{"id":33517,"date":"2019-10-31T21:53:04","date_gmt":"2019-10-31T18:53:04","guid":{"rendered":"https:\/\/prohoster.info\/blog\/predstavlen-bolee-effektivnyj-metod-opredeleniya-prefiksov-kollizij-dlya-sha-1\/"},"modified":"2019-10-31T21:53:04","modified_gmt":"2019-10-31T18:53:04","slug":"predstavlen-bolee-effektivnyj-metod-opredeleniya-prefiksov-kollizij-dlya-sha-1","status":"publish","type":"post","link":"https:\/\/prohoster.info\/ro\/blog\/news\/predstavlen-bolee-effektivnyj-metod-opredeleniya-prefiksov-kollizij-dlya-sha-1","title":{"rendered":"A fost introdus\u0103 o metod\u0103 mai eficient\u0103 pentru determinarea prefixelor coliziunilor pentru SHA-1.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Cercet\u0103torii de la Institutul Na\u021bional de Cercetare \u00een Informatic\u0103 \u0219i Automatizare (INRIA) din Fran\u021ba \u0219i de la Universitatea Tehnologic\u0103 Nanyang (Singapore) au dezvoltat<\/a><\/noindex> un algoritm \u00eembun\u0103t\u0103\u021bit metoda<\/a><\/noindex> atacuri<\/a><\/noindex> \u00eempotriva algoritmului SHA-1, care simplific\u0103 semnificativ crearea a dou\u0103 documente diferite cu acelea\u0219i hash-uri SHA-1. Esen\u021ba metodei const\u0103 \u00een reducerea opera\u021biei de generare complet\u0103 a coliziunilor \u00een SHA-1 la atacul de coliziune cu prefix specificat<\/a><\/noindex>, la care coliziunea apare \u00een prezen\u021ba unor prefixe specifice, indiferent de celelalte date din set. Cu alte cuvinte, se pot calcula dou\u0103 prefixe predeterminate, iar dac\u0103 unul este ata\u0219at unui document, iar cel\u0103lalt altui document \u2014 hash-urile SHA-1 rezultante pentru aceste fi\u0219iere vor fi identice.<\/p>\n

Aceast\u0103 form\u0103 de atac necesit\u0103 \u00een continuare calcule uria\u0219e, iar generarea prefixelor r\u0103m\u00e2ne mai complex\u0103 dec\u00e2t generarea obi\u0219nuit\u0103 a coliziunilor, dar eficien\u021ba practic\u0103 a rezultatului este semnificativ mai ridicat\u0103. Dac\u0103 p\u00e2n\u0103 acum cea mai rapid\u0103 metod\u0103 de c\u0103utare a prefixelor de coliziune \u00een SHA-1 necesita realizarea a 277.1 opera\u021bii, noua metod\u0103 reduce num\u0103rul de calcule la un interval de la 266.9 la 269.4. La un astfel de nivel de calcule, costul estimat al atacului este de sub o sut\u0103 de mii de dolari, ceea ce este destul de accesibil pentru serviciile secrete \u0219i corpora\u021biile mari. Ca termen de compara\u021bie, c\u0103utarea unei coliziuni obi\u0219nuite necesit\u0103 executarea a aproximativ 264.7 opera\u021bii.<\/p>\n

\u00cen anterior<\/a><\/noindex> demonstra\u021bii<\/a><\/noindex> Google a capacit\u0103\u021bii de a genera diferite fi\u0219iere PDF cu acela\u0219i hash SHA-1 a fost utilizat\u0103<\/a><\/noindex> o metod\u0103 de combinare \u00eentr-un singur fi\u0219ier a dou\u0103 documente, prin comutarea stratului vizibil \u0219i mutarea m\u0103rcii de selec\u021bie a stratului \u00een zona de apari\u021bie a coliziunii. Cu costuri de resurse apropiate (Google a cheltuit un an de calcule pe un cluster de 110 GPU-uri pentru a g\u0103si prima coliziune SHA-1), noua metod\u0103 permite atingerea unui coincid cu SHA-1 pentru dou\u0103 seturi de date arbitrare. Din punct de vedere practic, este posibil s\u0103 se preg\u0103teasc\u0103 certificate TLS \u00een care sunt men\u021bionate domenii diferite, dar care au hash-uri SHA-1 identice. Aceast\u0103 capacitate permite unui centru de certificare r\u0103u inten\u021bionat s\u0103 creeze un certificat pentru o semn\u0103tur\u0103 digital\u0103 care poate fi utilizat\u0103 pentru a autoriza certificate fictive pentru domenii arbitrare. Problema poate fi folosit\u0103 \u0219i pentru compromiterea protocoalelor care se bazeaz\u0103 pe absen\u021ba coliziunilor, cum ar fi TLS, SSH \u0219i IPsec.<\/p>\n

Strategia propus\u0103 pentru c\u0103utarea prefixelor de coliziune implic\u0103 \u00eemp\u0103r\u021birea calculelor \u00een dou\u0103 etape. \u00cen prima etap\u0103, se caut\u0103 blocuri care sunt pe punctul de a colida, prin \u00eencorporarea variabilelor aleatorii ale lan\u021burilor \u00eentr-un set \u021bint\u0103 predefinit de diferen\u021be. \u00cen a doua etap\u0103, la nivelul blocurilor individuale, lan\u021burile de diferen\u021be ob\u021binute sunt comparate cu perechile de st\u0103ri care duc la coliziuni, folosind metodele atacurilor tradi\u021bionale pentru c\u0103utarea coliziunilor. <\/p>\n

De\u0219i posibilitatea teoretic\u0103 de atac asupra SHA-1 a fost demonstrat\u0103 \u00eenc\u0103 din 2005, iar prima coliziune \u00een practic\u0103 a fost realizat\u0103<\/a><\/noindex> \u00een 2017, SHA-1 este \u00eenc\u0103 \u00een circula\u021bie \u0219i este inclus \u00een anumite standarde \u0219i tehnologii (TLS 1.2, Git etc.). Principala \u021bint\u0103 a lucr\u0103rii a fost dorin\u021ba de a oferi un alt argument puternic pentru \u00eencetarea imediat\u0103 a utiliz\u0103rii SHA-1, \u00een special \u00een certificatele \u0219i semn\u0103turile digitale.<\/p>\n

apari\u021bia publicarea<\/a><\/noindex> rezultatelor<\/noindex> cryptoanalizei \u0219ifrelor pe blocuri SIMON-32\/64<\/a><\/noindex>, dezvoltate de NSA SUA \u0219i aprobate \u00een 2018 ca standard ISO\/IEC 29167-21:2018<\/a><\/noindex>.
\nCercet\u0103torii au reu\u0219it s\u0103 dezvolte o metod\u0103 de recuperare a cheii private bazat\u0103 pe dou\u0103 perechi cunoscute din text deschis \u0219i text criptat. Cu resurse de calcul limitate, descoperirea cheii poate dura de la c\u00e2teva ore la c\u00e2teva zile. Coeficientul teoretic de succes al atacului este estimat la 0.25, iar cel practic pentru prototipul existent \u2014 0.025.<\/p>\n

<\/a><\/noindex><\/p>\n

Sursa: opennet.ro<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0418\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u0438 \u0438\u0437 \u0444\u0440\u0430\u043d\u0446\u0443\u0437\u0441\u043a\u043e\u0433\u043e \u0433\u043e\u0441\u0443\u0434\u0430\u0440\u0441\u0442\u0432\u0435\u043d\u043d\u043e\u0433\u043e \u0438\u043d\u0441\u0442\u0438\u0442\u0443\u0442\u0430 \u0438\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u043d\u0438\u0439 \u0432 \u0438\u043d\u0444\u043e\u0440\u043c\u0430\u0442\u0438\u043a\u0435 \u0438 \u0430\u0432\u0442\u043e\u043c\u0430\u0442\u0438\u043a\u0435 (INRIA) \u0438 \u041d\u0430\u043d\u044c\u044f\u043d\u0441\u043a\u043e\u0433\u043e \u0442\u0435\u0445\u043d\u043e\u043b\u043e\u0433\u0438\u0447\u0435\u0441\u043a\u043e\u0433\u043e \u0443\u043d\u0438\u0432\u0435\u0440\u0441\u0438\u0442\u0435\u0442\u0430 (\u0421\u0438\u043d\u0433\u0430\u043f\u0443\u0440) \u0440\u0430\u0437\u0440\u0430\u0431\u043e\u0442\u0430\u043b\u0438 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