{"id":53444,"date":"2019-12-02T00:00:00","date_gmt":"2019-12-01T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/shema-razdeleniya-sekreta-shamira"},"modified":"2020-02-18T14:01:21","modified_gmt":"2020-02-18T11:01:21","slug":"shema-razdeleniya-sekreta-shamira","status":"publish","type":"post","link":"https:\/\/prohoster.info\/da\/blog\/administrirovanie\/shema-razdeleniya-sekreta-shamira","title":{"rendered":"Shamir's Secret Sharing Scheme","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Lad os overveje et scenarie, hvor det er n\u00f8dvendigt at sikre et bankskabet. Det betragtes som fuldst\u00e6ndig utilg\u00e6ngeligt uden n\u00f8glen, som du f\u00e5r udleveret den f\u00f8rste arbejdsdag. Dit m\u00e5l er at opbevare n\u00f8glen sikkert.<\/p>\n<p>Antag, at du beslutter at opbevare n\u00f8glen hos dig selv hele tiden og kun give adgang til skabet efter behov. Men du vil hurtigt indse, at en s\u00e5dan l\u00f8sning ikke skalerer godt i praksis, fordi dit fysiske n\u00e6rv\u00e6r altid er n\u00f8dvendigt for at \u00e5bne skabet. Hvad med den ferie, de lovede dig? Desuden er der et endnu mere skr\u00e6mmende sp\u00f8rgsm\u00e5l: hvad nu hvis du mister den eneste n\u00f8gle?<\/p>\n<p>Med tanken om ferien besluttede du at lave en kopi af n\u00f8glen og betro den til en anden medarbejder. Men du forst\u00e5r, at det heller ikke er ideelt. Ved at fordoble antallet af n\u00f8gler har du ogs\u00e5 fordoblet mulighederne for, at n\u00f8glen kan blive stj\u00e5let.<\/p>\n<p>Fortvivlet \u00f8del\u00e6gger du kopien og beslutter at dele den originale n\u00f8gle i to. Nu t\u00e6nker du, at to betroede personer med fragmenter af n\u00f8glen skal v\u00e6re til stede fysisk for at samle n\u00f8glen og \u00e5bne skabet. Det betyder, at tyven skal stj\u00e6le to fragmenter, hvilket g\u00f8r det sv\u00e6rere end at stj\u00e6le en enkelt n\u00f8gle. Men snart indser du, at denne ordning ikke er meget bedre end blot \u00e9n n\u00f8gle, fordi hvis nogen mister halvdelen af n\u00f8glen, kan den fulde n\u00f8gle ikke genoprettes.<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><br \/>\nProblemet kan l\u00f8ses med en r\u00e6kke ekstra n\u00f8gler og l\u00e5se, men med denne tilgang vil der hurtigt v\u00e6re brug for <i>mange<\/i> n\u00f8gler og l\u00e5se. Du beslutter, at i en ideel ordning skal n\u00f8glen deles, s\u00e5 sikkerheden ikke helt afh\u00e6nger af \u00e9n person. Du konkluderer ogs\u00e5, at der skal v\u00e6re en t\u00e6rskel for antallet af fragmenter, s\u00e5 ved tab af et fragment (eller hvis en person tager p\u00e5 ferie), forbliver den samlede n\u00f8gle funktionel.<\/p>\n<h1>Hvordan man deler et hemmelighed<\/h1>\n<p>\nOm denne type n\u00f8gleh\u00e5ndteringsordning t\u00e6nkte Adi Shamir i 1979, da han publicerede sit arbejde <noindex><a rel=\"nofollow\" href=\"https:\/\/cs.jhu.edu\/~sdoshi\/crypto\/papers\/shamirturing.pdf\">\u00bbHvordan man deler et hemmelighed\u00ab<\/a><\/noindex>. Artiklen forklarer kort den s\u00e5kaldte <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/64d1d06429d10e2571b04ba756a9e44d.jpg\" style=\"display:block;margin: 0 auto;\" \/> t\u00e6rskelsordning for effektivt at dele en hemmelig v\u00e6rdi (f.eks. en kryptografisk n\u00f8gle) op i <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/d2ecc715b363a149fefb4cc647a30e6e.jpg\" style=\"display:block;margin: 0 auto;\" \/> dele. Derefter, n\u00e5r og kun n\u00e5r mindst <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/7a3f94d0d7874387726d18ef0c5c4174.jpg\" style=\"display:block;margin: 0 auto;\" \/> af <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/83808316ecdccf2d3d1d05696c6d5507.jpg\" style=\"display:block;margin: 0 auto;\" \/> dele er samlet, kan hemmeligheden let genoprettes. <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/ec92794c36ed48497df201c55697e065.jpg\" style=\"display:block;margin: 0 auto;\" \/>.<\/p>\n<p>Set fra et sikkerhedsm\u00e6ssigt synspunkt er en vigtig egenskab ved denne skema, at en angriber ikke skal vide noget som helst, hvis han ikke har mindst <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/49419db7a603359c9d7f2949263e0f7d.jpg\" style=\"display:block;margin: 0 auto;\" \/> dele. Selv tilstedev\u00e6relsen af <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/13aad9d68bc8f0729bf06fc49435b7dc.jpg\" style=\"display:block;margin: 0 auto;\" \/> dele m\u00e5 ikke give nogen information. Vi kalder denne egenskab <i>semantisk sikkerhed<\/i>.<\/p>\n<h1>Polynomiel interpolation<\/h1>\n<p>\nShamir's t\u00e6rskelskema <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/5bcbb5a7f61e4e37103c379964d49e63.jpg\" style=\"display:block;margin: 0 auto;\" \/> er bygget op omkring begrebet <b>polynomiel interpolation<\/b>. Hvis du ikke er bekendt med dette begreb, er det faktisk ret enkelt. Generelt, hvis du nogensinde har tegnet punkter p\u00e5 en graf og derefter forbundet dem med linjer eller kurver, s\u00e5 har du allerede brugt det!<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/66d66cc226dde7af9d71ab1ad7f92eea.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<i>Gennem to punkter kan der tr\u00e6kkes et ubegribelig antal polynomer af grad 2. For at v\u00e6lge et unikt polynom kr\u00e6ves et tredje punkt. Illustration: <noindex><a rel=\"nofollow\" href=\"https:\/\/ru.wikipedia.org\/wiki\/%D0%A1%D1%85%D0%B5%D0%BC%D0%B0_%D1%80%D0%B0%D0%B7%D0%B4%D0%B5%D0%BB%D0%B5%D0%BD%D0%B8%D1%8F_%D1%81%D0%B5%D0%BA%D1%80%D0%B5%D1%82%D0%B0_%D0%A8%D0%B0%D0%BC%D0%B8%D1%80%D0%B0#\/media\/File:3_polynomials_of_degree_2_through_2_points.svg\">Wikipedia<\/a><\/noindex><\/i> <\/p>\n<p>Lad os overveje et polynom af grad \u00e9n, <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/479ff09339b6907cf7fd5420a6b66907.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Hvis du vil opbygge denne funktion p\u00e5 grafen, hvor mange punkter har du brug for? N\u00e5, vi ved, at det er en line\u00e6r funktion, der danner en linje, og derfor kr\u00e6ver det mindst to punkter. Lad os dern\u00e6st overveje en polynomiel funktion af grad to, <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/bd6591a5e317fadba394b9f93c03f813.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Dette er en kvadratisk funktion, s\u00e5 til opbygning af grafen kr\u00e6ves mindst tre punkter. Hvad med et polynom af grad tre? Mindst fire punkter. Og s\u00e5 videre og s\u00e5 videre.<\/p>\n<p>Det virkelig fede ved denne egenskab er, at givet graden af den polynomielle funktion og mindst <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/97d23bb431f561738675a8eecd78c8bd.jpg\" style=\"display:block;margin: 0 auto;\" \/> punkter, kan vi udlede yderligere punkter for denne polynomielle funktion. Ekstrapoleringen af disse yderligere punkter kalder vi <i>polynomiel interpolation<\/i>.<\/p>\n<h1>Sammens\u00e6tning af hemmeligheden<\/h1>\n<p>\nM\u00e5ske har du allerede indset, at den smarte Shamir's skema tr\u00e6der i kraft her. Lad os antage, at vores hemmelighed <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/9f18d04feb91617cc6b17ee999f7621e.jpg\" style=\"display:block;margin: 0 auto;\" \/> \u2014 det er <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/724e6fe3c0b6e8460207592d515dde4a.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Vi kan omdanne <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/e1bb80717e0e060d77dc3fa2bff5e396.jpg\" style=\"display:block;margin: 0 auto;\" \/> til et punkt p\u00e5 grafen <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/d7291bf682131a3cd1dc9fb65c351a5d.jpg\" style=\"display:block;margin: 0 auto;\" \/> og finde p\u00e5 en polynomiel funktion af grad <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c63b9a9efa9409f73baf5916cd77b8b5.jpg\" style=\"display:block;margin: 0 auto;\" \/>, som opfylder dette punkt. Lad os huske, at <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/4670e092c7dc86f70984a3d5e875ae7e.jpg\" style=\"display:block;margin: 0 auto;\" \/> vil v\u00e6re vores t\u00e6rskel for de n\u00f8dvendige fragmenter, s\u00e5 hvis vi s\u00e6tter t\u00e6rsklen til tre fragmenter, skal vi v\u00e6lge en polynomiel funktion af grad to.<\/p>\n<p>Vores polynom vil have formen <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/06e96a58093b9e00d7c37ad5f832a6f4.jpg\" style=\"display:block;margin: 0 auto;\" \/>, hvor <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/fc9ce1b274e8224fcfee33290fee6455.jpg\" style=\"display:block;margin: 0 auto;\" \/> og <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/ec120b09589c1ee882f1f93b47626c94.jpg\" style=\"display:block;margin: 0 auto;\" \/> \u2014 tilf\u00e6ldigt valgte positive heltal. Vi bygger kun et polynom af grad <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/ef10f07dfb8496cca70579246c1d9c48.jpg\" style=\"display:block;margin: 0 auto;\" \/>, hvor konstantleddet <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/d7db113a15325721c9fea613a379026f.jpg\" style=\"display:block;margin: 0 auto;\" \/>\u00a0er vores hemmelighed <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/093bd4575a590bed819e6ec9f9b41aa0.jpg\" style=\"display:block;margin: 0 auto;\" \/>, og hver af de efterf\u00f8lgende <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/6c33d819871b32ff7d347d00408d02d1.jpg\" style=\"display:block;margin: 0 auto;\" \/> medlemmer er tilf\u00e6ldigt valgt med en positiv koefficient. Hvis vi vender tilbage til det oprindelige eksempel og antager, at <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c6ff5a7ad5a6a82ae31c583148ea5274.jpg\" style=\"display:block;margin: 0 auto;\" \/>, s\u00e5 vil vi f\u00e5 en funktion <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/b3386ca5ec27e0dacd17874d6f5720c8.jpg\" style=\"display:block;margin: 0 auto;\" \/>.<\/p>\n<p>P\u00e5 dette stadium kan vi generere fragmenter ved at tilslutte <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/50a46de4540f90ddba6b1bbfa3702892.jpg\" style=\"display:block;margin: 0 auto;\" \/> unikke hele tal i <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/fcbc7f0b6d9353e6eae0fafe4a06a4f2.jpg\" style=\"display:block;margin: 0 auto;\" \/>, hvor <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c58e20b2b97950112194f6a51707289c.jpg\" style=\"display:block;margin: 0 auto;\" \/> (for det er vores hemmelighed). I dette eksempel \u00f8nsker vi at tildele fire fragmenter med en t\u00e6rskel p\u00e5 tre, s\u00e5 vi genererer tilf\u00e6ldigt punkter <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/720b820e264f0314cb2e14ab6502ee96.jpg\" style=\"display:block;margin: 0 auto;\" \/> og sender et punkt til hver af de fire betroede personer, n\u00f8glebevarerne. Vi informerer ogs\u00e5 folk om, at <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c441ff2a652b58011e13d60855c7e404.jpg\" style=\"display:block;margin: 0 auto;\" \/>, da dette betragtes som offentlig information og er n\u00f8dvendigt for gendannelse <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/2011019c98b6d1a77a0cd25a3667c9e4.jpg\" style=\"display:block;margin: 0 auto;\" \/>.<\/p>\n<h1>Gendannelse af hemmeligheden<\/h1>\n<p>\nVi har allerede diskuteret konceptet om polynomiel interpolation og at det ligger til grund for Shamirs t\u00e6rskelschema <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/6f93e17d2d2ce5659972b98a9c8eee83.jpg\" style=\"display:block;margin: 0 auto;\" \/>. N\u00e5r som helst tre af de fire betroede personer \u00f8nsker at gendanne <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/9b5ba8c78e395d3dee229e222c31d85a.jpg\" style=\"display:block;margin: 0 auto;\" \/>, skal de blot interpolere <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/cfec467c0571c4d54d74938c5667146f.jpg\" style=\"display:block;margin: 0 auto;\" \/> med deres unikke punkter. For dette kan de definere deres punkter <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/035e1f8407434fdbe1b8814d7fd3ee1f.jpg\" style=\"display:block;margin: 0 auto;\" \/> og beregne Lagranges interpolationspolynomium ved at bruge f\u00f8lgende formel. Hvis programmering er mere forst\u00e5eligt for dig end matematik, s\u00e5 er pi i bund og grund en operator <code>til<\/code>, der multiplicerer alle resultaterne, mens sigma er <code>til<\/code>, der l\u00e6gger alt sammen.<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/01a47d3bc38f07f7b65da2ca1f772e28.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p><\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/cc0039bc38e27a62161bc0fde3b1472d.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\nVed <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/b41d5abefcac0bb813291063f0a56404.jpg\" style=\"display:block;margin: 0 auto;\" \/> kan vi l\u00f8se dette som f\u00f8lger og returnere vores oprindelige polynomiefunktion:<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/b7af6d68d1fa639442f96ed11cc96bd7.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\nDa vi ved, at <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/df250c5c331d0a2903867efcad71d325.jpg\" style=\"display:block;margin: 0 auto;\" \/>, gendannelsen <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/a6968a889776d0caa3db0dd6e10842d4.jpg\" style=\"display:block;margin: 0 auto;\" \/> udf\u00f8res ganske enkelt:<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/b89862098c973d18a75a104092364a04.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p><\/p>\n<h1>Brug af usikker heltalsarithmetic<\/h1>\n<p>\nSelvom vi har anvendt den grundl\u00e6ggende id\u00e9 fra Shamir med succes <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/626be5c238019fc0a2ff08798b8e620c.jpg\" style=\"display:block;margin: 0 auto;\" \/>, st\u00e5r vi over for et problem, som vi har ignoreret indtil nu. Vores polynomielle funktion bruger usikker heltalsarithmetic. Husk, at for hver ekstra punkt, en angriber f\u00e5r p\u00e5 grafen af vores funktion, er der f\u00e6rre muligheder for andre punkter tilbage. Du kan se det med egne \u00f8jne, n\u00e5r du bygger grafen med et stigende antal punkter for en polynomiel funktion ved brug af heltalsarithmetic. Dette er kontraproduktivt for vores erkl\u00e6rede sikkerhedsm\u00e5l, fordi en angriber ikke b\u00f8r l\u00e6re noget som helst, f\u00f8r de har mindst <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/d5278c748b7713fc387c37425d43656d.jpg\" style=\"display:block;margin: 0 auto;\" \/> fragmenter.<\/p>\n<p>For at demonstrere, hvor svagt skemaet med heltalsarithmetic er, lad os overveje et scenarie, hvor angriberen har f\u00e5et to punkter <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/ebe75137fa19aaccdc733618707de3c0.jpg\" style=\"display:block;margin: 0 auto;\" \/> og kender den offentlige information, at <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/45dc1dbd7564637c96d1c8383af19e15.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Fra disse oplysninger kan han udlede <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/16e75561bf051ecd3232f0560f75e494.jpg\" style=\"display:block;margin: 0 auto;\" \/>, der svarer til to, og inds\u00e6tte de kendte v\u00e6rdier i formlen <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/e6c550b9a0d630e62d5be66e61ff3a89.jpg\" style=\"display:block;margin: 0 auto;\" \/> og <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/e2a3c2a324c159cf73852513dda5ff3b.jpg\" style=\"display:block;margin: 0 auto;\" \/>.<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/003b535b08b5de17b573c7af61110dbb.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\n Derefter kan angriberen finde <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/76d496e3442e88c7d5a238612f2ee8da.jpg\" style=\"display:block;margin: 0 auto;\" \/>, ved at beregne <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/96ef9b4a0657cd258978e2eda974bd09.jpg\" style=\"display:block;margin: 0 auto;\" \/>:<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/8e677012c61e1cc45f1f3be6e44aa1c1.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\nDa vi har defineret <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/62af08665bef7cd3fc447411455352c6.jpg\" style=\"display:block;margin: 0 auto;\" \/> som tilf\u00e6ldigt valgte hele positive tal, er der et begr\u00e6nset antal mulige <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/66c39a1014c0acab55fea137f28a6d0f.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Ved hj\u00e6lp af disse oplysninger kan angriberen udlede <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/0c3caaa1e189ffea0001ca9ad08a65d1.jpg\" style=\"display:block;margin: 0 auto;\" \/>, da alt over 5 vil g\u00f8re <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/104807891ce9ab1d3adc649f8d1dcd29.jpg\" style=\"display:block;margin: 0 auto;\" \/> negativt. Dette viser sig at v\u00e6re sandt, da vi har defineret <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/cf2bebff28344be58b02c492fd0e49ba.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>Derefter kan angriberen beregne mulige v\u00e6rdier <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/7c9c09333ee4ab432122e959892daeda.jpg\" style=\"display:block;margin: 0 auto;\" \/>, ved at erstatte <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c5d88d7a2488ae0c40e5ec3edb66dd2d.jpg\" style=\"display:block;margin: 0 auto;\" \/> i <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/8fd97c507a4d2bc8d4e4619e10e97063.jpg\" style=\"display:block;margin: 0 auto;\" \/>:<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/1f2fb897dc37702dd543a6d7783339cb.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\nMed et begr\u00e6nset s\u00e6t muligheder for <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/9960ad727ecf47084cacfb9f487f329a.jpg\" style=\"display:block;margin: 0 auto;\" \/> bliver det klart, hvor let det er at g\u00e6tte og verificere v\u00e6rdierne <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/47f9786e9728ed72e10dd505d7445b41.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Her er der kun fem muligheder.<\/p>\n<h1>L\u00f8sningen p\u00e5 problemet med usikker heltalsaritmetik<\/h1>\n<p>\nFor at afhj\u00e6lpe denne s\u00e5rbarhed foresl\u00e5r Shamir at anvende modul\u00e6r aritmetik og erstatte <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/503fd220af76c5e96cce3a84a4673f91.jpg\" style=\"display:block;margin: 0 auto;\" \/> og f\u00e5 en fungerende kommando. <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/49ab2b2ee61d6551a1b41f6a1795a295.jpg\" style=\"display:block;margin: 0 auto;\" \/>, hvor <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/bb5a5adda52f7d4dd401efd8a040be69.jpg\" style=\"display:block;margin: 0 auto;\" \/> og <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/1e062a8784dfb6da2bc708d3de027042.jpg\" style=\"display:block;margin: 0 auto;\" \/> \u2014 m\u00e6ngden af alle primtal.<\/p>\n<p>Lad os hurtigt mindes om, hvordan modul\u00e6r aritmetik fungerer. V\u00e6kkere med visere er et velkendt koncept. Det bruger ur, som er <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/93520a0c8bdbbe57ab424e58c3bbfe30.jpg\" style=\"display:block;margin: 0 auto;\" \/>. S\u00e5 snart timeviseren g\u00e5r forbi tolv, vender den tilbage til \u00e9n. En interessant egenskab ved dette system er, at bare ved at se p\u00e5 klokken kan vi ikke udlede, hvor mange omdrejninger timeviseren har gjort. Men hvis vi ved, at timeviseren har passeret 12 fire gange, kan vi fuldst\u00e6ndig bestemme antallet af forl\u00f8bne timer ved hj\u00e6lp af en simpel formel <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/5b8b7655f38ee900b989fdc070616a6b.jpg\" style=\"display:block;margin: 0 auto;\" \/>, hvor <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/0ec5da4245e1eac619b42bb62f682773.jpg\" style=\"display:block;margin: 0 auto;\" \/>\u00a0\u2014 det er vores divisor (her <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/a8656dac61ddb1097f06781c5b5aad69.jpg\" style=\"display:block;margin: 0 auto;\" \/>), <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/3ba5b3dc4f29fac3c9d4f5f2072d688b.jpg\" style=\"display:block;margin: 0 auto;\" \/>\u00a0\u2014 er kvotienten (hvor mange gange divisoren uden rest g\u00e5r ind i det oprindelige tal, her <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/ac9bb70e1511109b0181e14b6227f57e.jpg\" style=\"display:block;margin: 0 auto;\" \/>), mens <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/57b6842c2bfd39b19ce428e5b9345946.jpg\" style=\"display:block;margin: 0 auto;\" \/>\u00a0\u2014 er resten, som normalt returneres af modulus operatoren (her <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/28f71e672ecc717d2bd1845e27273398.jpg\" style=\"display:block;margin: 0 auto;\" \/>). At kende alle disse v\u00e6rdier g\u00f8r det muligt for os at l\u00f8se ligningen for <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/9548f9d6b522258582be1f8968752866.jpg\" style=\"display:block;margin: 0 auto;\" \/>, men hvis vi springer kvotienten over, vil vi aldrig kunne genskabe den oprindelige v\u00e6rdi.<\/p>\n<p>Vi kan demonstrere, hvordan dette forbedrer sikkerheden i vores skema ved at anvende skemaet til vores tidligere eksempel og bruge <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c0f760bdd2b67444bd233d4ea7fe5e72.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Vores nye polynomiske funktion <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/afddb9747f68076bc6dbe9b5cf60d107.jpg\" style=\"display:block;margin: 0 auto;\" \/>, og de nye punkter <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/da9d9ecfcf949b6be4bc8e3a29d670ab.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Nu kan n\u00f8glebevarerne igen bruge polynomiel interpolation til at genskabe vores funktion, men denne gang skal operationerne addition og multiplikation ledsages af reduktion modulo <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/f94ae5343347b38dc64228472b564f0e.jpg\" style=\"display:block;margin: 0 auto;\" \/> (f.eks. <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/d19138189cd40c6c01ab68d3d6b7027b.jpg\" style=\"display:block;margin: 0 auto;\" \/>).<\/p>\n<p>Ved hj\u00e6lp af dette nye eksempel, antag at angriberen kender to af disse nye punkter, <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/4f13c2640360f124305f3f023d6cfa83.jpg\" style=\"display:block;margin: 0 auto;\" \/>, og de offentlige oplysninger <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/376e0e059b761e3f3e7473d8d2d3428f.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Denne gang udleder angriberen baseret p\u00e5 al den information, han har, f\u00f8lgende funktioner, hvor <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/f0aedf279cc2418e2d62d51e63e324b2.jpg\" style=\"display:block;margin: 0 auto;\" \/>\u00a0\u2014 m\u00e6ngden af alle positive hele tal, og <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c92efad35129d61013f6e37ec1907fd3.jpg\" style=\"display:block;margin: 0 auto;\" \/> repr\u00e6senterer modulkoefficienten. <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c2679ec08a40d7aa13a9d375b610642c.jpg\" style=\"display:block;margin: 0 auto;\" \/>.<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/0f6d09b6c15f013e9a445fef060f8091.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\nNu finder vores angriber igen <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/8e01640ea802740996150d09277cbf1f.jpg\" style=\"display:block;margin: 0 auto;\" \/>, ved at beregne <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/78fa395ca715c36835c38f4fe16d63e0.jpg\" style=\"display:block;margin: 0 auto;\" \/>:<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/d739d7e52d675aeba9abcc6ada4097e1.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\nDerefter pr\u00f8ver han igen at udlede <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/e47c9bd27ac92787c287b7db249a345f.jpg\" style=\"display:block;margin: 0 auto;\" \/>, ved at erstatte <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/15c82f6824ad986351d3358c32b28f26.jpg\" style=\"display:block;margin: 0 auto;\" \/> i <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/56cddebdf83ddc105aa8aba91bd0bb38.jpg\" style=\"display:block;margin: 0 auto;\" \/>:<\/p>\n<p><img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/6e9643108864d1d2cf9e04bed493fff7.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/p>\n<p>\nDenne gang har han et alvorligt problem. V\u00e6rdier mangler i formlen <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/217282ca338c79dd058db66f405b07a0.jpg\" style=\"display:block;margin: 0 auto;\" \/>, <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/fb908d84b7eac873bba662cf69d95b95.jpg\" style=\"display:block;margin: 0 auto;\" \/> og <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/83389928ca52ffce5266fe6a414e1f18.jpg\" style=\"display:block;margin: 0 auto;\" \/>. Da der er et uendeligt antal kombinationer af disse variabler, kan han ikke f\u00e5 nogen yderligere information.<\/p>\n<h1>Sikkerhedsovervejelser<\/h1>\n<p>\nShamir's hemmelighedsdeleskema tilbyder <i>sikkerhed set fra informationsteoriens synspunkt.<\/i>. Det betyder, at matematikken er robust selv mod en angriber med ubegr\u00e6nsede beregningsressourcer. Dog indeholder skemaet stadig flere kendte problemer.<\/p>\n<p>For eksempel skaber Shamir's skema ikke <i>verificerbare fragmenter,<\/i>det vil sige, at folk frit kan pr\u00e6sentere falske fragmenter og hindre genoprettelsen af den korrekte hemmelighed. En fjendtlig fragmentopbevarer med tilstr\u00e6kkelig information kan endda producere et andet fragment ved at \u00e6ndre <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/8f646ae3193da8c9be778eceb315e902.jpg\" style=\"display:block;margin: 0 auto;\" \/> som han \u00f8nsker. Dette problem l\u00f8ses ved hj\u00e6lp af <i>verificerbare hemmelighedsdeleskemaer,<\/i>s\u00e5som Feldman's skema.<\/p>\n<p>Et andet problem er, at l\u00e6ngden af ethvert fragment er lig med l\u00e6ngden af den tilsvarende hemmelighed, s\u00e5 l\u00e6ngden af hemmeligheden kan nemt bestemmes. Dette problem l\u00f8ses ved triviel <i>fyldning<\/i> af hemmeligheden med tilf\u00e6ldige tal op til en fast l\u00e6ngde.<\/p>\n<p>Endelig er det vigtigt at bem\u00e6rke, at vores bekymringer om sikkerhed kan g\u00e5 ud over selve skemaet. For rigtig kryptografiske applikationer er der ofte trusler fra sidekanaler, hvor angriberen fors\u00f8ger at udtr\u00e6kke nyttig information fra applikationens k\u00f8rselstid, cache, nedbrud osv. Hvis dette v\u00e6kker bekymring, b\u00f8r der i udviklingsfasen tages n\u00f8je overvejelser om brugen af beskyttelsesforanstaltninger som funktioner og s\u00f8gning med konstant k\u00f8rselstid for at forhindre skrivning af hukommelse til disk og overveje en r\u00e6kke andre ting, der g\u00e5r ud over denne artikel.<\/p>\n<h1>Demo<\/h1>\n<p>\nP\u00e5 <noindex><a rel=\"nofollow\" href=\"https:\/\/ericrafaloff.com\/shamirs-secret-sharing-scheme\/\">denne side<\/a><\/noindex> har en interaktiv demonstration af Shamir's hemmelighedsdeleskema. Demonstrationen er bygget p\u00e5 biblioteket <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/gburca\/ssss-js\/\">ssss-js<\/a><\/noindex>, som i sig selv er en JavaScript-port af det popul\u00e6re program <noindex><a rel=\"nofollow\" href=\"http:\/\/point-at-infinity.org\/ssss\/\">ssss<\/a><\/noindex>. Bem\u00e6rk, at beregningen af store v\u00e6rdier <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/4d8ec4bf92d337e22ed38aef8c2afa60.jpg\" style=\"display:block;margin: 0 auto;\" \/>, <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/cadfa859ca9627c9c3d63d52e1270de2.jpg\" style=\"display:block;margin: 0 auto;\" \/> og <img decoding=\"async\" alt=\"Shamir&#039;s Secret Sharing Scheme\" src=\"\/wp-content\/uploads\/2019\/12\/c66b23e0128c4b7a50e9d8b0ed99e406.jpg\" style=\"display:block;margin: 0 auto;\" \/> kan tage noget tid.<br \/>\n<br \/>Kilde: <a content=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/habr.com\/ru\/post\/431392\/\">habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0420\u0430\u0441\u0441\u043c\u043e\u0442\u0440\u0438\u043c \u0441\u0446\u0435\u043d\u0430\u0440\u0438\u0439, \u043a\u043e\u0433\u0434\u0430 \u043d\u0435\u043e\u0431\u0445\u043e\u0434\u0438\u043c\u043e \u043e\u0431\u0435\u0441\u043f\u0435\u0447\u0438\u0442\u044c \u0431\u0435\u0437\u043e\u043f\u0430\u0441\u043d\u043e\u0441\u0442\u044c \u0431\u0430\u043d\u043a\u043e\u0432\u0441\u043a\u043e\u0433\u043e \u0445\u0440\u0430\u043d\u0438\u043b\u0438\u0449\u0430. \u041e\u043d\u043e \u0441\u0447\u0438\u0442\u0430\u0435\u0442\u0441\u044f \u0430\u0431\u0441\u043e\u043b\u044e\u0442\u043d\u043e \u043d\u0435\u043f\u0440\u0438\u0441\u0442\u0443\u043f\u043d\u044b\u043c \u0431\u0435\u0437 \u043a\u043b\u044e\u0447\u0430, \u043a\u043e\u0442\u043e\u0440\u044b\u0439 \u0432\u0430\u043c \u0432\u044b\u0434\u0430\u044e\u0442 \u0432 \u043f\u0435\u0440\u0432\u044b\u0439 \u0436\u0435 \u0434\u0435\u043d\u044c \u0440\u0430\u0431\u043e\u0442\u044b. \u0412\u0430\u0448\u0430 \u0446\u0435\u043b\u044c\u00a0\u2014 \u043d\u0430\u0434\u0451\u0436\u043d\u043e \u0441\u043e\u0445\u0440\u0430\u043d\u0438\u0442\u044c \u043a\u043b\u044e\u0447. \u041f\u0440\u0435\u0434\u043f\u043e\u043b\u043e\u0436\u0438\u043c, \u0432\u044b \u0440\u0435\u0448\u0438\u043b\u0438 \u0432\u0441\u0451 \u0432\u0440\u0435\u043c\u044f \u0445\u0440\u0430\u043d\u0438\u0442\u044c \u043a\u043b\u044e\u0447 \u043f\u0440\u0438 \u0441\u0435\u0431\u0435, \u043f\u0440\u0435\u0434\u043e\u0441\u0442\u0430\u0432\u043b\u044f\u044f \u0434\u043e\u0441\u0442\u0443\u043f \u043a \u0445\u0440\u0430\u043d\u0438\u043b\u0438\u0449\u0443 \u043f\u043e \u043c\u0435\u0440\u0435 \u043d\u0435\u043e\u0431\u0445\u043e\u0434\u0438\u043c\u043e\u0441\u0442\u0438. \u041d\u043e \u0432\u044b \u0431\u044b\u0441\u0442\u0440\u043e \u043f\u043e\u0439\u043c\u0451\u0442\u0435, \u0447\u0442\u043e \u0442\u0430\u043a\u043e\u0435 \u0440\u0435\u0448\u0435\u043d\u0438\u0435 \u043d\u0430 \u043f\u0440\u0430\u043a\u0442\u0438\u043a\u0435 \u043d\u043e\u0440\u043c\u0430\u043b\u044c\u043d\u043e \u043d\u0435 \u043c\u0430\u0441\u0448\u0442\u0430\u0431\u0438\u0440\u0443\u0435\u0442\u0441\u044f, [&hellip;]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[688],"tags":[],"class_list":["post-53444","post","type-post","status-publish","format-standard","hentry","category-administrirovanie"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.3 - 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