Computationally Data-Independent Memory Hard Functions

Memory hard functions (MHFs) are an important cryptographic primitive that are used to design egalitarian proofs of work and in the construction of moderately expensive key-derivation functions resistant to brute-force attacks. Broadly speaking, MHFs can be divided into two categories: data-dependent memory hard functions (dMHFs) and data-independent memory hard functions (iMHFs). iMHFs are resistant to certain side-channel attacks as the memory access pattern induced by the honest evaluation algorithm is independent of the potentially sensitive input e.g., password. While dMHFs are potentially vulnerable to side-channel attacks (the induced memory access pattern might leak useful information to a brute-force attacker), they can achieve higher cumulative memory complexity (CMC) in comparison than an iMHF. In particular, any iMHF that can be evaluated in N steps on a sequential machine has CMC at most ?((N^2 log log N)/log N). By contrast, the dMHF scrypt achieves maximal CMC ?(N^2) - though the CMC of scrypt would be reduced to just ?(N) after a side-channel attack. In this paper, we introduce the notion of computationally data-independent memory hard functions (ciMHFs). Intuitively, we require that memory access pattern induced by the (randomized) ciMHF evaluation algorithm appears to be independent from the standpoint of a computationally bounded eavesdropping attacker - even if the attacker selects the initial input. We then ask whether it is possible to circumvent known upper bound for iMHFs and build a ciMHF with CMC ?(N^2). Surprisingly, we answer the question in the affirmative when the ciMHF evaluation algorithm is executed on a two-tiered memory architecture (RAM/Cache). We introduce the notion of a k-restricted dynamic graph to quantify the continuum between unrestricted dMHFs (k=n) and iMHFs (k=1). For any ? > 0 we show how to construct a k-restricted dynamic graph with k=?(N^(1-?)) that provably achieves maximum cumulative pebbling cost ?(N^2). We can use k-restricted dynamic graphs to build a ciMHF provided that cache is large enough to hold k hash outputs and the dynamic graph satisfies a certain property that we call "amenable to shuffling". In particular, we prove that the induced memory access pattern is indistinguishable to a polynomial time attacker who can monitor the locations of read/write requests to RAM, but not cache. We also show that when k=o(N^(1/log log N))then any k-restricted graph with constant indegree has cumulative pebbling cost o(N^2). Our results almost completely characterize the spectrum of k-restricted dynamic graphs

Resilient behaviour of hot mixed and crack sealed asphalt concrete under repeated loading

Bituminous mixes are becoming increasingly important in the road industry. The road engineers identify rutting as a major source of distress in Hot Mix Asphalt (HMA) pavements. The Asphalt Mix Design Marshal method adequately addresses the aggregate and asphalt binder properties that contribute to permanent deformation. However, there is no laboratory test currently at hand to quickly predict permanent deformation susceptibility of HMA. The main purpose of this paper is to provide practical information of laboratory samples for practitioners and mix designers. Thus, relevant test procedures and results of tests conducted are reported in this paper. Two resilient behaviours of cracked sealed asphalt concrete were studied by varying temperature and time of loading to understand the crack sealed pavement behaviour under Iran conditions. Karšto ir supleišėjusio asfaltbetonio tamprumas veikiant kartotinei apkrovai Santrauka Bitumo mišiniai tampa vis svarbesni kelių statyboje. Kelių tiesėjai nustatė, jog didžiausia problema yra provėžos karštoje kelio dangoje. Asfalto mišinio užpildų ir rišamosios medžiagos savybių įtaką ilgalaikėms deformacijoms tiksliai vertina Maršalo metodas, tačiau šiuo metu nėra jokio laboratorinio testo, kuris operatyviai nustatytų ilgalaikes karšto betono mišinio deformacines savybes. Pagrindinis šio straipsnio tikslas – suteikti informaciją apie laboratorinius bandinius mišinių gamintojams ir kelininkams. Taigi čia aprašyti atlikti testai ir gauti rezultatai. Bitumo kiekio mišinyje ir temperatūros įtakos ilgalaikėms asfalto dangos deformacijoms tirti panaudota laboratorinė įranga. Bandant suvokti supleišėjusios dangos elgseną Irano sąlygomis, nagrinėtos dvi supleišėjusio asfaltbetonio tamprumo charakteristikos, keičiant temperatūrą ir apkrovimo trukmę. First Published Online: 21 Oct 2010 Reikšminiai žodžiai: ilgalaikė deformacija, Maršalo metodas, karšto asfalto mišinys, provėžos, įtempis, pleišėjimas

Memory-Hard Puzzles in the Standard Model with Applications to Memory-Hard Functions and Resource-Bounded Locally Decodable Codes

We formally introduce, define, and construct memory-hard puzzles. Intuitively, for a difficulty parameter $t$, a cryptographic puzzle is memory-hard if any parallel random access machine (PRAM) algorithm with small cumulative memory complexity ($\ll t^2$) cannot solve the puzzle; moreover, such puzzles should be both easy to generate and be solvable by a sequential RAM algorithm running in time $t$. Our definitions and constructions of memory-hard puzzles are in the standard model, assuming the existence of indistinguishability obfuscation ($i\mathcal{O}$) and one-way functions (OWFs), and additionally assuming the existence of a memory-hard language. Intuitively, a language is memory-hard if it is undecidable by any PRAM algorithm with small cumulative memory complexity, while a sequential RAM algorithm running in time $t$ can decide the language. Our definitions and constructions of memory-hard objects are the first such definitions and constructions in the standard model without relying on idealized assumptions (such as random oracles). We give two applications which highlight the utility of memory-hard puzzles. For our first application, we give a construction of a (one-time) memory-hard function (MHF) in the standard model, using memory-hard puzzles and additionally assuming $i\mathcal{O}$ and OWFs. For our second application, we show any cryptographic puzzle (e.g., memory-hard, time-lock) can be used to construct resource-bounded locally decodable codes (LDCs) in the standard model, answering an open question of Blocki, Kulkarni, and Zhou (ITC 2020). Resource-bounded LDCs achieve better rate and locality than their classical counterparts under the assumption that the adversarial channel is resource bounded (e.g., a low-depth circuit). Prior constructions of MHFs and resource-bounded LDCs required idealized primitives like random oracles

An Attribute-Based Anonymous Broadcast Encryption Scheme with Adaptive Security in the Standard Model

In broadcast encryption schemes, a distribution center broadcasts an encrypted message to a subset $S$ chosen from a universe of receivers and only the intended users are able to decrypt the message. Most broadcast encryption schemes do not provide anonymity and the identities of target receivers are sent in plaintext. However, in several applications, the authorized users\u27 identities has the same sensitivity as the message itself. YRL, is an anonymous attribute-based broadcast encryption scheme with linear computation, communication and storage overheads in the number of attributes. In this paper, we first propose an attack on the YRL scheme and show that unfortunately the unauthorized receivers can also decrypt the broadcasted message. Next, we propose the Improved-YRL scheme and prove that it achieves anonymity and semantic security under adaptive corruptions in the chosen ciphertext setting. The proof is provided using the dual system encryption technique and is based on three complexity assumptions in composite order bilinear maps. The Improved-YRL scheme is a step forward in solving the long-standing problem of secure and low overhead anonymous broadcast encryption

Bioassay Screening of the Essential Oil and Various Extracts of Fruits of Heracleum persicum Desf. and Rhizomes of Zingiber officinale Rosc. using Brine Shrimp Cytotoxicity Assay

In the present work, the bioassay screening of the essential oil and various extracts of two plants including fruits of Heracleum persicum Desf. and rhizomes of Zingiber officinale Rosc. have been studied with brine shrimp test. There is only one report about cytotoxicity of H. sphondylium in literature and so H. persicum has been used as second selection. At first essentials oil and various extracts of two plants including petroleum ether, chloroform, methanol, ether and aqueous were provided. Then, different concentrations of them were prepared. These fractions were evaluated for toxicity using Brine Shrimp Lethality assay (BSL). Each of fractions was assessed by two methods of disk and solution. Survivors were counted after 24 h. These data were processed in Probit-analysis program to estimate LC50 values (the concentration at which 50% lethality was observed) with 95% confidence intervals for statistically significant comparisons of potencies. In disc method, methanol extract of Z. officinale (LC50=28.3134 μg/ml) showed the most activity in comparison with positive standard of potassium dichromate (LC50=23.2893 μg/ml); but in solution method, essential oil of H. persicum ( LC50=0.0071 μl/ml) was the most active fraction in comparison with potassium dichromate (LC50=27.7528 μg/ml). Totally, among tested fractions, essential oil of the H. persicum has been exhibited the most cytotoxicity. The essential oil of H. persicum was analyzed by GC-MS. The major constituents were hexyl butyrate and octyl acetate

BIOASSAY SCREENING OF THE ESSENTIAL OIL AND VARIOUS EXTRACTS FROM 4 SPICES MEDICINAL PLANTS

Four commonly used spices plants in Iran were evaluated for cytotoxicity effect using Brine Shrimp Lethality (BSL) assay. Essential oils and various extracts of Heracleum persicum, Nigella arvensis, Cinnamomum zeylanicum and Zingiber officinale were assessed by two methods of disk and solution of BSL. Data were processed in probit-analysis program to estimate LC50 values. All of the tested fractions have exhibited more cytotoxicity in the solution method. Essential oils of H. persicum and C. zeylanicum have shown the most cytotoxicity with LC50 values 0.007 and 0.03 μg/ml respectively. None of aqueous extracts showed significant cytotoxicity. The analysis of the essential oil of H. persicum showed the hexyl butyrate and octyl acetate as the main compounds. These results suggest some limitation for using of these spices in diet. Furthermore, these plants could be considered as a source of cytotoxic compounds which might be studied in more details

Indoor environment assessment of special wards of educational hospitals for the detection of fungal contamination sources: A multi-center study (2019-2021)

Background and Purpose: The hospital environment was reported as a real habitat for different microorganisms, especially mold fungi. On the other hand, these opportunistic fungi were considered hospital-acquired mold infections in patients with weak immune status. Therefore, this multi-center study aimed to evaluate 23 hospitals in 18 provinces of Iran for fungal contamination sources.Materials and Methods: In total, 43 opened Petri plates and 213 surface samples were collected throughout different wards of 23 hospitals. All collected samples were inoculated into Sabouraud Dextrose Agar containing Chloramphenicol (SC), and the plates were then incubated at 27-30ºC for 7-14 days.Results: A total of 210 fungal colonies from equipment (162, 77.1%) and air (48,22.9%) were identified. The most predominant isolated genus was Aspergillus (47.5%),followed by Rhizopus (14.2%), Mucor (11.7%), and Cladosporium (9.2%). Aspergillus(39.5%), Cladosporium (16.6%), as well as Penicillium and Sterile hyphae (10.4% each), were the most isolates from the air samples. Moreover, intensive care units (38.5%) and operating rooms (21.9%) had the highest number of isolated fungal colonies. Out of 256 collected samples from equipment and air, 163 (63.7%) were positive for fungal growth.The rate of fungal contamination in instrument and air samples was 128/213 (60.1%) and 35/43 (81.2%), respectively. Among the isolated species of Aspergillus, A. flavus complex (38/96, 39.6%), A. niger complex (31/96, 32.3%), and A. fumigatus complex (15/96, 15.6%) were the commonest species.Conclusion: According to our findings, in addition to air, equipment and instrument should be considered among the significant sources of fungal contamination in the indoor environment of hospitals. Airborne fungi, Hospital, Indoor air, Equipment, Sources of fungal contamination in the indoor environment of hospitals