1745284
On Simulation-Sound Trapdoor Commitments
We study the recently introduced notion of a simulation-sound trapdoor commitment (SSTC) scheme. In this paper, we present a new, simpler definition for an SSTC scheme that admits more efficient constructions and can be used in a larger set of applications. Specifically, we show how to construct SSTC schemes from any one-way functions, and how to construct very efficient SSTC schemes based on specific number-theoretic assumptions. We also show how to construct simulation-sound, non-malleable, and universally-composable zero-knowledge protocols using SSTC schemes, yielding, for instance, the most efficient universally-composable zero-knowledge protocols known. Finally, we explore the relation between SSTC schemes and non-malleable commitment schemes by presenting a sequence of implication and separation results, which in particular imply that SSTC schemes are non-malleable.
5253044
Towards the classical communication complexity of entanglement distillation protocols with incomplete information
Entanglement is an essential resource for quantum communication and quantum computation, similar to shared random bits in the classical world. Entanglement distillation extracts nearly-perfect entanglement from imperfect entangled state. The classical communication complexity of these protocols is the minimal amount of classical information that needs to be exchanged for the conversion. In this paper, we focus on the communication complexity of protocols that operate with incomplete information, i.e., where the inputs are mixed states and/or prepared adversarially. We consider three models of imperfect entanglement, namely, the bounded measurement model, the depolarization model, and the fidelity model. We describe these models as well as the motivations for studying them. For the bounded measurement model and the depolarization model, we prove tight and almost-tight bounds on the output quality of non-interactive protocols. For the fidelity model, we prove a lower bound that matches the upper bound given by Ambainis et al., and thus completely characterizes communication complexity of entanglement distillation protocols for this model. Our result also suggests the optimality of the BB84 protocol in terms of communication complexity. We emphasize that although some of the results appear intuitively straightforward, their proofs are not. In fact, two novel techniques are developed for proving these results. We believe that these techniques are of independent interests, too.
61091746
Resource Fairness and Composability of Cryptographic Protocols
We introduce the notion of resource-fair protocols. Informally, this property states that if one party learns the output of the protocol, then so can all other parties, as long as they expend roughly the same amount of resources. As opposed to similar previously proposed definitions, our definition follows the standard simulation paradigm and enjoys strong composability properties. In particular, our definition is similar to the security definition in the universal composability (UC) framework, but works in a model that allows any party to request additional resources from the environment to deal with dishonest parties that may prematurely abort. 
 
In this model we specify the ideally fair functionality as allowing parties to “invest resources” in return for outputs, but in such an event offering all other parties a fair deal. (The formulation of fair dealings is kept independent of any particular functionality, by defining it using a “wrapper.”) Thus, by relaxing the notion of fairness, we avoid a well-known impossibility result for fair multi-party computation with corrupted majority; in particular, our definition admits constructions that tolerate arbitrary number of corruptions. We also show that, as in the UC framework, protocols in our framework may be arbitrarily and concurrently composed. 
 
Turning to constructions, we define a “commit-prove-fair-open” functionality and design an efficient resource-fair protocol that securely realizes it, using a new variant of a cryptographic primitive known as “time-lines.” With (the fairly wrapped version of) this functionality we show that some of the existing secure multi-party computation protocols can be easily transformed into resource-fair protocols while preserving their security.
45289699
Strengthening Zero-Knowledge Protocols Using Signatures
Recently there has been an interest in zero-knowledge protocols with stronger properties, such as concurrency, unbounded simulation soundness, non-malleability, and universal composability. In this paper, we show a novel technique to convert a large class of existing honest-verifier zero-knowledge protocols into ones with these stronger properties in the common reference string model. More precisely, our technique utilizes a signature scheme existentially unforgeable against adaptive chosen-message attacks, and transforms any Σ-protocol (which is honest-verifier zero-knowledge) into an unbounded simulation sound concurrent zero-knowledge protocol. We also introduce Ω-protocols, a variant of Σ-protocols for which our technique further achieves the properties of non-malleability and/or universal composability. 
 
In addition to its conceptual simplicity, a main advantage of this new technique over previous ones is that it avoids the Cook-Levin theorem, which tends to be rather inefficient. Indeed, our technique allows for very efficient instantiation based on the security of some efficient signature schemes and standard number-theoretic assumptions. For instance, one instantiation of our technique yields a universally composable zero-knowledge protocol under the Strong RSA assumption, incurring an overhead of a small constant number of exponentiations, plus the generation of two signatures.
195911179
Extracting Quantum Entanglement
We study the problem of extracting EPR pairs from a general source of entanglement. Suppose Alice and Bob share a bipartite state R which is "reasonably close" to perfect EPR pairs. The only information Alice and Bob possess is a lower bound on the fidelity of R and a maximally entangled state. They wish to "purify" R using local operations and classical communication and output a state that is arbitrarily close to EPR pairs. We prove that on average, Alice and Bob cannot increase the fidelity of the input state significantly. On the other hand, there exist protocols that may fail with a small probability, and otherwise will output states arbitrarily close to EPR pairs with very high probability. These protocols come from the "purity-testing protocols" of Barnum et al.
5335881
On statistical query sampling and NMR quantum computing
We introduce a "statistical query sampling" model, in which the goal of an algorithm is to produce an element in a hidden set S/spl sube/{0,1}/sup n/ with reasonable probability. The algorithm gains information about S through oracle calls (statistical queries), where the algorithm submits a query function g(/spl middot/) and receives an approximation to Pr/sub x/spl isin/S/[g(x)=1]. We show how this model is related to NMR quantum computing, in which only statistical properties of an ensemble of quantum systems can be measured, and in particular to the question of whether one can translate standard quantum algorithms to the NMR setting without putting all of their classical postprocessing into the quantum system. Using Fourier analysis techniques developed in the related context of statistical query learning, we prove a number of lower bounds (both information-theoretic and cryptographic) on the ability of algorithms to produce an x/spl isin/S, even when the set S is fairly simple. These lower bounds point out a difficulty in efficiently applying NMR quantum computing to algorithms such as Shor's and Simon's algorithm that involve significant classical postprocessing. We also explicitly relate the notion of statistical query sampling to that of statistical query learning.
11653478
Design and empirical evaluation of search software for legal professionals on the WWW
Abstract Our research focuses on designing effective search aids for legal researchers interested in law-related information on the world wide web. In this paper we report on the design and evaluation of two software systems developed to explore models for browsing and searching across a user-selected set of WWW sites. A directory services tool, LIBClient, provides a hierarchical index of legal information resources in an interface emphasizing ease-of-use by Internet novices and management of multiple-site searching. To study the relative effectiveness of LIBClient in the hands of legal professionals, nineteen law students were observed using LIBClient and, in separate trials, the popular general-purpose search services to perform known-item searches within a fixed time limit. The experiment indicates the value of LIBClient for focused searching, most properly as a supplement to general-purpose search engines. Motivated by observations from the LIBClient study, a second retrieval experiment explores the effectiveness of a radically different LIBClient design in which the LIBClient interface is combined with a crawler-enhanced search engine, IRISWeb. The LIBClient–IRISWeb system enables full-text searching using natural language queries across a set of WWW pages collected by the IRISWeb crawler. The page harvesting process relies on a cascading set of filters to define the final set of WWW pages to be collected, including user selections in LIBClient, search results from site-specific search engines, and the hyperlink structure at target sites. To evaluate the LIBClient–IRISWeb method, the queries used in the user study are submitted to the system, with excellent retrieval results. In conclusion, our research points to the promise of WWW search tool designs that tightly couple directed browsing with query-based search capabilities using new forms of search automation.
6906500
Web Appearance Disambiguation of Personal Names Based on Network Motif
Searching for information about a particular person is a common activity on search engines. However, current search engines do not provide any special function for search a person. Previous research has solved the problem by using additional background knowledge, such as a friend list, to cluster the searched Web pages. However, it is still difficult to retrieve and choose suitable background knowledge. In this paper, we propose a Web appearance disambiguation (WAD) system to solve the problem by only using the hyperlink structures between Web pages. The key idea of the WAD system is to find out smaller node motifs as evidences of close relationship between pages for clustering searched Web pages. Our experimental results show that, under no background knowledge, the performance of the WAD system achieves 70% for the F-measure
3129932
An efficient method to find area clusters with constraints using grid index structure
This work presents an efficient method to find area clusters satisfying certain constraints. The method uses a grid index structure to find them by examining five cell, 8-connected neighborhood. The hierarchical clustering technique is applied for preprocessing the grid with similar value distribution into the same clusters. This preprocessing helps reduce the computational time and eliminate the possible outlier grid cells. The constraints are average value range, minimum area size and minimum missing data ratio. The method is implemented for a remote sensing data, MOD08/spl I.bar/M3, which is MODIS (MODerate resolution Imaging Spectroradiometer) level 3 monthly atmospheric product.
29113389
Approximate string matching in LDAP based on edit distance
As the E-Commerce rapidly grows up, searching data is almost necessary in every application. Approximate string matching problems play a very important role to search with errors. Against these problems "Edit distance" and "Soundex" are two common techniques, especially the latter one is a "sound-like" method and had been applied to the LDAP server. Nevertheless, it is not adequate for certain situations especially when we perform the symbol matching (as in DNA); it doesn't make sense to use the "sound-like" method. On the other hand, "Edit distance" has a clear definition and also is widely used in many fields of application. Since the design of LDAP server is optimized for reading, applying edit distance technique to LDAP server has the problem of lowering speed. In this paper we design efficient data structures and an algorithm to solve the speed problem, and furthermore we use three filter conditions [1] based on the n-gram technique to achieve a well filter performance. Finally we also demonstrate experimentally the benefits of applying our algorithm and its limitations.
26832202
Approximate search engine optimization for directory service
Today, in many practical e-commerce systems, the real stored data usually are short strings, such as names, addresses, or other information. Searching data within these short strings is not the same as searching within longer strings. General search engines try their best to scan all long strings (or articles) quickly, and find out the places that match the search conditions. Some great online search algorithms (such as "agrep" as used inside glimpse, or "cgrep " as used inside compressed indices, or 'NR-grep') are proposed for searching without any indices in the sub-linear time O(n). However, for short strings (n is small), the practical performance of algorithms of O(n) and O(n) are much the same. Therefore, suitable indices are necessary to optimize the performance of the search engine. On the other hand, directory services are more and more important because of its optimization for searching data. The data stored in directory servers are almost short strings. The approximate search engine for directory service must take the properties of short strings into considerations. In our previous research, we have designed one approximate search engine especially for short strings by using filters to filter out the possible short strings, and then checking for the answers. However the performance of the previous search engine needs to be enhanced. In this paper, we propose new architecture and algorithm to optimize the performance of searching for directory service.