5424518
Round Efficiency of Multi-party Computation with a Dishonest Majority
We consider the round complexity of multi-party computation in the presence of a static adversary who controls a majority of the parties. Here, n players wish to securely compute some functionality and up to n - 1 of these players may be arbitrarily malicious. Previous protocols for this setting (when a broadcast channel is available) require O(n) rounds. We present two protocols with improved round complexity: The first assumes only the existence of trapdoor permutations and dense cryptosystems, and achieves round complexity O(log n) based on a proof scheduling technique of Chor and Rabin [13]; the second requires a stronger hardness assumption (along with the non-black-box techniques of Barak [2]) and achieves O(1) round complexity.
7418837
Lower bounds for collusion-secure fingerprinting
Collusion-secure fingerprinting codes are an important primitive used by many digital watermarking schemes [1, 10, 9]. Boneh and Shaw [3] define a model for these types of codes and present an explicit construction. Their code has length <i>O</i>(<i>c</i><sup>3</sup> log(l/ε)) and attains security against coalitions of size <i>c</i> with ε error. Boneh and Shaw also present a lower bound of Ω (<i>c</i><sup>3</sup>log(1/<i>c</i>ε)) on the length of any collusion-secure code.We give new lower bounds on the length of collusion-secure codes by analyzing a weighted coinflipping strategy for the coalition. As an illustration of our methods, we give a simple proof that the Boneh-Shaw construction cannot be asymptotically improved. Next, we prove a general lower bound: no secure code can have length <i>O</i>(<i>c</i><sup>2</sup>1og(1/<i>c</i>ε)), which improves the previous known bound by a factor of <i>c</i>. In particular, we show that any secure code will have length Ω(<i>c</i><sup>2</sup> log(1/<i>c</i>ε)) as long as log(l/ε) ≥ <i>K</i> <i>k</i> log <i>c</i>, where <i>K</i> is a constant and <i>k</i> is the number of columns in the code (in some sense, a measure of the code's complexity). Finally, we describe a general paradigm for constructing fingerprinting codes which encompasses the construction of [3], and show that no secure code that follows this paradigm can have length <i>O</i>((c<sup>3</sup>/log c) log(1/<i>c</i>ε)) follows this (again, by showing a lower bound for large values of ln(1/ε)). This suggests that any attempts at improvement should be directed toward techniques that lie outside our paradigm.
314094
Correcting errors without leaking partial information
This paper explores what kinds of information two parties must communicate in order to correct errors which occur in a shared secret string W. Any bits they communicate must leak a significant amount of information about W --- that is, from the adversary's point of view, the entropy of W will drop significantly. Nevertheless, we construct schemes with which Alice and Bob can prevent an adversary from learning any useful information about W. Specifically, if the entropy of W is sufficiently high, then there is no function f(W) which the adversary can learn from the error-correction information with significant probability.This leads to several new results: (a) the design of noise-tolerant "perfectly one-way" hash functions in the sense of Canetti et al. [7], which in turn leads to obfuscation of proximity queries for high entropy secrets W; (b) private fuzzy extractors [11], which allow one to extract uniformly random bits from noisy and nonuniform data W, while also insuring that no sensitive information about W is leaked; and (c) noise tolerance and stateless key re-use in the Bounded Storage Model, resolving the main open problem of Ding [10].The heart of our constructions is the design of strong randomness extractors with the property that the source W can be recovered from the extracted randomness and any string W' which is close to W.
1672422
Entropic Security and the Encryption of High Entropy Messages
We study entropic security, an information-theoretic notion of security introduced by Russell and Wang [24] in the context of encryption and by Canetti et al. [5,6] in the context of hash functions. Informally, a probabilitic map $Y = \mathcal{E}(X)$ (e.g., an encryption sheme or a hash function) is entropically secure if knowledge of Y does not help predicting any predicate of X, whenever X has high min-entropy from the adversary's point of view. On one hand, we strengthen the formulation of [5,6,24] and show that entropic security in fact implies that Y does not help predicting any function of X (as opposed to a predicate), bringing this notion closer to the conventioonal notion of semantic security [10]. On the other hand, we also show that entropic security is equivalent to indistinguishability on pairs of input distributions of sufficiently high entropy, which is in turn related to randomness extraction from non-uniform distributions [21]. 
 
We then use the equivalence above, and the connection to randomness extraction, to prove several new results on entropically-secure encryption. First, we give two general frameworks for constructing entropically secure encryption schemes: one based on expander graphs and the other on XOR-universal hash functions. These schemes generalize the schemes of Russell and Wang, yielding simpler constructions and proofs, as well as improved parameters. To encrypt an n-bit message of min-entropy t while allowing at most e-advantage to the adversary, our best schemes use a shared secret key of length $k = n - t + 2{\rm log} (\frac {1}{\epsilon})$. Second, we obtain lower bounds on the key length k for entropic security and indistinguishability. In particular, we show near tightness of our constructions: k > n – t. For a large class of schemes — including all the schemes we study — the bound can be strengthened to $k \geq n - t+{\rm log} (\frac {1}{\epsilon})-O(1)$.
1579170
Dataflow Predication
Predication facilitates high-bandwidth fetch and large static scheduling regions, but has typically been too complex to implement comprehensively in out-of-order micro architectures. This paper describes dataflow predication, which provides per-instruction predication in a dataflow ISA, low predication computation overheads similar to VLIW ISAs, and low complexity out-of-order issue. A two-bitfield in each instruction specifies whether an instruction is predicated, in which case, an arriving predicate token determines whether an instruction should execute. Dataflow predication incorporates three features that reduce predication overheads. First, dataflow predicate computation permits computation of compound predicates with virtually no overhead instructions. Second, early mispredication termination squashes in-flight instructions with false predicates at any time, eliminating the overhead of falsely predicated paths. Finally, implicit predication mitigates the fanout overhead of dataflow predicates by reducing the number of explicitly predicated instructions, by predicating only the heads of dependence chains. Dataflow predication also exposes new compiler optimizations - such as disjoint instruction merging and path-sensitive predicate removal - for increased performance of predicated code in an out-of-order design
33110075
Report of the Purdue Workshop on Grand Challenges in Computer Architecture for the Support of High Performance Computing
Abstract The “Purdue Workshop on Grand Challenges in Computer Architecture for the Support of High Performance Computing” was sponsored by the National Science Foundation to identify critical research topics in computer architecture as they relate to high performance computing. Following a wide-ranging discussion of the computational characteristics and requirements of the grand challenge applications, the workshop identified four major computer architecture grand challenges as crucial to advancing the state of the art of high performance computation in the coming decade. These are: (1) idealized parallel computer models; (2) usable peta-ops (1015 ops) performance; (3) computers in an era of HDTV, gigabyte networks, and visualization; and (4) infrastructure for prototyping architectures. This report overviews some of the demands of the grand challenge applications and presents the above four grand challenges for computer architecture.
6414828
Local Search Genetic Algorithm for Optimization of Highly Reliable Communications Networks
This paper presents a genetic algorithm (GA) with specialized encoding, initialization and local search genetic operators to optimize communication network topologies. This NPhard problem is often highly constrained so that random initialization and standard genetic operators usually generate infeasible network architectures. Compounding this infeasibility issue is that the fitness function involves calculating the all-terminal reliability of the network, a calculation which is computationally expensive. Therefore, it is imperative that the search balances the need to thoroughly explore the boundary between feasible and infeasible networks, along with calculating fitness on only the most promising candidate networks. The algorithm results are compared to optimum results found by branch and bound and also to GA results without local search operators on a suite of 79 test problems. This GA strategy of employing bounds, simple heuristic checks and problem specific repair and local search operators can be used on other highly constrained combinatorial applications where numerous fitness calculations are prohibitive.
20370847
A Set Probability Technique for Detecting Relative Time Order Across Multiple Neurons
With the development of multielectrode recording techniques, it is possible to measure the cell firing patterns of multiple neurons simultaneously, generating a large quantity of data. Identification of the firing patterns within these large groups of cells is an important and a challenging problem in data analysis. Here, we consider the problem of measuring the significance of a repeat in the cell firing sequence across arbitrary numbers of cells. In particular, we consider the question, given a ranked order of cells numbered 1 to N, what is the probability that another sequence of length n contains j consecutive increasing elements? Assuming each element of the sequence is drawn with replacement from the numbers 1 through N, we derive a recursive formula for the probability of the sequence of length j or more. For n < 2j, a closed-form solution is derived. For n 2j, we obtain upper and lower bounds for these probabilities for various combinations of parameter values. These can be computed very quickly. For a typical case with small N (<10) and large n (<3000), sequences of 7 and 8 are statistically very unlikely. A potential application of this technique is in the detection of repeats in hippocampal place cell order during sleep. Unlike most previous articles on increasing runs in random lists, we use a probability approach based on sets of overlapping sequences.
39614676
Branch Target Buffer Design and Optimization
A branch target buffer (BTB) can reduce the performance penalty of branches in pipelined processors by predicting the path of the branch and caching information used by the branch. Two major issues in the design of BTBs that achieves maximum performance with a limited number of bits allocated to the BTB implementation are discussed. The first is BTB management. A method for discarding branches from the BTB is examined. This method discards the branch with the smallest expected value for improving performance; it outperforms the least recently used (LRU) strategy by a small margin, at the cost of additional complexity. The second issue is the question of what information to store in the BTB. A BTB entry can consist of one or more of the following: branch tag, prediction information, the branch target address, and instructions at the branch target. Various BTB designs, with one or more of these fields, are evaluated and compared. >