Measuring the Effects of Thread Placement on the Kendall Square KSR1

This paper describes a measurement study of the effects of thread placement on memory access times on the Kendall Square multiprocessor, the KSRl. The KSRl uses a conventional shared memory programming model in a distributed memory architecture. The architecture is based on a ring of rings of 64-bit superscalar microprocessors. The KSRl has a Cache-Only Memory Architecture (COMA). Memory consists of the local cache memoria attached to each processor. Whenever an address is accessed, the data item is automatically copied to the local cache memory module, 80 that access times for subsequent references will be minimal. If a local cache has space allocated for a particular data item, but does not have a current valid copy of that data item, then it is possible for the cache to acquire a valid read-only copy before it is requested by the local processor due to a request by a different processor that happens to pass by on the ring. This automatic prefetching can greatly reduce the average time for a thread to acquire data items. Because of the automatic prefetching, the time required to obtain a valid copy of a data item does not depend simply on the distance from the owner of the data item, but also depends on the placement and number of other processing threads which ehare the same data item. Also, the strategic placement of processing threads helps programs take advantage of the unique features of the memory architecture which help eliminate memory access bottlenecks for shared data sets. Experiments run on the KSRl across a wide variety of thread configurations show that shared memory access is accelerated through strategic placement of threads which share data. The results indicate strategies for improving the performance of applications programs, and illustrate that KSRl memory access times can remain nearly constant even when the number of participating threads increases

Identification of Bioactive Compound From Microalga BTM 11 as Hepatitis C Virus RNA Helicase Inhibitor

Hepatitis C virus (HCV) is the major causative agent of chronic liver disease. Recently, the inhibition of NS3 RNA helicase/ATPase activity is being explored as the specifically targeted antiviral therapy (STAT) against HCV infection. This study was aimed to elucidate potential candidates for anti-HCV therapy derived from Indonesian indigenous microalgae. The microalga designated as BTM 11 was isolated and cultured. Methanol extract of BTM 11 was screened as the opponent of purified HCV NS3 RNA helicase enzyme through colorimetric ATPase assay. Screening of chemical compound and fractionation by using gel filtration chromatography with eluent of methanol : chloroform (1:99) were conducted for identification and isolation of the bioactive compounds. The third fraction of fractionated sample showed a relatively strong ATPase inhibitory effect (81.23 ± 2.25 %) compared to the negative control. Further analysis of third fraction using thin layer chromatography (TLC) with eluent of chloroform : methanol (9:2) gave two spots with the Rf value of 0.8 and 0.37, respectively. In addition, high performance liquid chromatography (HPLC) analysis showed absorption peak with the highest abundance at the retention time of 12.483 and 16.617 minutes which absorbed at 266 and 230 nm wavelenght, respectively. According to those analyses, this study suggests that bioactive compounds derived from BTM 11 were classified as the groups of flavonoids and feasible as potential candidates for anti-HCV therapy through the inhibitory effect of NS3 RNA helicase/ATPase activity

Extended Functionality in Verifiable Searchable Encryption

Abstract. When outsourcing the storage of sensitive data to an (un-trusted) remote server, a data owner may choose to encrypt the data beforehand to preserve confidentiality. However, it is then difficult to efficiently retrieve specific portions of the data as the server is unable to identify the relevant information. Searchable encryption has been well studied as a solution to this problem, allowing data owners and other au-thorised users to generate search queries which the server may execute over the encrypted data to identify relevant data portions. However, many current schemes lack two important properties: verifia-bility of search results, and expressive queries. We introduce Extended Verifiable Searchable Encryption (eVSE) that permits a user to verify that search results are correct and complete. We also permit verifiabl

Sub-logarithmic Distributed Oblivious RAM with Small Block Size

Oblivious RAM (ORAM) is a cryptographic primitive that allows a client to securely execute RAM programs over data that is stored in an untrusted server. Distributed Oblivious RAM is a variant of ORAM, where the data is stored in $m>1$ servers. Extensive research over the last few decades have succeeded to reduce the bandwidth overhead of ORAM schemes, both in the single-server and the multi-server setting, from $O(\sqrt{N})$ to $O(1)$. However, all known protocols that achieve a sub-logarithmic overhead either require heavy server-side computation (e.g. homomorphic encryption), or a large block size of at least $\Omega(\log^3 N)$. In this paper, we present a family of distributed ORAM constructions that follow the hierarchical approach of Goldreich and Ostrovsky [GO96]. We enhance known techniques, and develop new ones, to take better advantage of the existence of multiple servers. By plugging efficient known hashing schemes in our constructions, we get the following results: 1. For any $m\geq 2$, we show an $m$-server ORAM scheme with $O(\log N/\log\log N)$ overhead, and block size $\Omega(\log^2 N)$. This scheme is private even against an $(m-1)$-server collusion. 2. A 3-server ORAM construction with $O(\omega(1)\log N/\log\log N)$ overhead and a block size almost logarithmic, i.e. $\Omega(\log^{1+\epsilon}N)$. We also investigate a model where the servers are allowed to perform a linear amount of light local computations, and show that constant overhead is achievable in this model, through a simple four-server ORAM protocol

Perfectly Secure Oblivious RAM with Sublinear Bandwidth Overhead

Oblivious RAM (ORAM) has established itself as a fundamental cryptographic building block. Understanding which bandwidth overheads are possible under which assumptions has been the topic of a vast amount of previous works. In this work, we focus on perfectly secure ORAM and we present the first construction with sublinear bandwidth overhead in the worst-case. All prior constructions with perfect security require linear communication overhead in the worst-case and only achieve sublinear bandwidth overheads in the amortized sense. We present a fundamentally new approach for construction ORAM and our results significantly advance our understanding of what is possible with perfect security. Our main construction, Lookahead ORAM, is perfectly secure, has a worst-case bandwidth overhead of $\mathcal{O}(\sqrt{n})$, and a total storage cost of $\mathcal{O}(n)$ on the server-side, where $n$ is the maximum number of stored data elements. In terms of concrete server-side storage costs, our construction has the smallest storage overhead among all perfectly and statistically secure ORAMs and is only a factor 3 worse than the most storage efficient computationally secure ORAM. Assuming a client-side position map, our construction is the first, among all ORAMs with worst-case sublinear overhead, that allows for a $\mathcal{O}(1)$ online bandwidth overhead without server-side computation. Along the way, we construct a conceptually extremely simple statistically secure ORAM with a worst-case bandwidth overhead of $\mathcal{O}(\sqrt{n}\frac{\log{n}}{\log{\log{n}}})$, which may be of independent interest

Fully Deniable Interactive Encryption

Deniable encryption (Canetti et al., Crypto 1996) enhances secret communication over public channels, providing the additional guarantee that the secrecy of communication is protected even if the parties are later coerced (or willingly bribed) to expose their entire internal states: plaintexts, keys and randomness. To date, constructions of deniable encryption --- and more generally, interactive deniable communication --- only address restricted cases where only one party is compromised (Sahai and Waters, STOC 2014). The main question --- whether deniable communication is at all possible if both parties are coerced at once --- has remained open. We resolve this question in the affirmative, presenting a communication protocol that is fully deniable under coercion of both parties. Our scheme has three rounds, assumes subexponentially secure indistinguishability obfuscation and one-way functions, and uses a short global reference string that is generated once at system set-up and suffices for an unbounded number of encryptions and decryptions. Of independent interest, we introduce a new notion called off-the-record deniability, which protects parties even when their claimed internal states are inconsistent (a case not covered by prior definitions). Our scheme satisfies both standard deniability and off-the-record deniability

Simple and Efficient Two-Server ORAM

We show a protocol for two-server oblivious RAM (ORAM) that is simpler and more efficient than the best prior work. Our construction combines any tree-based ORAM with an extension of a two-server private information retrieval scheme by Boyle et al., and is able to avoid recursion and thus use only one round of interaction. In addition, our scheme has a very cheap initialization phase, making it well suited for RAM-based secure computation. Although our scheme requires the servers to perform a linear scan over the entire data, the cryptographic computation involved consists only of block-cipher evaluations. A practical instantiation of our protocol has excellent concrete parameters: for storing an $N$-element array of arbitrary size data blocks with statistical security parameter $\lambda$, the servers each store $4N$ encrypted blocks, the client stores $\lambda+2\log N$ blocks, and the total communication per logical access is roughly $10 \log N$ encrypted blocks

Generic Constructions of Robustly Reusable Fuzzy Extractor

Robustly reusable Fuzzy Extractor (rrFE) considers reusability and robustness simultaneously. We present two approaches to the generic construction of rrFE. Both of approaches make use of a secure sketch and universal hash functions. The first approach also employs a special pseudo-random function (PRF), namely unique-input key-shift (ui-ks) secure PRF, and the second uses a key-shift secure auxiliary-input authenticated encryption (AIAE). The ui-ks security of PRF (resp. key-shift security of AIAE), together with the homomorphic properties of secure sketch and universal hash function, guarantees the reusability and robustness of rrFE. Meanwhile, we show two instantiations of the two approaches respectively. The first instantiation results in the first rrFE from the LWE assumption, while the second instantiation results in the first rrFE from the DDH assumption over non-pairing groups

Robustly Reusable Fuzzy Extractor from Standard Assumptions

A fuzzy extractor (FE) aims at deriving and reproducing (almost) uniform cryptographic keys from noisy non-uniform sources. To reproduce an identical key R from subsequent readings of a noisy source, it is necessary to eliminate the noises from those readings. To this end, a public helper string P, together with the key R, is produced from the first reading of the source during the initial enrollment phase. In this paper, we consider computational fuzzy extractor. We formalize robustly reusable fuzzy extractor (rrFE) which considers reusability and robustness simultaneously in the Common Reference String (CRS) model. Reusability of rrFE deals with source reuse. It guarantees that the key R output by fuzzy extractor is pseudo-random even if the initial enrollment is applied to the same source several times, generating multiple public helper strings and keys (P_i, R_i). Robustness of rrFE deals with active probabilistic polynomial-time adversaries, who may manipulate the public helper string P_i to affect the reproduction of R_i. Any modification of P_i by the adversary will be detected by the robustness of rrFE