterministic variants of Rabin-Williams Full Domain Hash signatures have a tight reduction from the 2-Φ/4-Hiding assumption. We also show that these schemes are unlikely to have a tight reduction from the factorization problem by extending a previous “meta-reduction ” result by Coron (EUROCRYPT 2002), later corrected by Kakvi and Kiltz (EUROCRYPT 2012). These two results therefore answer one of the main questions left open by Bernstein (EUROCRYPT 2008) in his work on Rabin-Williams signatures
On the Exact Security of Schnorr-Type Signatures in the Random Oracle Model
Get PDFThe Schnorr signature scheme has been known to be provably secure in the Random Oracle Model under the Discrete Logarithm (DL) assumption since the work of Pointcheval and Stern (EUROCRYPT \u2796), at the price of a very loose reduction though: if there is a forger making at most random oracle queries, and forging signatures with probability , then the Forking Lemma tells that one can compute discrete logarithms with constant probability by rewinding the forger times. In other words, the security reduction loses a factor in its time-to-success ratio. This is rather unsatisfactory since may be quite large. Yet Paillier and Vergnaud (ASIACRYPT 2005) later showed that under the One More Discrete Logarithm (OMDL) assumption, any \emph{algebraic} reduction must lose a factor at least in its time-to-success ratio. This was later improved by Garg~\emph{et al.} (CRYPTO 2008) to a factor . Up to now, the gap between and remained open. In this paper, we show that the security proof using the Forking Lemma is essentially the best possible. Namely, under the OMDL assumption, any algebraic reduction must lose a factor in its time-to-success ratio, where is a function that remains close to 1 as long as is noticeably smaller than 1. Using a formulation in terms of expected-time and queries algorithms, we obtain an optimal loss factor , independently of . These results apply to other signature schemes based on one-way group homomorphisms, such as the Guillou-Quisquater signature scheme
Variations on the Author
Get PDF“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
New Constructions and Applications of Trapdoor DDH Groups
Get PDFTrapdoor Decisional Diffie-Hellman (TDDH) groups, introduced by Dent and Galbraith (ANTS 2006), are groups where the DDH problem is hard, unless one is in possession of a secret trapdoor which enables solving it efficiently. Despite their intuitively appealing properties, they have found up to now very few cryptographic applications. Moreover, among the two constructions of such groups proposed by Dent and Galbraith, only a single one based on hidden pairings remains unbroken.
In this paper, we extend the set of trapdoor DDH groups by giving a construction based on composite residuosity. We also introduce a more restrictive variant of these groups that we name \emph{static} trapdoor DDH groups, where the trapdoor only enables to solve the DDH problem with respect to a fixed pair of group elements. We give two constructions for such groups whose security relies respectively on the RSA and the factoring assumptions. Then, we show that static trapdoor DDH groups yield elementary constructions of convertible undeniable signature schemes allowing delegatable verification. Using our constructions of static trapdoor DDH groups from the RSA or the factoring assumption, we obtain slightly simpler variants of the undeniable signature schemes of respectively Gennaro, Rabin, and Krawczyk (J. Cryptology, 2000) and Galbraith and Mao (CT-RSA 2003). These new schemes are conceptually more satisfying since they can strictly be viewed as instantiations, in an adequate group, of the original undeniable signature scheme of Chaum and van Antwerpen (CRYPTO~\u2789)
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
The security of Mimblewimble
No full textMimblewimble is a payment protocol that underlies several cryptocurrencies and is now also supported by Litecoin. Besides offering privacy by design, it improves on scalability: while in Bitcoin every transaction must be stored forever, in Mimblewimble only the "unspent transaction outputs", which represent the current state of the system, must be kept. In joint work with Michele Orrù and Yannick Seurin, we have formally shown the security of Mimblewimble (EUROCRYPT'19), as well as that of a recent extension (ia.cr/2022/265)
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