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 $k \geq n - t+{\rm log} (\frac {1}{\epsilon})-O(1)$.
10194960
Secure Remote Authentication Using Biometric Data
Biometric data offer a potential source of high-entropy, secret information that can be used in cryptographic protocols provided two issues are addressed: (1) biometric data are not uniformly distributed; and (2) they are not exactly reproducible. Recent work, most notably that of Dodis, Reyzin, and Smith, has shown how these obstacles may be overcome by allowing some auxiliary public information to be reliably sent from a server to the human user. Subsequent work of Boyen has shown how to extend these techniques, in the random oracle model, to enable unidirectional authentication from the user to the server without the assumption of a reliable communication channel. 
 
We show two efficient techniques enabling the use of biometric data to achieve mutual authentication or authenticated key exchange over a completely insecure (i.e., adversarially controlled) channel. In addition to achieving stronger security guarantees than the work of Boyen, we improve upon his solution in a number of other respects: we tolerate a broader class of errors and, in one case, improve upon the parameters of his solution and give a proof of security in the standard model.
5542444
Efficient and Non-interactive Non-malleable Commitment
We present new constructions of non-malleable commitment schemes, in the public parameter model (where a trusted party makes parameters available to all parties), based on the discrete logarithm or RSA assumptions. The main features of our schemes are: they achieve near-optimal communication for arbitrarily-large messages and are noninteractive. Previous schemes either required (several rounds of) interaction or focused on achieving non-malleable commitment based on general assumptions and were thus efficient only when committing to a single bit. Although our main constructions are for the case of perfectly-hiding commitment, we also present a communication-efficient, noninteractive commitment scheme (based on general assumptions) that is perfectly binding.
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.
36108373
Machine Characterization Based on an Abstract High-Level Language Machine
Measurements are presented for a large number of machines ranging from small workstations to supercomputers. The authors combine these measurements into groups of parameters which relate to specific aspects of the machine implementation, and use these groups to provide overall machine characterizations. The authors also define the concept of pershapes, which represent the level of performance of a machine for different types of computation. A metric based on pershapes is introduced that provides a quantitative way of measuring how similar two machines are in terms of their performance distributions. The metric is related to the extent to which pairs of machines have varying relative performance levels depending on which benchmark is used. >
16044004
Intelligent Meaning Creation in a Clumpy World Helps Communication
This article investigates the problem of how language learners decipher what words mean. In many recent models of language evolution, agents are provided with innate meanings a priori and explicitly transfer them to each other as part of the communication process. By contrast, I investigate how successful communication systems can emerge without innate or transferable meanings, and show that this is dependent on the agents developing highly synchronized conceptual systems. I present experiments with various cognitive, communicative, and environmental factors which affect the likelihood of agents achieving meaning synchronization and demonstrate that an intelligent meaning creation strategy in a clumpy world leads to the highest level of meaning similarity between agents.
9985308
Analysis of shared memory misses and reference patterns
Shared bus computer systems permit the relatively simple and efficient implementation of cache consistency algorithms, but the shared bus is a bottleneck which limits performance. False sharing can be an important source of unnecessary traffic for invalidation-based protocols, elimination of which can provide significant performance improvements. For many multiprocessor workloads, however, most misses are true sharing plus cold start misses. Regardless of the cause of cache misses, the largest fraction of bus traffic are words transferred between caches without being accessed, which we refer to as dead sharing. We establish here new methods for characterizing cache block reference patterns, and we measure how these patterns change with variation in workload and block size. Our results show that 42 percent of 64-byte cache blocks are invalidated before more than one word has been read from the block and that 58 percent of blocks that have been modified only have a single word modified before an invalidation to the block occurs. Approximately 50 percent of blocks written and subsequently read by other caches show no use of the newly written information before the block is again invalidated. In addition to our general analysis of reference patterns, we also present a detailed analysis of dead sharing for each shared memory multiprocessor program studied. We find that the worst 10 blocks (based on most total misses) from each of our traces contribute almost 50 percent of the false shearing misses and almost 20 percent of the true sharing misses (on average). A relatively simple restructuring of four of our workloads based on analysis of these 10 worst blocks leads to a 21 percent reduction in overall misses and a 15 percent reduction in execution time. Permitting the block size to vary (as could be accomplished with a sector cache) shows that bus traffic can be reduced by 88 percent (for 64-byte blocks) while also decreasing the miss ratio by 35 percent.
34073205
Genetic Optimization Using A Penalty Function
15250864
Reducing processor power consumption by improving processor time management in a single-user operating system
The CPU is one of the major power consumers in a portable computer, and considerable power can be saved by turning off the CPU when it is not doing useful work. In Apple’s MacOS, however, idle time is often converted to busy waiting, and generally it is very hard to tell when no useful computation is occurring. In this paper, we suggest several heuristic techniques for identifying this condition, and for temporarily putting the CPU in a low-power state. These techniques include turning off the processor when all processes are blocked, turning off the processor when processes appear to be busy waiting, and extending real time process sleep periods. We use trace-driven simulation, using processor run interval traces, to evaluate the potential energy savings and performance impact. We find that these techniques save considerable amounts of processor energy (as much as 66%), while having very little performance impact (less than 2% increase in run time). Implementing the proposed strategies should increase battery lifetime by approximately 20% relative to Apple’s current CPU power management strategy, since the CPU and associated logic are responsible for about 32% of power use; similar techniques should be applicable to operating systems with similar behavior.