CRYSTALS-Dilithium: A lattice-based digital signature scheme

In this paper, we present the lattice-based signature scheme Dilithium, which is a component of the CRYSTALS (Cryptographic Suite for Algebraic Lattices) suite that was submitted to NIST’s call for post-quantum cryptographic standards. The design of the scheme avoids all uses of discrete Gaussian sampling and is easily implementable in constant-time. For the same security levels, our scheme has a public key that is 2.5X smaller than the previously most efficient lattice-based schemes that did not use Gaussians, while having essentially the same signature size. In addition to the new design, we significantly improve the running time of the main component of many lattice-based constructions – the number theoretic transform. Our AVX2-based implementation results in a speed-up of roughly a factor of 2 over the previously best algorithms that appear in the literature. The techniques for obtaining this speed-up also have applications to other lattice-based schemes

CRYSTALS - Kyber: A CCA-secure Module-Lattice-Based KEM

Rapid advances in quantum computing, together with the announcement by the National Institute of Standards and Technology (NIST) to define new standards for digital-signature, encryption, and key-establishment protocols, have created significant interest in post-quantum cryptographic schemes. This paper introduces Kyber (part of CRYSTALS - Cryptographic Suite for Algebraic Lattices - a package submitted to NIST post-quantum standardization effort in November 2017), a portfolio of post-quantum cryptographic primitives built around a key-encapsulation mechanism (KEM), based on hardness assumptions over module lattices. Our KEM is most naturally seen as a successor to the NEWHOPE KEM (Usenix 2016). In particular, the key and ciphertext sizes of our new construction are about half the size, the KEM offers CCA instead of only passive security, the security is based on a more general (and flexible) lattice problem, and our optimized implementation results in essentially the same running time as the aforementioned scheme. We first introduce a CPA-secure public-key encryption scheme, apply a variant of the Fujisaki-Okamoto transform to create a CCA-secure KEM, and eventually construct, in a black-box manner, CCA-secure encryption, key exchange, and authenticated-key-exchange schemes. The security of our primitives is based on the hardness of Module-LWE in the classical and quantum random oracle models, and our concrete parameters conservatively target more than 128 bits of post-quantum security

CRYSTALS - Kyber: A CCA-secure Module-Lattice-Based KEM

Rapid advances in quantum computing, together with the announcement by the National Institute of Standards and Technology (NIST) to define new standards for digitalsignature, encryption, and key-establishment protocols, have created significant interest in post-quantum cryptographic schemes. This paper introduces Kyber (part of CRYSTALS - Cryptographic Suite for Algebraic Lattices - a package submitted to NIST post-quantum standardization effort in November 2017), a portfolio of post-quantum cryptographic primitives built around a key-encapsulation mechanism (KEM), based on hardness assumptions over module lattices. Our KEM is most naturally seen as a successor to the NEWHOPE KEM (Usenix 2016). In particular, the key and ciphertext sizes of our new construction are about half the size, the KEM offers CCA instead of only passive security, the security is based on a more general (and flexible) lattice problem, and our optimized implementation results in essentially the same running time as the aforementioned scheme. We first introduce a CPA-secure public-key encryption scheme, apply a variant of the Fujisaki-Okamoto transform to create a CCA-secure KEM, and eventually construct, in a black-box manner, CCA-secure encryption, key exchange, and authenticated-key-exchange schemes. The security of our primitives is based on the hardness of Module-LWE in the classical and quantum random oracle models, and our concrete parameters conservatively target more than 128 bits of postquantum security

Reconstructing the late-Quaternary glacial history of northeastern Patagonia (43°S, 71°W): new insights from geomorphology, geochronology and numerical glacier modelling

Former investigations conducting geomorphological mapping of Patagonia, a region formerly covered by an extensive ice sheet, have revealed a uniquely rich record of Quaternary glacial sediment-landform assemblages. Patagonia is located in the ocean-dominated southern mid-latitudes and in the pathway of major southern hemisphere circulation systems including the precipitation-bearing southern westerly winds, and the Antarctic circumpolar current. For these reasons, Quaternary glacier reconstructions from Patagonia can help identify the main drivers of climate and glacial events in the Southern Hemisphere. However, in northeastern Patagonia (39-46°S), geochronological data addressing the precise timing of Quaternary glacial events during Pleistocene glacial cycles are lacking. Indeed, in this region, little is known about the magnitude and timing of the Patagonian Ice Sheet’s response to climate events such as, for instance, the local Last Glacial Maximum (lLGM) and the last glacial termination. This Ph.D investigation attempted to fill in this knowledge gap, by producing a robust geochronological reconstruction that would describe the extent, stratigraphic relationship, characteristics and precise timing of most Quaternary glacial events preserved in a key valley system formerly host to major outlet glaciers of the northern Patagonian Ice Sheet. Firstly, this thesis presents the first detailed glacial geomorphological map of the Río Corcovado, Río Huemul and Lago Palena/General Vintter valleys (43°S; 71°W). This mapping effort enabled the identification of 25 distinct categories of sediment-landform assemblages related to the glaciogenic, glaciofluvial and glaciolacustrine activity of the former Patagonian Ice Sheet. This work revealed the preservation of at least eight distinct moraine-outwash complexes at the study site, each indicative of a former outlet-glacier advance/still-stand. Secondly, this thesis provides a new terrestrial cosmogenic nuclide exposure age (n = 38) chronology that establishes the precise timing of the local Last Glacial Maximum resurgences of the Patagonian Ice Sheet. In total, five distinct advances/still-stands of the Río Corcovado outlet glacier occurred over a 6-7 ka period, at 26.4 ± 1.4 ka, 22.4 ± 1.15 ka, 21.7 ± 0.9 ka, 20.7 ± 1.0 ka and 19.9 ± 1.1 ka. Additionally, this work reveals the onset of local deglaciation and the timing of final ice-sheet disintegration occurred at 20-19 ka and 16.3 ± 0.3 ka, respectively. Furthermore, evidences for the likely formation and drainage of three distinct glaciolacustrine phases at the study site were established. Dating revealed that the first phase occurred from 26.4 ± 1.4 ka, the second between ~21 and ~19 ka and the third between ~19 ka and ~16.3 ka. Thirdly, this thesis presents a separate reconstruction of an independent mountain-glacier advance dated to approximately ~18 ka using surface exposure dating. A series of numerical model simulations quantitatively reconstruct the geometry of this late-LGM glacier resurgence, and enable to estimate the local climate conditions at the time. This work for instance suggests that local precipitation must have been significantly higher than today during the late-LGM (~18 ka) glacial event, thus implying an equatorward migration of the Southern Westerly Winds at the time. Finally, this Ph.D. thesis features an additional terrestrial cosmogenic nuclide exposure-age chronology from the study site (n = 25) that focuses on dating the deposition of proglacial outwash plains and moraines formed during three extensive middle Pleistocene expansions of the Patagonian Ice Sheet. This dataset reveals, for the first time, that major glaciations occurred during the marine isotope stage eight and six intervals in northeastern Patagonia, while no prominent advances seem to have occurred during marine isotope stages four and three locally, in contrast with other Patagonian regions. This thesis’s findings enable us to draw hypotheses on the likely paleoclimate forcing mechanisms responsible for the timing of major middle-to-late Pleistocene glaciations at the southern mid-latitudes. This investigation also entails implications for better comprehending whether the former Patagonian Ice Sheet’s different sectors responded to major climate events synchronosuly or asynchronously during the late Quaternary

Impact of viscoelasticity and juvenile wood occurence on the tree reorientation process

The effect of viscoelasticity and juvenile wood on biomechanical performances of a tree in reorientation process was investigated numerically by calculating the up-righting efficiency and flexibility of a titled stem. During a reorientation process, the central part of a tree stem is submitted to high levels of prestresses so that its flexibility drops dramatically. Two factors influence biomechanical performances of a tree in reorientation process: the production of juvenile wood in earlier stages of its life and the viscoelastic properties of wood tissues. Juvenile wood increases the flexibility of the stem for both softwoods and hardwoods. In the case of softwoods, viscoelasticity has only a minor influence on the stem flexibility. By contrast, it has an important positive impact on the flexibility of hardwoods and thus allows to speed up their reorientation process. The trade-off between stem flexibility and the efficiency of its reorientation may imply a biological limit on the magnitude of growth strain

A cosmogenic nuclide-derived chronology of pre-Last Glacial Cycle glaciations during MIS 8 and MIS 6 in northern Patagonia

International audienceThe precise environmental mechanisms controlling Quaternary glacial cycles remain ambiguous. To address this problem, it is critical to better comprehend the drivers of spatio-temporal variability in ice-sheet evolution by establishing reliable chronologies of former outlet-glacier advances. When spanning multiple glacial cycles, such chronologies have the capacity to contribute to knowledge on the topic of interhemispheric phasing of glaciations and climate events. In southern Argentina, reconstructions of this kind are achievable, as Quaternary expansions of the Patagonian Ice Sheet have emplaced a well-preserved geomorphological record covering several glacial cycles. Moreover, robust ice-sheet reconstructions from Patagonia are powerful barometers of former climate change, as Patagonian glaciers are influenced by the Southern Westerly Winds and the Antarctic Circumpolar Current coupled to them. It is essential to better constrain former shifts in these circulation mechanisms as they may have played a critical role in pacing regional and possibly global Quaternary climate change. Here, we present a new set of cosmogenic 10Be and 26Al exposure ages from pre-Last Glacial Cycle moraine boulder, glaciofluvial outwash cobble, and bedrock samples. This dataset constitutes the first direct chronology dating pre-Last Glacial Maximum (LGM) glacier advances in northern Patagonia and completes our effort to date the entire preserved moraine record of the Río Corcovado valley system (43° S, 71° W). We find that the outermost margins of the study site depict at least three distinct pre-Last Glacial Cycle stadials occurring around 290-270, 270-245, and 130-150 ka. Combined with the local LGM chronology, we discover that a minimum of four distinct Pleistocene stadials occurred during Marine Isotope Stages 8, 6, and 2 in northern Patagonia. Evidence for Marine Isotope Stage 4 and 3 deposits were not found at the study site. This may illustrate former longitudinal and latitudinal asynchronies in the Patagonian Ice Sheet mass balance during these Marine Isotope Stages. We find that the most extensive middle-to-late Pleistocene expansions of the Patagonian Ice Sheet appear to be out of phase with local summer insolation intensity but synchronous with orbitally controlled periods of longer and colder winters. Our findings thus enable the exploration of the potential roles of seasonality and seasonal duration in driving the southern mid-latitude ice-sheet mass balance, and they facilitate novel glacio-geomorphological interpretations for the study region. They also provide empirical constraints on former ice-sheet extent and dynamics that are essential for calibrating numerical ice-sheet and glacial isostatic adjustment models