1,721,032 research outputs found
Black-Box Uselessness: Composing Separations in Cryptography
Get PDFBlack-box separations have been successfully used to identify the limits of a powerful set of tools in cryptography, namely those of black-box reductions. They allow proving that a large set of techniques are not capable of basing one primitive on another . Such separations, however, do not say anything about the power of the combination of primitives ₁,₂ for constructing , even if cannot be based on ₁ or ₂ alone.
By introducing and formalizing the notion of black-box uselessness, we develop a framework that allows us to make such conclusions. At an informal level, we call primitive black-box useless (BBU) for if cannot help constructing in a black-box way, even in the presence of another primitive . This is formalized by saying that is BBU for if for any auxiliary primitive , whenever there exists a black-box construction of from (,), then there must already also exist a black-box construction of from alone. We also formalize various other notions of black-box uselessness, and consider in particular the setting of efficient black-box constructions when the number of queries to is below a threshold.
Impagliazzo and Rudich (STOC'89) initiated the study of black-box separations by separating key agreement from one-way functions. We prove a number of initial results in this direction, which indicate that one-way functions are perhaps also black-box useless for key agreement. In particular, we show that OWFs are black-box useless in any construction of key agreement in either of the following settings: (1) the key agreement has perfect correctness and one of the parties calls the OWF a constant number of times; (2) the key agreement consists of a single round of interaction (as in Merkle-type protocols). We conjecture that OWFs are indeed black-box useless for general key agreement.
We also show that certain techniques for proving black-box separations can be lifted to the uselessness regime. In particular, we show that the lower bounds of Canetti, Kalai, and Paneth (TCC'15) as well as Garg, Mahmoody, and Mohammed (Crypto'17 & TCC'17) for assumptions behind indistinguishability obfuscation (IO) can be extended to derive black-box uselessness of a variety of primitives for obtaining (approximately correct) IO. These results follow the so-called "compiling out" technique, which we prove to imply black-box uselessness.
Eventually, we study the complementary landscape of black-box uselessness, namely black-box helpfulness. We put forth the conjecture that one-way functions are black-box helpful for building collision-resistant hash functions. We define two natural relaxations of this conjecture, and prove that both of these conjectures are implied by a natural conjecture regarding random permutations equipped with a collision finder oracle, as defined by Simon (Eurocrypt'98). This conjecture may also be of interest in other contexts, such as amplification of hardness
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
New Protocols for Secure Equality Test and Comparison
Get PDFProtocols for securely comparing private values are among the most fundamental building blocks of multiparty computation. Introduced by Yao under the name millionaire\u27s problem, they have found numerous applications in a variety of privacy-preserving protocols; however, due to their inherent non-arithmetic structure, existing construction often remain an important bottleneck in large-scale secure protocols.
In this work, we introduce new protocols for securely computing the greater-than and the equality predicate between two parties. Our protocols rely solely on the existence of oblivious transfer, and are UC-secure against passive adversaries. Furthermore, our protocols are well suited for use in large-scale secure computation protocols, where secure comparisons (SC) and equality tests (ET) are commonly used as basic routines: they perform particularly well in an amortized setting, and can be preprocessed efficiently (they enjoy an extremely efficient, information-theoretic online phase). We perform a detailed comparison of our protocols to the state of the art, showing that they improve over the most practical existing solutions regarding both communication and computation, while matching the asymptotic efficiency of the best theoretical constructions
Revisiting Covert Multiparty Computation
Get PDFIs it feasible for parties to securely evaluate a function on their joint inputs, while hiding not only their private input, but even the very fact that they are taking part to the protocol? This intriguing question was given a positive answer in the two-party case at STOC’05, and in the general case at FOCS’07, under the name of covert multiparty computation (CMPC). A CMPC protocol allows n players with inputs (x1 ···xn) to compute a function f with the following guarantees:
– If all the parties are taking part to the protocol, and if the result of the computation is favorable to all the parties, then they get to learn f(x1,··· ,xn) (and nothing more)
– Else, when the result is not favorable to all the parties, or if some player does not participate to the computation, no one gets to learn anything (and in particular, no player can learn whether any of the other parties was indeed participating to the protocol)
While previous works proved the existence of CMPC under standard assumptions, their candidate CMPC protocols were exclusively of theoretical interest. In this work, we revisit the design of CMPC protocols and show that, perhaps surprisingly, this very strong security notion can be achieved essentially for free. More specifically, we show how to build a CMPC protocol out of a standard, state-of-the-art MPC protocol, where both the communication and the computation are the same than the original protocol, up to an additive factor independent of the size of the circuit. Along the way, we prove two variants of the UC theorem which greatly simplify the design and the security analysis of CMPC protocols
A Note on the Communication Complexity of Multiparty Computation in the Correlated Randomness Model
Get PDFSecure multiparty computation (MPC) addresses the challenge of evaluating functions on secret inputs without compromising their privacy. An central question in multiparty communication is to understand the amount of communication needed to securely evaluate a circuit of size s. In this work, we revisit this fundamental question, in the setting of information-theoretically secure MPC in the correlated randomness model, where a trusted dealer distributes correlated random coins, independent of the inputs, to all parties before the start of the protocol. This setting is of strong theoretical interest, and has led to the most practically efficient MPC protocols known to date.
While it is known that protocols with optimal communication (proportional to input plus output size) can be obtained from the LWE assumption, and that protocols with sublinear communication o(s) can be obtained from the DDH assumption, the question of constructing protocols with o(s) communication remains wide open for the important case of information-theoretic MPC in the correlated randomness model. All known protocols in this model require O(s) communication in the online phase; improving this state of affairs is a long standing open question. In this work, we exhibit the first generic multiparty computation protocol in the correlated randomness model with communication sublinear in the circuit size, for a large class of circuits. More precisely, we show the following: any size-s layered circuit (whose nodes can be partitioned into layers so that any edge connects adjacent layers) can be evaluated with O(s/log log s) communication. Our results holds for both boolean and arithmetic circuits, in the honest-but-curious setting, and do not assume honest majority. For boolean circuits, we extend our results to handle malicious corruption
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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