1,720,977 research outputs found
An algebraic approach to Nonmalleability
No full textIn their seminal work on nonmalleable cryptography, Dolev, Dwork, and Naor showed how to construct a nonmalleable commitment with logarithmically-many ``rounds""/``slots,"" the idea being that any adversary may successfully maul in some slots but would fail in at least one. Since then new ideas have been introduced, ultimately resulting in constant-round protocols based on any one-way function. Yet, in spite of this remarkable progress, each of the known constructions of nonmalleable commitments leaves something to be desired. In this paper we propose a new technique that allows us to construct a nonmalleable protocol with only a single slot and to improve in at least one aspect over each of the previously proposed protocols. Two direct byproducts of our new ideas are a four-round nonmalleable commitment and a four-round nonmalleable zero-knowledge argument, the latter matching the round-complexity of the best known zero-knowledge argument (without the nonmalleability requirement). The protocols are based on the existence of one-way functions and admit very efficient instantiations via standard homomorphic commitments and sigma protocols. Our analysis relies on algebraic reasoning, and makes use of error correcting codes in order to ensure that committers' tags differ in many coordinates. One way of viewing our construction is as a method for combining many atomic subprotocols in a way that simultaneously amplifies soundness and nonmalleability, thus requiring much weaker guarantees to begin with, and resulting in a protocol which is much trimmer in complexity compared to the existing ones
Cryptanalysis of Two Fault Countermeasure Schemes
Full text linkIn this paper, we look at two fault countermeasure schemes proposed very recently in literature. The first proposed in ACISP 2015 constructs a transformation function using a cellular automata based linear diffusion, and a non-linear layer using a series of bent functions. This countermeasure is meant for the protection of block ciphers like AES. The second countermeasure was proposed in IEEE-HOST 2015 and protects the Grain-128 stream cipher. The design divides the output function used in Grain-128 into two components. The first called the masking function, masks the input bits to the output function with some additional randomness and computes the value of the function. The second called the unmasking function, is computed securely using a different register and undoes the effect of the masking with random bits. We will show that there exists a weakness in the way in which both these schemes use the internally generated random bits which make these designs vulnerable. We will outline attacks that cryptanalyze the above schemes using 66 and 512 faults respectively
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
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
Kryptographische Uhren und Anwendungen
Full text linkIn this dissertation we define, construct, and build on cryptographic objects that simulate the
elapsing of time. This work concerns with tasks that involve the cryptographic equivalent of
a reference clock and allow one to prove that a certain amount of time units is passed or to
hide a secret for a predetermined amount of time. More specifically, we present the following
cryptographic primitives.
(1) Incremental Proofs of Sequential Work allow a prover to convince a verifier that a certain
amount of sequential work has been performed. Proofs can be passed on to new provers or
forked to new machines almost for free. Our constructions are essentially optimal in terms
of prover space and time complexity.
(2) Homomorphic Time-Lock Puzzles encapsulate secrets for a certain amount of time and allow
anyone to publicly compute functions over plaintexts without opening the puzzles. We
propose several instances for different function families and we show how to leverage them
as a solution for the scalability problems of classical time-lock puzzles.
(3) Multi-Hop Locks allow pairs of users to establish contracts such that coins are transacted
if a certain condition is satisfied within some time. They serve as the main cryptographic
building block to perform atomic multi-hop transactions in payment channel networks.In dieser Dissertation definieren, konstruieren und arbeiten wir mit kryptographischen Objekten,
die das Vergehen von Zeit simulieren. Diese Arbeit befasst sich mit Aufgaben, die das kryptographische
Äquivalent einer Referenzuhr beinhalten, und es einem ermöglichen, zu beweisen,
dass eine bestimmte Anzahl von Zeiteinheiten vergangen ist, oder ein Geheimnis für eine
vorgegebene Zeit zu verbergen. Genauer gesagt stellen wir die folgenden kryptographischen
Primitive vor.
(1) Inkrementelle Beweise sequentieller Arbeit ermöglichen es einem Beweisführer, einen
Verifizierer davon zu überzeugen, dass eine gewisse Menge an sequentieller Arbeit verrichtet
wurde. Beweise können nahezu ohne Mehraufwand an neue Beweisführer weitergegeben
oder auf neue Maschinen aufgeteilt werden. Unsere Konstruktionen sind in Bezug auf den
Speicherplatz des Beweisführers und Zeitkomplexität im Wesentlichen optimal.
(2) Homomorphe Zeitschlossrätsel verbergen Geheimnisse für einen bestimmten Zeitraum und
ermöglichen es jedem, öffentlich Funktionen über die Klartexte zu berechnen, ohne die
Rätsel zu lösen. Wir präsentieren einige Instanzen für verschiedene Familien von Funktionen
und zeigen, wie man diese als Lösung für die Skalierbarkeitsprobleme klassischer
Zeitschlossrätsel einsetzen kann.
(3) Multi-Hop-Schlösser ermöglichen es Benutzerpaaren, Verträge abzuschließen, so dass
Kryptowährungseinheiten überwiesen werden, wenn eine bestimmte Bedingung innerhalb
eines gewissen Zeitraums erfüllt ist. Sie dienen als kryptographischer Hauptbaustein zur
Durchführung atomarer Multi-Hop-Transaktionen in Zahlungskanalnetzwerken
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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