Sustained Space and Cumulative Complexity Trade-offs for Data-Dependent Memory-Hard Functions

Memory-hard functions (MHFs) are a useful cryptographic primitive which can be used to design egalitarian proof of work puzzles and to protect low entropy secrets like passwords against brute-force attackers. Intuitively, a memory-hard function is a function whose evaluation costs are dominated by memory costs even if the attacker uses specialized hardware (FPGAs/ASICs), and several cost metrics have been proposed to quantify this intuition. For example, space-time cost looks at the product of running time and the maximum space usage over the entire execution of an algorithm. Alwen and Serbinenko (STOC 2015) observed that the space-time cost of evaluating a function multiple times may not scale linearly in the number of instances being evaluated and introduced the stricter requirement that a memory-hard function has high cumulative memory complexity (CMC) to ensure that an attacker\u27s amortized space-time costs remain large even if the attacker evaluates the function on multiple different inputs in parallel. Alwen et al. (EUROCRYPT 2018) observed that the notion of CMC still gives the attacker undesirable flexibility in selecting space-time tradeoffs e.g., while the MHF scrypt has maximal CMC $\Omega(N^2)$, an attacker could evaluate the function with constant $O(1)$ memory in time $O(N^2)$. Alwen et al. introduced an even stricter notion of Sustained Space complexity and designed an MHF which has $s=\Omega(N/\log N)$ sustained complexity $t=\Omega(N)$ i.e., any algorithm evaluating the function in the parallel random oracle model must have at least $t=\Omega(N)$ steps where the memory usage is at least $\Omega(N/\log N)$. In this work, we use dynamic pebbling games and dynamic graphs to explore tradeoffs between sustained space complexity and cumulative memory complexity for data-dependent memory-hard functions such as Argon2id and scrypt. We design our own dynamic graph (dMHF) with the property that {\em any} dynamic pebbling strategy either (1) has $\Omega(N)$ rounds with $\Omega(N)$ space, or (2) has CMC $\Omega(N^{3-\epsilon})$ --- substantially larger than $N^2$. For Argon2id we show that {\em any} dynamic pebbling strategy either(1) has $\Omega(N)$ rounds with $\Omega(N^{1-\epsilon})$ space, or (2) has CMC $\omega(N^2)$. We also present a dynamic version of DRSample (Alwen et al. 2017) for which {\em any} dynamic pebbling strategy either (1) has $\Omega(N)$ rounds with $\Omega(N/\log N)$ space, or (2) has CMC $\Omega(N^3/\log N)$

The Parallel Reversible Pebbling Game: Analyzing the Post-Quantum Security of iMHFs

The classical (parallel) black pebbling game is a useful abstraction which allows us to analyze the resources (space, space-time, cumulative space) necessary to evaluate a function $f$ with a static data-dependency graph $G$. Of particular interest in the field of cryptography are data-independent memory-hard functions $f_{G,H}$ which are defined by a directed acyclic graph (DAG) $G$ and a cryptographic hash function $H$. The pebbling complexity of the graph $G$ characterizes the amortized cost of evaluating $f_{G,H}$ multiple times as well as the total cost to run a brute-force preimage attack over a fixed domain $\mathcal{X}$, i.e., given $y \in \{0,1\}^*$ find $x \in \mathcal{X}$ such that $f_{G,H}(x)=y$. While a classical attacker will need to evaluate the function $f_{G,H}$ at least $m=|\mathcal{X}|$ times a quantum attacker running Grover\u27s algorithm only requires $\mathcal{O}(\sqrt{m})$ blackbox calls to a quantum circuit $C_{G,H}$ evaluating the function $f_{G,H}$. Thus, to analyze the cost of a quantum attack it is crucial to understand the space-time cost (equivalently width times depth) of the quantum circuit $C_{G,H}$. We first observe that a legal black pebbling strategy for the graph $G$ does not necessarily imply the existence of a quantum circuit with comparable complexity --- in contrast to the classical setting where any efficient pebbling strategy for $G$ corresponds to an algorithm with comparable complexity for evaluating $f_{G,H}$. Motivated by this observation we introduce a new parallel reversible pebbling game which captures additional restrictions imposed by the No-Deletion Theorem in Quantum Computing. We apply our new reversible pebbling game to analyze the reversible space-time complexity of several important graphs: Line Graphs, Argon2i-A, Argon2i-B, and DRSample. Specifically, (1) we show that a line graph of size $N$ has reversible space-time complexity at most $\mathcal{O}\left(N^{1+\frac{2}{\sqrt{\log N}}}\right)$. (2) We show that any $(e,d)$-reducible DAG has reversible space-time complexity at most $\mathcal{O}(Ne+dN2^d)$. In particular, this implies that the reversible space-time complexity of Argon2i-A and Argon2i-B are at most $\mathcal{O}(N^2 \log \log N/\sqrt{\log N})$ and $\mathcal{O}(N^2/\sqrt[3]{\log N})$, respectively. (3) We show that the reversible space-time complexity of DRSample is at most $\mathcal{O}(N^2 \log \log N/\log N)$. We also study the cumulative pebbling cost of reversible pebblings extending a (non-reversible) pebbling attack of Alwen and Blocki on depth-reducible graphs

Evaluación de dosis de fertilizantes foliar y edáfico en el crecimiento y rendimiento del cultivo de chiltoma (Capsicum annuum L.) var Nathalie, San Esteban #2, Jinotega, 2021

En Nicaragua se cultivan diferentes tipos de cultivos para el consumo nacional, entre ellos granos básicos, legumbres y hortalizas; pero en los últimos veinte años está pasando por un problema de interés mundial como es el cambio climático, ya que este afecta la producción de muchos rubros. Al igual que estos cultivos, la chiltoma (Capsicum annuum L.) es de gran importancia en el sector de comercialización debido a la demanda por su consumo. No obstante, la producción de chiltoma presenta problemas, tales como el manejo de plagas, fertilización, riego, variedades. Considerando lo anterior, el presente estudio se desarrolló durante el año 2021 sobre un Diseño Jerárquico con repeticiones, y tuvo como propósito la valoración de fertilizantes (tres dosis de fertilizante foliar, tres dosis fertilizantes edáfico y tres dosis de Foliar + Edáfico) en la variedad Nathalie, en la comunidad de San Esteban # 2, departamento de Jinotega. Las variables de crecimiento y de rendimiento fueron objeto de un Análisis de Varianza (ANDEVA) y categorización estadística (Duncan y T, ∞=0.05). El fertilizante foliar (Foltron: N, P2O5, K2O, Fe, Zn, Giberelinas, Ácidos húmicos, Mg, Mn, B, Cu, Mo, Folcistenina y Agua) mostró efecto en variables de crecimiento y el rendimiento. Asimismo, con la aplicación de Foltron se obtuvieron promedios de 33 590 kg ha-1 a 40 014 kg ha-1, en cambio con el fertilizante edáfico produjo rendimientos entre 31 643 kg ha-1 y 36 214 kg ha-1. La combinación de ambos fertilizantes presentó los bajos rendimientos. Por otro lado, mediante el análisis Beneficio/Costo (B/C), los resultados indican que Foltron mostró los mayores valores de B/C con $5 587.47, y la mejor relación Beneficio Costo con$ 1.172, en comparación a los otros tratamientos

Characterizing Transiting Extrasolar Planets with Narrow-Band Photometry and GTC/OSIRIS

We report the first extrasolar planet observations from the 10.4-m Gran Telescopio Canarias (GTC), currently the world's largest, fully steerable, single-aperture optical telescope. We used the OSIRIS tunable filter imager on the GTC to acquire high-precision, narrow-band photometry of the transits of the giant exoplanets, TrES-2b and TrES-3b. We obtained near-simultaneous observations in two near-infrared (NIR) wavebands (790.2 and 794.4 +/- 2.0 nm) specifically chosen to avoid water vapor absorption and skyglow so as to minimize the atmospheric effects that often limit the precision of ground-based photometry. Our results demonstrate a very-high photometric precision with minimal atmospheric contamination despite relatively poor atmospheric conditions and some technical problems with the telescope. We find the photometric precision for the TrES-2 observations to be 0.343 and 0.412 mmag for the 790.2 and 794.4 nm light curves, and the precision of the TrES-3 observations was found to be 0.470 and 0.424 mmag for the 790.2 and 794.4 nm light curves. We also discuss how future follow-up observations of transiting planets with this novel technique can contribute to the characterization of Neptune- and super-Earth-size planets to be discovered by space-based missions like CoRoT and Kepler, as well as measure atmospheric properties of giant planets, such as the strength of atmospheric absorption features.Comment: 9 pages, including 3 figures and 2 tables; accepted for publication in MNRA

Full Statistical Mediation of the Relationship Between Trauma and Depressive Symptoms

Owing to the potentially devastating effects of trauma‐induced depression, explaining the relationship between trauma and depressive symptoms is important. In this study, we measured lifelong exposure to potentially traumatic events and depressive symptoms in 370‐female undergraduates. We also measured anxiety, past negative time perspective and dissociation as potential mediators. Trauma exposure and depressive symptoms were related with a small but significant effect size (r = .16). Trauma was not associated with dissociation. We found that past negative time perspective and anxiety were full statistical mediators of this trauma‐depressive symptoms relationship. These two mediators combined accounted for all of the variance in that association. Anxiety accounted for more of the variance than past negative time perspective. A proposed explanation is that trauma both affectively elevates anxiety and cognitively creates an enduring focus on the events. Chronic anxiety and a past negative time perspective may lead to depression over time. The clinical implications are possible explanations as to why some treatments work

Are current dynamic water quality models too complex? A comparison of a new parsimonious phosphorus model, SimplyP, and INCA-P

Catchment-scale water quality models are becoming increasingly popular tools for exploring the potential effects of land management, land use change and climate change on water quality. However, the dynamic, catchment-scale nutrient models in common usage are complex, with many uncertain parameters requiring calibration, limiting their usability and robustness. A key question is whether this complexity is justified. To explore this, we have developed a parsimonious P model, SimplyP, incorporating a coupled rainfall-runoff model and a biogeochemical model able to simulate streamflow, suspended sediment, particulate and dissolved P dynamics. The model’s complexity is compared in a small rural catchment in northeast Scotland. For three land use classes, less than six SimplyP model parameters must be determined through calibration alone, the rest may be based on measurements; INCA-P has around 40 unmeasurable parameters. Despite simpler process-representation, SimplyP produced a slightly better dissolved P simulation during both calibration and validation, and produced similar long-term projections in response to changes in land management. Results support the hypothesis that INCA-P is overly complex for the study catchment. We hope our findings will help prompt wider model comparison exercises, as well as debate amongst the water quality modelling community as to whether today's models are fit for purpose. Simpler models such as SimplyP have the potential to be useful management and research tools, building blocks for future model development (prototype code is freely available), or benchmarks against which more complex models could be evaluated

SPECULOOS exoplanet search and its prototype on TRAPPIST

One of the most significant goals of modern science is establishing whether life exists around other suns. The most direct path towards its achievement is the detection and atmospheric characterization of terrestrial exoplanets with potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs), i.e. very-low-mass stars and brown dwarfs with effective temperatures lower than 2700 K, represent a unique opportunity to reach this goal within the next decade. The potential of the transit method for detecting potentially habitable Earth-sized planets around these objects is drastically increased compared to Earth-Sun analogs. Furthermore, only a terrestrial planet transiting a nearby UCD would be amenable for a thorough atmospheric characterization, including the search for possible biosignatures, with near-future facilities such as the James Webb Space Telescope. In this chapter, we first describe the physical properties of UCDs as well as the unique potential they offer for the detection of potentially habitable Earth-sized planets suitable for atmospheric characterization. Then, we present the SPECULOOS ground-based transit survey, that will search for Earth-sized planets transiting the nearest UCDs, as well as its prototype survey on the TRAPPIST telescopes. We conclude by discussing the prospects offered by the recent detection by this prototype survey of a system of seven temperate Earth-sized planets transiting a nearby UCD, TRAPPIST-1.Comment: Submitted as a chapter in the "Handbook of Exoplanets" (editors: H. Deeg & J.A. Belmonte; Section Editor: N. Narita). 16 pages, 4 figure

Three New Coordination Compounds with Push-Pull Ligand p

International audienceFrom ethanolic solutions containing p-aminobenzonitrile (4ABN) and the respective metal salt three new coordination compounds were obtained and their crystal structures solved and refined from X-ray single-crystal diffraction data: [Ag(4ABN)4/2]BF4 (P 21/n, Z = 4) (1), [Cu(4ABN)4/2(H2O)2](NO3)2 x 2 H2O (P -1, Z = 2) (2) and [Co(4ABN)2(H2O)2Cl2] (P 21/n, Z = 2) (3). 1 is a coordination polymer with a distorted tetrahedral AgN4 coordination and layered polymeric [Ag(4ABN)4] cations, which are held together by van der Waals interactions. It represents the first homoleptic complex of 4ABN. In 2 Jahn-Teller distorted CuN4O2 octahedra are connected to polymeric chain-like [Cu(4ABN)4/2(H2O)2] cations, which are interconnected by hydrogen bonds including further water molecules and NO3- anions. 3 is a complex with an octahedral CoCl2N2O2 coordination. In the solid state structure, they are held together by N-H...Cl hydrogen bonds