Concurrent Knowledge Extraction in Public-Key Models

Knowledge extraction is a fundamental notion, modeling machine possession of values (witnesses) in a computational complexity sense and enabling one to argue about the internal state of a party in a protocol without probing its internal secret state. However, when transactions are concurrent, say over the Internet, with players possessing public keys (as is common in cryptography), assuring that entities “know” what they claim to know, where adversaries may be well coordinated across different transactions, turns out to be much more subtle and in need of re-examination. In such settings, mixing the public-key structure as part of the language and statements is a natural adversarial strategy. Here, we investigate how to formally treat knowledge possession by parties interacting concurrently in the public-key model. More technically, we look into the relative power of the notion of “concurrent knowledge extraction” (CKE) for concurrent zero knowledge (CZK) in the bare public-key (BPK) model, where the language and statements being proved can be dynamically and adaptively chosen by the prover and may be possibly based on verifiers’ public keys. By concrete attacks against some existing natural protocols, we first show that concurrent soundness and normal arguments of knowledge do not guarantee concurrent verifier security in the public-key setting. Here, roughly speaking, concurrent verifier security says that the malicious concurrent prover should “know" all the witnesses to all the possibly public-key-related statements adaptively chosen and successfully proved in the concurrent sessions. These concrete attacks serve as a good motivation for understanding “possession of knowledge” for concurrent transactions with registered public keys, i.e., the subtleties of concurrent knowledge extraction in the public-key model. This motivates us to introduce and formalize the notion of CKE, along with clarifications of various subtleties. Two implementations are then presented for constant-round concurrently knowledge extractable concurrent zero-knowledge (CZK–CKE) argument for \(\mathcal {NP}\) in the BPK model: One protocol is generic and based on standard polynomial-time assumptions, whereas the other protocol is computationally efficient and employs complexity leveraging in a novel way. Both protocols can be practically instantiated for some specific number-theoretic languages without going through general \(\mathcal {NP}\)-reductions. Of independent interest are the discussions about the subtleties surrounding the fundamental structure of Feige–Shamir zero knowledge in the BPK model.     

Efficient Internet traffic delivery over wireless networks

The high demand for wireless Internet connectivity has driven the development of highly efficient radio link technologies. However, their performance can be compromised by inadvertent interactions with the higher-layer TCP flow control protocol. Maximizing the performance of wireless links requires that mechanisms operating at every layer of the protocol stack interact efficiently. This article provides a brief tutorial of some of these radio link enhancements. It then outlines how higher-layer flow control protocols should behave, and provides techniques for taming the behavior of TCP, to ensure that the performance of lower-layer enhancements is not compromised.     

An Adaptive Generalized Transmission Protocol for Ad Hoc Networks

Wireless networking and group communication in combination allows groups of dispersed mobile users to collaborate. This paper presents AGENT, a medium access control (MAC) protocol that unifies point-to-point and multi-point transmission services to facilitate group communication in ad hoc networks. Analysis and experiments performed in a simulated ad hoc network demonstrate that AGENT exhibits reliable and stable performance with high spatial bandwidth reuse. Moreover, variation in the proportion of point-to-point and multi-point traffic is shown to have little impact on the overall performance of AGENT. Comparison with the other tested MAC protocols reveals that the performance of AGENT is superior, achieving higher channel utilization and lower access delay.     

液体光阀

在不断增长的液晶显示(LCD)优势中，电润湿的新技术正试图在较好的光线利用和简化制造方面，占据一席之地。     

Determination of total glucosinolates in oilseed rape by X-ray spectrometric analysis for oxidised sulphur (S6+)

A rapid X-ray spectrometric (XRS) method has been developed for the determination of the total glucosinolate content of oilseed rape and other Brassica oilseeds. The method is based on analysis for fully oxidised sulphur (S⁶⁺), which includes half the sulphur (S) in the glucosinolate molecule, and the S in sulphate. Results are highly correlated with glucosinolate content determined by glucose release, a standard method widely used in Australia. The relationship is total glucosinolates = (23·97 S⁶⁺ -9·43) r² = 0·987, where the glucosinolate content is expressed as μmol g^?1 and the S⁶⁺ content in mg g^?1. The relationship is applicable to seed of any glucosinolate content and to meal, and is unaffected by changes in protein sulphur content. The correlation of glucosinolates with S⁶⁺ is shown to be closer than the correlation with total S. The latter correlation forms the basis of the existing XRS method, used within the European Community in recent years. The advantages of S⁶⁺ derive from the linearity of the regression and the elimination of errors caused by variation in protein content. The method should be valuable to the Australian oilseed industry because it allows the rapid screening of breeding lines to ensure low glucosinolate content and the assessment of deliveries for crushing and of meal.     

Multiprocessor Architecture for Rapid EEG Frequency Analysis

A multicomputer array is described that speeds up the processing of spectral representation for the EEG.     

Adsorption of soy oil free fatty acids by rice hull ash

Studies demonstrated that free fatty acids can be adsorbed from a soybean oil/hexane miscella by inorganic rice hull ash. A 1% dose was effective in diminishing free fatty acid concentrations but acid activation reduced the adsorption. Binding of free fatty acids followed a Freundlich isotherm with smaller doses of ash adsorbing more efficiently. Addition of isopropanol to the miscella promoted the adsorption, while water deactivation of the ash had no effect, possibly because water occupied sites not accessible to free fatty acids. Impaired adsorption behavior of ash heated above 700°C could have been due to disruption of the crystal form. The adsorption behavior of rice hull ash may be more fully understood with a better knowledge of adsorbent structure.     

The photoelectrochemical reduction of pyrene in acetonitrile solution

The reduction of pyrene (Py) at a mercury channel electrode is studied in acetonitrile solution, both in the dark and under conditions where the pyrene radical anion (Py^−.) is photoexcited, using a wavelength of 501.7 nm. In the dark a reversible one-electron process occurs forming the radical anion. However, upon photoexcitation of the electrogenerated radical anion, photocurrents are observed, and the precise electrode mechanism is shown to be: The photocurrent arising from further reduction of Py, since rapid homogeneous reactions of Py⁻² give electroinactive products. With this scheme an “effective” second order decay of Py^−√ is observed, RATE = −k_eff[Py^−√]^p2 where k_eff is proportional to k₃ I/k_f. k_eff has been evaluated from analysis of the limiting current-flow rate behaviour at the channel electrode at the channel electrode. This was found to be 4.0 ± 0.1 × 10³ mol−1 dm³ s⁻¹ at a light intensity of 0.30 W cm⁻² and a pyrene concentyration of 2.97 mM.     

Nitrous oxide emissions from two sites in Southern England during winter 1981/1982

Nitrous oxide fluxes from soil surfaces were measured during winter 1981/82 on two fallow sites, a loamy sand and a clay loam, that had been watered to field capacity and fertilised at the rate of 200 kg N ha^?1 on the 5 October 1981. Highest fluxes were obtained in the sampling period immediately after fertiliser application. They were in the range 3.5–20 g N₂O? N ha^?1 day^?1 on the loamy sand, and declined rapidly from a peak of almost 165 g N₂O? N ha^?1 day^?1 on the day following fertiliser application on the clay loam. The temperature during this period was in the range 6.5 to 14°C. As soil temperature declined during the sampling periods in December (?2 to 3°C) and February (4.5 to 6.5°C) and nitrate was leached in the subsoil, N₂O evolution became very low (<1 g N₂O? N ha^?1 day^?1). Rainfall over the whole sampling period from early October to mid-February was 282 mm. On both sites there was a very high degree of variability within the sites at any sampling time.