다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Networks beyond pairwise interactions: Structure and dynamics

We present Path ORAM, an extremely simple Oblivious RAM protocol with a small amount of client storage. Partly due to its simplicity, Path ORAM is the most practical ORAM scheme for small client storage known to date. We formally prove that Path ORAM requires log^2 N / log X bandwidth overhead for block size B = X log N. For block sizes bigger than Omega(log^2 N), Path ORAM is asymptotically better than the best known ORAM scheme with small client storage. Due to its practicality, Path ORAM has been adopted in the design of secure processors since its proposal.

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Path ORAM: an extremely simple oblivious RAM protocol

Stephen J. Hartley Oxford University Press, New York, 1998, 260 pp. ISBN 0-19-511315-2, $45.00 Concurrent Programming  is a thorough treatment of Java multi-threaded programming for both a stand-alone and distributed environment. Designed mostly for students in concurrent or parallel programming classes, the text is also an excellent reference for the practicing professional developing multi-threaded programs or applets. Hartley first provides a complete explanation of the features of Java necessary to write concurrent programs, including topics such as exception handling, interfaces, and packages. He then gives the reader a solid background to write multi-threaded programs and also presents the problems introduced when writing concurrent programs—namely race conditions, mutual exclusion, and deadlock. Hartley also provides several software solutions that do not require the use of common process and thread mechanisms. Once the groundwork is laid for writing concurrent programs, Hartley then takes a different approach than most Java references. Rather than presenting how Java handles mutual exclusion with the  synchronized  keyword (although it is covered later), he first looks at semaphore-based solutions to classic concurrent problems such as bounded-buffer, readers-writers, and the dining philosophers. Hartley also uses the same approach to develop Java classes for monitors and message passing. This unique approach to introducing concurrency allows the readers to both understand how Java threads are synchronized and how the basic synchronization mechanism can be used to construct more abstract tools such as semaphores. If there is a shortcoming with the text it is with the lack of sufficient coverage of remote method invocation (RMI), although there is a section covering RMI. This is quite understandable as RMI is a fairly recent phenomenon with the Java community. Also, the classes that Hartley provides could easily implement RMI rather than sockets to handle communication. The strengths of the book include its ease in reading, several examples at the end of chapters, a package similar to Xtango that provides algorithm animation, and a supportive web site by the author (see  www.mcs.drexel.edu/~shartley/ConcProgJava/index.html ) including compressed source code. As Java becomes more dominant on the server side of multi-tier applications, writing thread-safe concurrent applications becomes even more important.  Concurrent Programming  is a strong step towards teaching students and professionals such skills. Greg Gagne, Westminster College of Salt Lake City Salt Lake City, Utah

Distributed Computing: Fundamentals, Simulations and Advanced Topics

What manner of organization is the National Bureau of Economic Research? How does it select research topics? Who does the work and what kind of tasks do they perform? Where do the funds come from? How does the National Bureau safeguard the scientific quality of its findings? How are the results disseminated? Visitors to the National Bureau often ask these and similar questions; perhaps the answers will be of interest to readers of the American Statistician. The National Bureau of Economic Research is a private non-profit corporation, formed, according to its charter, "to conduct, or assist in the making of exact and impartial investigations in the field of economic, social and industrial science, and to this end to cooperate with governments, universities, learned societies, and individuals." Hence it is not a government agency, nor an adjunct of a university, nor does it sell research services. The revenue from the only products it does sell, publications, barely covers the printing costs. Its funds are contributed by philanthropic foundations, by trade and professional organizations, by business concerns, trade unions, and individuals. Contributions are usually on a yearly basis, but some grants cover several years. Some of the funds are earmarked for specific studies; the balance goes to support a general program of research. The National Bureau is governed by a Board of Directors numbering about thirty, selected to represent various institutions and diverse points of view on economic problems. Over the years since the Bureau was founded in 1920 this body of men has made a significant contribution to the development of scientific inquiry in economics, both within the National Bureau and outside. Such outstanding economists as Wesley C. Mitchell, George E. Roberts, Allyn A. Young, Edwin F. Gay, Thomas S. Adams, and John R. Commons have been among its members. At the present time professors from a dozen universities are on the Board. Also, Directors from each of the following organizations are elected: American Statistical Association, American Economic Association, American Farm Economic Association, Economic History Association, American Institute of Accountants, American Management Association, Congress of Industrial Organizations, and American Federation of Labor. Finally, there is a group of Directors at Large, men from varied walks of life with an abiding interest in economic research. The Board serves an important function not only in shaping the broad lines of the research program but also in safeguarding the quality of the results. Matters of policy requiring prompt action are handled by an Executive Committee of eleven, elected by the Board from its membership. Arthur F. Burns, the Director of Research, is the member of the Committee who is directly responsible for the research program. The members of the research staff, numbering about twenty-five, direct the individual studies, and are aided in their work by upwards of forty-five research assistants. A staff of typists, bookkeepers, mimeograph operators, etc., brings the total payroll of the National Bureau to roughly a hundred persons. William J. Carson, the Executive Director, handles the Bureau's finances, accounts, and other administrative matters. Not all the employees of the National Bureau work at the main office at 1819 Broadway, New York City. DuLr Financial Research Program is housed at "Hillside," an estate about 10 miles north of Manhattan overlooking the HuLdson River. Other National BureauL investigators are to be fotund at various universities throughout the United States, since cooperative arrangements are maintained with a number of universities that permit their facultv members to engage in National Butreau studies. Government agencies, too, cooperate in similar ways. Such cooperative relationships are a vital feature of our work, and we try to foster them in many ways. The growing acceptance on the part of universities of the view that research is part of the job of a faculty member has helped to make these efforts productive. For example, for a number of years we have appointed promising young men or women holding university positions as Research Associates for one year. The objective is to enable scholars to pursue their research interests in fields in which the National Bureau also has an interest. Since 1930 twenty-six Research Associates, coming from eighteen American colleges or universities and two foreign universities, have been appointed under the plan. The work of several committees is another example of cooperation for the purpose of advancing research. Two committees, one on financial and the other on fiscal research, help to guide our studies in these areas. They are composed of experts from universities, government agencies, and private business. In 1935 the Universities-National Bureau Committee was established for the express purpose of promoting contact

The National Bureau of Economic Research

We design novel, asymptotically more efficient data structures and algorithms for programs whose data access patterns exhibit some degree of predictability. To this end, we propose two novel techniques, a pointer-based technique and a locality-based technique. We show that these two techniques are powerful building blocks in making data structures and algorithms oblivious. Specifically, we apply these techniques to a broad range of commonly used data structures, including maps, sets, priority-queues, stacks, deques; and algorithms, including a memory allocator algorithm, max-flow on graphs with low doubling dimension, and shortest-path distance queries on weighted planar graphs. Our oblivious counterparts of the above outperform the best known ORAM scheme both asymptotically and in practice.

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Oblivious Data Structures

Oblivious RAMs (ORAMs) have traditionally been measured by their bandwidth overhead and client storage. We observe that when using ORAMs to build secure computation protocols for RAM programs, the size of the ORAM circuits is more relevant to the performance. We therefore embark on a study of the circuit-complexity of several recently proposed ORAM constructions. Our careful implementation and experiments show that asymptotic analysis is not indicative of the true performance of ORAM in secure computation protocols with practical data sizes. We then present SCORAM, a heuristic compact ORAM design optimized for secure computation protocols. Our new design is almost 10x smaller in circuit size and also faster than all other designs we have tested for realistic settings (i.e., memory sizes between 4MB and 2GB, constrained by 2-80 failure probability). SCORAM makes it feasible to perform secure computations on gigabyte-sized data sets.

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SCORAM: Oblivious RAM for Secure Computation

We consider distributed private data analysis, where n parties each holding some sensitive data wish to compute some aggregate statistics over all parties' data. We prove a tight lower bound for the private distributed summation problem. Our lower bound is strictly stronger than the prior lower-bound result by Beimel, Nissim, and Omri published in CRYPTO 2008. In particular, we show that any n-party protocol computing the sum with sparse communication graph must incur an additive error of $\Omega(\sqrt{n})$ with constant probability, in order to defend against potential coalitions of compromised users. Furthermore, we show that in the client-server communication model, where all users communicate solely with an untrusted server, the additive error must be $\Omega(\sqrt{n})$, regardless of the number of messages or rounds. Both of our lower-bounds, for the general setting and the client-to-server communication model, are strictly stronger than those of Beimel, Nissim and Omri, since we remove the assumption on the number of rounds (and also the number of messages in the client-to-server communication model). Our lower bounds generalize to the (e, δ) differential privacy notion, for reasonably small values of δ.

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Optimal lower bound for differentially private multi-party aggregation

Finding dense subgraphs in large graphs is a key primitive in a variety of real-world application domains, encompassing social network analytics, event detection, biology, and finance. In most such applications, one typically aims at finding several (possibly overlapping) dense subgraphs which might correspond to communities in social networks or interesting events. While a large amount of work is devoted to finding a single densest subgraph, perhaps surprisingly, the problem of finding several dense subgraphs with limited overlap has not been studied in a principled way, to the best of our knowledge. In this work we define and study a natural generalization of the densest subgraph problem, where the main goal is to find at most $k$ subgraphs with maximum total aggregate density, while satisfying an upper bound on the pairwise Jaccard coefficient between the sets of nodes of the subgraphs. After showing that such a problem is NP-Hard, we devise an efficient algorithm that comes with provable guarantees in some cases of interest, as well as, an efficient practical heuristic. Our extensive evaluation on large real-world graphs confirms the efficiency and effectiveness of our algorithms.

/pdf/finding-subgraphs-with-maximum-total-density-and-limited-4bdogk4i5f.pdf

Finding Subgraphs with Maximum Total Density and Limited Overlap

As Byzantine Agreement (BA) protocols find application in large-scale decentralized cryptocurrencies, an increasingly important problem is to design BA protocols with improved communication complexity. A few existing works have shown how to achieve subquadratic BA under an {\it adaptive} adversary. Intriguingly, they all make a common relaxation about the adaptivity of the attacker, that is, if an honest node sends a message and then gets corrupted in some round, the adversary {\it cannot erase the message that was already sent} --- henceforth we say that such an adversary cannot perform "after-the-fact removal". By contrast, many (super-)quadratic BA protocols in the literature can tolerate after-the-fact removal. In this paper, we first prove that disallowing after-the-fact removal is necessary for achieving subquadratic-communication BA. 
Next, we show new subquadratic binary BA constructions (of course, assuming no after-the-fact removal) that achieves near-optimal resilience and expected constant rounds under standard cryptographic assumptions and a public-key infrastructure (PKI) in both synchronous and partially synchronous settings. In comparison, all known subquadratic protocols make additional strong assumptions such as random oracles or the ability of honest nodes to erase secrets from memory, and even with these strong assumptions, no prior work can achieve the above properties. Lastly, we show that some setup assumption is necessary for achieving subquadratic multicast-based BA.

T-H. Hubert Chan

Papers

Oblivious Data Structures

SCORAM: Oblivious RAM for Secure Computation

Optimal lower bound for differentially private multi-party aggregation

Finding Subgraphs with Maximum Total Density and Limited Overlap

Communication Complexity of Byzantine Agreement, Revisited