Modélisation oscillatoire de l'écriture manuscrite

Dans ce travail de thèse, nous proposons un modèle oscillatoire de la production de traces écrites, appelé POMH, où l'écriture est vue comme la composition du mouvement de deux oscillateurs orthogonaux du plan. Il s'agit d'une extension du modèle classique d'Hollerbach, qui a été simplifié et rendu symétrique, permettant ainsi une méthode très rapide d'extraction de ses paramètres à partir de traces réelles enregistrées. Nous comparons cet algorithme avec une méthode d'optimisation usuelle afin de montrer son efficacité. Nous montrons que POMH permet de rivaliser avec un modèle répandu de la génération de trace, en terme de précision de reproduction de formes simples. Il est ensuite confronté, avec succès, à des traces plus complexes telles que des phrases entières ou des caractères chinois. Dans un second temps, nous cherchons à interroger les liens entre ces deux oscillateurs. Pour cela nous étudions leur phase relative, nous appuyant sur une approche dynamique de la coordination motrice. Nous tentons d'apporter des éléments de réponses à deux questions : (i) Y-a-t-il, comme pour le tracé d'ellipses, des coordinations préférentielles lorsque l'on écrit ? (ii) Quels sont les liens entre vitesse d'écriture et géométrie de la trace écrite ? Pour tenter de répondre à la première question, deux expérimentations sont faites. La première cherche à valider le calcul de la phase relative continue sur de l'écriture réelle. La seconde étudie l'existence éventuelle de patrons de coordinations (représentés par la phase relative) préférentiels pour la tâche d'écriture chez l'adulte. Pour tenter de répondre à la deuxième question, nous formulons deux hypothèses concernant l'évolution du paysage des patrons de coordination préférentiels avec la vitesse d'écriture. Nous proposons alors deux protocoles expérimentaux (non réalisés) qui permettraient de les valider. Dans un dernier temps, nous inscrivant dans un cadre interactiviste, nous proposons un modèle simplifié de reconnaissance de caractères, basé sur l'idée que lecture et écriture partagent un grand nombre de leurs mécanismes. Nous commençons par une recherche dans la littérature des preuves de ces liens entre perception et action pour toutes les modalités, et en particulier pour l'écriture cursive. Nous proposons ensuite deux algorithmes implémentant la perception de l'écriture comme une simulation intériorisée. Le premier utilise POMH comme représentation interne des caractères ; le second est basé sur le concept d'"images temporalisées" et donne de meilleurs résultats.In this thesis, we propose an oscillatory model of handwritten production, called POMH, where handwriting is considered as the combination of movement of two oscillators. It derives from the classical Hollerbach model which has been simplified and symmetrized, allowing for a fast method of extraction of its parameters from recorded strokes. We compare this algorithm with a Newton-based optimization method in order to prove its efficiency. We show that POMH is as good as the widespread Edelman-Flash model, in terms of accuracy at reproducing simple shapes. Then, it is successfully applied to more complicated handwritten strokes such as entire sentences or Chinese characters. In a second time, we aim at explaining the correlations between these two oscillators. In that purpose, we study their relative phase, based on the dynamical approach of motor coordination. We try to answer these two questions : (i) Is there, like it is the case in the drawing of ellipses, preferred coordinations in the handwriting movement ? (ii) What are the links between handwriting speed and the geometry of the produced trace ? In order to answer the first question, two experiments have been conducted. The first aims at validating the continuous relative phase computation on real handwriting; the second studies the possible existence of preferred coordination patterns in the handwriting task. To begin to answer the second question, we propose two hypotheses and two experiments that would allow to validate them. In a last effort, based on the interactivist theory, we propose a simplified model of off-line handwriting recognition, using the idea that reading and handwriting share a lot of their mechanisms. We first begin by a search, in the literature, for evidence of the links between perception and action for all modalities, particularly regarding handwriting. We then propose two algorithms implementing handwriting perception as an inner simulation. The first uses POMH as an internal representation of characters; the second is based on the concept of "temporalized images" and gives better results

Effects of α-synuclein levels on cerebral synaptic function: Validation of a novel PET radioligand for the early diagnosis of Parkinson’s disease

Background In Parkinson’s disease, converging evidence supports a pathogenic role for excessive α–synuclein accumulation in synaptic terminals that may propagate back to the soma of vulnerable nerve cells such as neurons in the substantia nigra pars compacta. The resulting loss of dopaminergic terminals in the striatum can be demonstrated in vivo using 18F-Dopa-PET (positron emission tomography). However, there’s currently no validated biomarker of the progressive synaptic dysfunction in other vulnerable areas such as the cerebral cortex. Goal In this longitudinal study, we will test the hypothesis that the loss of synaptic terminals in a mouse model of excessive α–synuclein accumulation can be demonstrated in vivo before the occurrence of behavioural disturbances using 18F-UCB-H, a new PET biomarker developed at CRC. We will also test if this new imaging modality is sensitive enough to study the effect of a disease modifying therapy such as chronic physical exercise. Methods We will use microPET for the in vivo quantification of 18F-UCB-H brain uptake in 16 wild type animals and 16 transgenic (Tg) mice overexpressing human α–syn under the mThy1 promotor every 2 months. Data will be validated against post-mortem analyses after the last PET study. Predictions We predict decreased tracer uptake over time in the basal ganglia and cerebral cortex in Tg mice as compared with WT animals. Also, we predict a relationship between 18F-UCB-H uptake levels in basal ganglia and cerebral cortex and progressive alterations in both motor and cognitive functions, respectively. Further, we also expect that chronic exercise will slow down both motor and cognitive disturbances, as well as the rate of 18F-UCB-H brain uptake decreases. Conclusion If 18F-UCB-H PET proves to be a valid biomarker for the early detection of α–synuclein accumulation in the pre-clinical model of PD, the methods will tested on human clinical populations

Mapping track density changes in nigrostriatal and extranigral pathways in Parkinson's disease

peer reviewedHighlights First whole-brain probabilistic tractography study in Parkinson's disease High quality diffusion-weighted images (120 gradient directions, b = 2500 s/mm2) Voxel-based group analysis comparing early-stage patients and controls Abnormal reconstructed track density in the nigrostriatal pathway and brainstem Track density also increased in limbic and cognitive circuits

Clustering effect in Simon and Simeck

SIMON and SIMECK are two lightweight block ciphers with a simple round function using only word rotations and a bit-wise AND operation. Previous work has shown a strong clustering effect for differential and linear cryptanalysis, due to the existence of many trails with the same inputs and outputs. In this paper, we explore this clustering effect by exhibiting a class of high probability differential and linear trails where the active bits stay in a fixed window of w bits. Instead of enumerating a set of good trails contributing to a differential or a linear approximation, we compute the probability distribution over this space, including all trails in the class. This results in stronger distinguishers than previously proposed, and we describe key recovery attacks against SIMON and SIMECK improving the previous results by u

QCB: Efficient Quantum-Secure Authenticated Encryption

International audienceIt was long thought that symmetric cryptography was only mildly affected by quantum attacks, and that doubling the key length was sufficient to restore security. However, recent works have shown that Simon's quantum period finding algorithm breaks a large number of MAC and authenticated encryption algorithms when the adversary can query the MAC/encryption oracle with a quantum superposition of messages. In particular, the OCB authenticated encryption mode is broken in this setting, and no quantum-secure mode is known with the same efficiency (rate-one and parallelizable). In this paper we generalize the previous attacks, show that a large class of OCB-like schemes is unsafe against superposition queries, and discuss the quantum security notions for authenticated encryption modes. We propose a new rate-one parallelizable mode named QCB inspired by TAE and OCB and prove its security against quantum superposition queries

Quantum linearization attacks

Recent works have shown that quantum period-finding can be used to break many popular constructions (some block ciphers such as Even-Mansour, multiple MACs and AEs...) in the superposition query model. So far, all the constructions broken exhibited a strong algebraic structure, which enables to craft a periodic function of a single input block. Recoverin

Internal Symmetries and Linear Properties: Full-permutation Distinguishers and Improved Collisions on Gimli

International audienceGimli is a family of cryptographic primitives (both a hash function and an AEAD scheme) that has been selected for the second round of the NIST competition for standardizing new lightweight designs. The candidate Gimli is based on the permutation Gimli, which was presented at CHES 2017. In this paper, we study the security of both the permutation and the constructions that are based on it. We exploit the slow diffusion in Gimli and its internal symmetries to build, for the first time, a distinguisher on the full permutation of complexity 2 64. We also provide a practical distinguisher on 23 out of the full 24 rounds of Gimli that has been implemented. Next, we give (full state) collision and semi-free-start collision attacks on Gimli-Hash, reaching respectively up to 12 and 18 rounds. On the practical side, we compute a collision on 8-round Gimli-Hash. In the quantum setting, these attacks reach 2 more rounds. Finally, we perform the first study of linear trails in Gimli, and we find a linear distinguisher on the full permutation

Saturnin: a suite of lightweight symmetric algorithms for post-quantum security

International audienceThe cryptographic algorithms needed to ensure the security of our communications have a cost. For devices with little computing power, whose number is expected to grow significantly with the spread of the Internet of Things (IoT), this cost can be a problem. A simple answer to this problem is a compromise on the security level: through a weaker round function or a smaller number of rounds, the security level can be decreased in order to cheapen the implementation of the cipher. At the same time, quantum computers are expected to disrupt the state of the art in cryptography in the near future. For public-key cryptography, the NIST has organized a dedicated process to standardize new algorithms. The impact of quantum computing is harder to assess in the symmetric case but its study is an active research area.In this paper, we specify a new block cipher, Saturnin, and its usage in different modes to provide hashing and authenticated encryption in such a way that we can rigorously argue its security in the post-quantum setting. Its security analysis follows naturally from that of the AES, while our use of components that are easily implemented in a bitsliced fashion ensures a low cost for our primitives. Our aim is to provide a new lightweight suite of algorithms that performs well on small devices, in particular micro-controllers, while providing a high security level even in the presence of quantum computers. Saturnin is a 256-bit block cipher with a 256-bit key and an additional 9-bit parameter for domain separation. Using it, we built two authenticated ciphers and a hash function.• Saturnin-CTR-Cascade is an authenticated cipher using the counter mode and a separate MAC. It requires two passes over the data but its implementation does not require the inverse block cipher.• Saturnin-Short is an authenticated cipher intended for messages with a length strictly smaller than 128 bits which uses only one call to Saturnin to providenconfidentiality and integrity.• Saturnin-Hash is a 256-bit hash function.In this paper, we specify this suite of algorithms and argue about their security in both the classical and the post-quantum setting