Roger Odin, Les espaces de communication - Introduction à la sémio-pragmatique

Sommaire : Une hypothèse renouveléeDes priorités méthodologiquesVers une analyse poïétique de la communication ?Manifeste d’une communication pluriell

De Defoe à Tournier : le destin ou le désordre des choses. Sur trois incipit

Cet article étudie les rapports entre le désordre des choses et l'intervention du destin dans les incipit de Robinson Crusoe de Daniel Defoe, de Vendredi ou les Limbes du Pacifique de Michel Tournier (principalement), et de Vendredi ou la vie sauvage, du même auteur. Au début de Robinson Crusoe, le monde des hommes domine encore celui des choses, représentées plus tard sur l'île par des objets qui ont été conservés comme tels (sauvés du naufrage) ou confectionnés sur place, grâce aux outils eux aussi rescapés.L'incipit de Vendredi ou les Limbes du Pacifique organise au contraire le désordre des choses. Robinson, dont le destin récapitule la conception grecque (recoupant ainsi un certain nombre de mythes), celle du XVIIe siècle élisabéthain et une vision moderne peut-être issue de Voltaire, saura dépasser ce désordre, voire ensuite un ordre par lui reconstruit, pour se dissoudre dans l'immatériel. La valeur symbolique des objets qui, peuplant le navire, représentent l'ancien monde, s'atténue dans Vendredi ou la Vie sauvage, qui nous ramène à la force des choses.This article studies the relationship between the disorder of things and the interference of fate in the incipit of Defoe's Robinson Crusoe, Tournier's Vendredi ou les Limbes du Pacifique and, written by the same author, Vendredi ou la Vie sauvage. At the beginning of Robinson Crusoe, the world of men still dominates the world of things, later represented on the island by the objects preserved from the shipwreck or made there with tools that had been saved.On the contrary, the Vendredi ou les Limbes du Pacifique '5 incipit turns disorder into order. Robinson, whose destiny is influenced by the Greek conception of fate, the XVIIth Elizabethan worldview and by the modern vision that Voltaire maybe inspired, will take control of the disorder to impose a personal order and eventually dissolve into a totally ethereal being. The symbolic value of objects that were found on the ship and that represent the Old World is toned down in Vendredi ou la Vic sauvage, which brings us back to the reality and the power of material world

Another Look at the Cost of Cryptographic Attacks

This paper makes the case for considering the cost of cryptographic attacks as the main measure of their efficiency, instead of their time complexity. This allows, in our opinion, a more realistic assessment of the "risk" these attacks represent. This is half-and-half a position and a technical paper. Cryptographic attacks described in the literature are rarely implemented. Most exist only "on paper", and their main characteristic is that their estimated time complexity is small enough to break a given security property. However, when a cryptanalyst actually considers implementing an attack, she soon realizes that there is more to the story than time complexity. For instance, Wiener has shown that breaking the double-DES costs 2 6n/5 , asymptotically more than exhaustive search on n bits. We put forward the asymptotic cost of cryptographic attacks as a measure of their practicality. We discuss the shortcomings of the usual computational model and propose a simple abstract cryptographic machine on which it is easy to estimate the cost. We then study the asymptotic cost of several relevant algorithm: collision search, the three-list birthday problem (3XOR) and solving multivariate quadratic polynomial equations. We find that some smart algorithms cost much more than what their time complexity suggest, while naive and simple algorithms may cost less. Some algorithms can be tuned to reduce their cost (this increases their time complexity). Foreword A celebrated High Performance Computing paper entitled "Hitting the Memory Wall: Implications of the Obvious" [47] opens with these words: This brief note points out something obvious-something the authors "knew" without really understanding. With apologies to those who did understand, we offer it to those others who, like us, missed the point. We would like to do the same-but this note is not so short

Faster Algorithms for the Sparse Random 3XOR Problem

We present two new algorithms for a variant of the 3XOR problem with lists consisting of N n-bit 10 vectors whose coefficients are drawn randomly according to a Bernoulli distribution of parameter 11 p 0.13. The analysis of these algorithms reveal a "phase change" for a 16 certain threshold p. 17 2012 ACM Subject Classification Theory of computation → Computational complexity and cryp-18 tography; Theory of computation 1

Brute-Force Cryptanalysis with Aging Hardware: Controlling Half the Output of SHA-256

This paper describes a "three-way collision" on SHA-256 truncated to 128 bits. More precisely, it gives three random-looking bit strings whose hashes by SHA-256 maintain a non-trivial relation: their XOR starts with 128 zero bits. They have been found by brute-force, without exploiting any cryptographic weakness in the hash function itself. This shows that birthday-like computations on 128 bits are becoming increasingly feasible, even for academic teams without substantial means. These bit strings have been obtained by solving a large instance of the three-list generalized birthday problem, a difficult case known as the 3XOR problem. The whole computation consisted of two equally challenging phases: assembling the 3XOR instance and solving it. It was made possible by the combination of: 1) recent progress on algorithms for the 3XOR problem, 2) creative use of "dedicated" hardware accelerators, 3) adapted implementations of 3XOR algorithms that could run on massively parallel machines. Building the three lists required 2 67.6 evaluations of the compression function of SHA-256. They were performed in 7 calendar months by two obsolete secondhand bitcoin mining devices, which can now be acquired on eBay for about 80e. The actual instance of the 3XOR problem was solved in 300 CPU years on a 7-year old IBM Bluegene/Q computer, a few weeks before it was scrapped. To the best of our knowledge, this is the first explicit 128-bit collision-like result for SHA-256. It is the first bitcoin-accelerated cryptanalytic computation and it is also one of the largest public ones

Cryptanalysis of a Generalized Subset-Sum Pseudorandom Generator

We present attacks on a generalized subset-sum pseudorandom generator, which was proposed by von zur Gathen and Shparlinski in 2004. Our attacks rely on a sub-quadratic algorithm for solving a vectorial variant of the 3SUM problem, which is of independent interest. The attacks presented have complexities well below the brute-force attack, making the generators vulnerable. We provide a thorough analysis of the attacks and their complexities and demonstrate their practicality through implementations and experiments

D'eau et d'ombre, la caresse du virtuel

Cette recherche vise à déterminer en quoi la projection est un dispositif critique qui, confronté au vivant, peut permettre d’appréhender une rencontre entre le réel et le virtuel et tirer de celle-ci des impressions riches capables y compris de questionner le vivant. Mon travail met en jeu des projections sur des poissons bien vivants dans des installations. Je mets ainsi en scène des images « se faisant » dans des dispositifs qui mettent en lumière les caractéristiques essentielles de la projection et des ombres. Les ombres portées et les reflets sur l’eau qui sont les premières sources d’images auxquelles ait eu accès l’humanité. Les images produites dans ces conditions sont des images mobiles, instables, déformantes et « combinatoires », ce sont des images complexes, incomplètes, elles laissent un champ libre à l’imagination humaine qui a pu s’en emparer. Il est des dispositifs comme la salle de cinéma où le but est de faire adhérer sans réserve le spectateur à l’image virtuelle lumineuse. Mais il existe aussi d’autres dispositifs, artistiques, qui mettent en tension la projection et le réel. Dans ces cas, tout à fait fascinants selon moi, le spectateur perçoit l’image virtuelle comme fondue, matérialisée par le réel - corps, objet ou espace. Il peut donc percevoir une image incarnée, il peut enfin la saisir. En « s’incarnant », c’est-à-dire en heurtant un récepteur qui devient un écran et sur lequel l’image deviendra visible, l’image « prend » les qualités plastiques, de formes, de matières, de textures, de volumes de son récepteur. C’est ainsi qu’il se crée un double échange, une « rencontre » entre l’image qui modifie notre perception de son récepteur physique, le couvre de son motif et le récepteur qui donne sa peau et sa matérialité à l’image