{"id":348,"date":"2024-07-08T18:23:06","date_gmt":"2024-07-08T16:23:06","guid":{"rendered":"https:\/\/f4awz.wordpress.com\/?page_id=348"},"modified":"2024-07-08T18:23:06","modified_gmt":"2024-07-08T16:23:06","slug":"infos-version","status":"publish","type":"page","link":"https:\/\/maforge49.freeboxos.fr\/?page_id=348","title":{"rendered":"Infos version"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">OTPCrypto v1.02 du 08\/07\/2024<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">C&rsquo;est la derni\u00e8re version de OTPCrypto.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">La th\u00e9orie de Shannon montre l\u2019existence d\u2019un chiffre s\u00fbr : le chiffre de Vernam (one-time-pad). Sa s\u00e9curit\u00e9 repose sur le caract\u00e8re vraiment al\u00e9atoire d\u2019une clef aussi longue que le clair.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">En pratique cependant,<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>on ne sait pas g\u00e9n\u00e9rer de suite vraiment al\u00e9atoire<\/li>\n\n\n\n<li>une telle clef pose un probl\u00e8me de protocole : comment la transmettre de mani\u00e8re s\u00e9curis\u00e9e\u2026<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">En cryptographie sym\u00e9trique, on renonce \u00e0 la s\u00e9curit\u00e9 recommand\u00e9e par Shannon, au profit d\u2019une approche pragmatique : avoir la plus grande s\u00e9curit\u00e9 possible pour une clef de taille fix\u00e9e \u00e0 par exemple 128 ou 256 bits.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Pourquoi 128 bits ? <a href=\"https:\/\/webusers.imj-prg.fr\/~pascal.molin\/cours\/crypto\/tp_cryptanalyse.html#total-number-operations\">[tot11]<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">On suppose donc K=F2\u2113K=F2\u2113\u200b fix\u00e9, avec par exemple \u2113=128\u2113=128, et on suppose qu\u2019on sait choisir de mani\u00e8re al\u00e9atoire un \u00e9l\u00e9ment k\u2208Kk\u2208K.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Pour cela, deux grandes techniques :<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>le chiffrement par flot (stream cipher) : on construit une suite pseudo-al\u00e9atoire Lk:Z\u2192F2Lk\u200b:Z\u2192F2\u200b, et on utilise sa sortie pour pour faire un chiffre de Vernam (xor avec le clair).<\/li>\n\n\n\n<li>le chiffrement par bloc (block cipher) : on d\u00e9coupe le clair en blocs de \u2113\u2113 bits et on applique \u00e0 chacun un cryptosyst\u00e8me sur \u2113\u2113 bits.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Deux remarques pr\u00e9liminaires :<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Dans les deux cas, les m\u00e9thodes adopt\u00e9es combinent deux ingr\u00e9dients<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>un c\u00f4t\u00e9 alg\u00e9brique qui assure de la diffusion<\/li>\n\n\n\n<li>un c\u00f4t\u00e9 non-lin\u00e9aire qui assure la confusion.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Par ailleurs la tendance en cryptographie est de prendre pour chacun de ces ingr\u00e9dients un syst\u00e8me extr\u00e8mement simple, de sorte qu\u2019on suit les recommandations de Shannon sans y ajouter quoi que ce soit.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Attention avec le mot al\u00e9atoire :<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>pour faire un chiffrement par flot, on a besoin d\u2019une s\u00e9quence pseudo-al\u00e9atoire (qui ressemble \u00e0 de l\u2019al\u00e9a) mais parfaitement d\u00e9terministe, puisque devant ne d\u00e9couler que de la clef.<\/li>\n\n\n\n<li>pour choisir une clef (ou les param\u00e8tres d\u2019un cryptosyst\u00e8me), on a besoin d\u2019une source d\u2019al\u00e9a forte.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Les techniques actuelles pour obtenir de l\u2019al\u00e9a fort consistent la plupart du temps \u00e0 utiliser des chiffres par blocs nourris par des compteurs et des valeurs syst\u00e8me (heure, temp\u00e9rature du processeur). <\/p>\n","protected":false},"excerpt":{"rendered":"<p>OTPCrypto v1.02 du 08\/07\/2024 C&rsquo;est la derni\u00e8re version de OTPCrypto. La th\u00e9orie de Shannon montre l\u2019existence d\u2019un chiffre s\u00fbr : [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"class_list":["post-348","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.1 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Infos version - MaForge49<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/maforge49.freeboxos.fr\/?page_id=348\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Infos version - MaForge49\" \/>\n<meta property=\"og:description\" content=\"OTPCrypto v1.02 du 08\/07\/2024 C&rsquo;est la derni\u00e8re version de OTPCrypto. 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