{"id":54924,"date":"2020-01-08T00:00:00","date_gmt":"2020-01-07T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/predlozhen-metod-opredeleniya-kollizij-v-sha-1-prigodnyj-dlya-ataki-na-pgp"},"modified":"2020-02-18T14:02:59","modified_gmt":"2020-02-18T11:02:59","slug":"predlozhen-metod-opredeleniya-kollizij-v-sha-1-prigodnyj-dlya-ataki-na-pgp","status":"publish","type":"post","link":"https:\/\/prohoster.info\/ro\/blog\/news\/predlozhen-metod-opredeleniya-kollizij-v-sha-1-prigodnyj-dlya-ataki-na-pgp","title":{"rendered":"Metoda propus\u0103 pentru determinarea coliziunilor \u00een SHA-1, adecvat\u0103 pentru atacuri asupra PGP","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Cercet\u0103torii de la Institutul de Cercetare \u00een Informatic\u0103 \u0219i Automatizare din Fran\u021ba (INRIA) \u0219i Universitatea Tehnologic\u0103 Nanyang (Singapore) au prezentat o metod\u0103 de atac Shambles<\/a><\/noindex> (PDF<\/a><\/noindex>), considerat\u0103 prima implementare practic\u0103 a unui atac asupra algoritmului SHA-1, care poate fi utilizat\u0103 pentru a crea semn\u0103turi digitale false PGP \u0219i GnuPG. Cercet\u0103torii cred c\u0103 toate atacurile practice asupra MD5 pot fi aplicate \u0219i asupra SHA-1, de\u0219i \u00een continuare necesit\u0103 resurse considerabile pentru a fi realizate.<\/p>\n

Metoda se bazeaz\u0103 pe efectuarea unui atac de coliziune cu prefix dat<\/a><\/noindex>, care permite pentru dou\u0103 seturi de date arbitrare s\u0103 se potriveasc\u0103 suplimente, la ata\u0219area c\u0103rora se vor ob\u021bine seturi care provoac\u0103 coliziuni, aplicarea algoritmului SHA-1 for fi rezultatul unui hash identic. Cu alte cuvinte, pentru dou\u0103 documente existente se pot calcula dou\u0103 suplimente, iar dac\u0103 unul se ata\u0219eaz\u0103 primului document, iar cel\u0103lalt celui de-al doilea \u2014 hash-urile SHA-1 rezultate pentru aceste fi\u0219iere vor fi identice.<\/p>\n

Noua metod\u0103 se deosebe\u0219te de tehnicile similare propuse anterior prin cre\u0219terea eficien\u021bei c\u0103ut\u0103rii coliziunilor \u0219i demonstrarea aplic\u0103rii practice pentru atacuri asupra PGP. \u00cen special, cercet\u0103torii au reu\u0219it s\u0103 creeze dou\u0103 chei PGP publice de dimensiuni diferite (RSA-8192 \u0219i RSA-6144), cu identificatori de utilizator diferi\u021bi \u0219i cu certificate care genereaz\u0103 coliziuni SHA-1. Prima cheie<\/a><\/noindex> a inclus identificatorul victimei, iar a doua cheie<\/a><\/noindex> a inclus numele \u0219i imaginea atacatorului. Astfel, prin g\u0103sirea coliziunii, certificat identificator al cheilor, care includea cheia \u0219i imaginea atacatorului, avea acela\u0219i hash SHA-1 ca \u0219i certificatul identificator, care includea cheia \u0219i numele victimei. <\/p>\n

Atacatorul putea solicita o semn\u0103tur\u0103 digital\u0103 pentru cheia \u0219i imaginea sa \u00eentr-un centru de certificare extern, dup\u0103 care putea transfera semn\u0103tura digital\u0103 pentru cheia victimei. Semn\u0103tura digital\u0103 r\u0103m\u00e2ne valid\u0103 datorit\u0103 coliziunii \u0219i certific\u0103rii cheii atacatorului de c\u0103tre centrul de certificare, ceea ce \u00eei permite atacatorului s\u0103 ob\u021bin\u0103 controlul asupra cheii numite dup\u0103 victim\u0103 (deoarece hash-ul SHA-1 pentru ambele chei este identic). \u00cen final, atacatorul poate s\u0103 se prezinte ca victima \u0219i s\u0103 semneze orice document \u00een numele acesteia.<\/p>\n

Atacul r\u0103m\u00e2ne deocamdat\u0103 destul de costisitor, dar deja accesibil serviciilor de informa\u021bii \u0219i marilor corpora\u021bii. Pentru simpla potrivire a coliziunilor utiliz\u00e2nd GPU-ul NVIDIA GTX 970 mai ieftin, costurile s-au ridicat la 11 mii de dolari, iar pentru potrivirea coliziunilor cu un prefix dat \u2014 la 45 de mii de dolari (spre compara\u021bie, \u00een 2012, costurile pentru identificarea coliziunilor \u00een SHA-1 erau estimate la 2 milioane de dolari, iar \u00een 2015 \u2014 700 de mii). Pentru a efectua un atac practic asupra PGP-ului, au fost necesare dou\u0103 luni de calcul, implic\u00e2nd 900 GPU NVIDIA GTX 1060, al c\u0103ror \u00eenchiriere a costat cercet\u0103torii 75 de mii de dolari.<\/p>\n

Metoda propus\u0103 de cercet\u0103tori pentru detectarea coliziunilor este de aproximativ 10 ori mai eficient\u0103 dec\u00e2t realiz\u0103rile anterioare \u2014 nivelul de dificultate al calculului coliziunilor a fost redus la 261.2 opera\u021biuni, \u00een loc de 264.7, iar coliziunile cu un prefix dat la 263.4 opera\u021biuni \u00een loc de 267.1. Cercet\u0103torii recomand\u0103 s\u0103 se treac\u0103 c\u00e2t mai cur\u00e2nd de la SHA-1 la utilizarea SHA-256 sau SHA-3, deoarece \u00een prognoza lor, p\u00e2n\u0103 \u00een 2025, costul efectu\u0103rii unui atac va sc\u0103dea la 10 mii de dolari.<\/p>\n

Dezvoltatorii GnuPG au fost notifica\u021bi despre problem\u0103 pe 1 octombrie (CVE-2019-14855), iar pe 25 noiembrie, \u00een versiunea GnuPG 2.2.18, au luat m\u0103suri pentru a bloca certificatele problematice \u2014 toate semn\u0103turile digitale SHA-1, create dup\u0103 19 ianuarie anul trecut, sunt acum considerate invalide. La CAcert, unul dintre principalele centre de certificare pentru chei PGP, se planific\u0103 trecerea la utilizarea unor func\u021bii hash mai sigure pentru certificarea cheilor. Dezvoltatorii OpenSSL, \u00een r\u0103spuns la informa\u021biile privind noua metod\u0103 de atac, au decis s\u0103 dezactiveze SHA-1 la primul nivel de securitate propus implicit (SHA-1 nu va putea fi utilizat pentru certificate \u0219i semn\u0103turi digitale \u00een timpul negocierii conexiunilor).<\/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) \u043f\u0440\u0435\u0434\u0441\u0442\u0430\u0432\u0438\u043b\u0438 \u043c\u0435\u0442\u043e\u0434 \u0430\u0442\u0430\u043a\u0438 Shambles (PDF), \u043a\u043e\u0442\u043e\u0440\u044b\u0439 \u043f\u0440\u0435\u043f\u043e\u0434\u043d\u043e\u0441\u0438\u0442\u0441\u044f \u043a\u0430\u043a \u043f\u0435\u0440\u0432\u0430\u044f \u043f\u0440\u0430\u043a\u0442\u0438\u0447\u0435\u0441\u043a\u0430\u044f \u0440\u0435\u0430\u043b\u0438\u0437\u0430\u0446\u0438\u044f \u0430\u0442\u0430\u043a\u0438 \u043d\u0430 \u0430\u043b\u0433\u043e\u0440\u0438\u0442\u043c SHA-1, \u043a\u043e\u0442\u043e\u0440\u0443\u044e \u043c\u043e\u0436\u043d\u043e \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u044c \u0434\u043b\u044f \u0441\u043e\u0437\u0434\u0430\u043d\u0438\u044f \u0444\u0438\u043a\u0442\u0438\u0432\u043d\u044b\u0445 \u0446\u0438\u0444\u0440\u043e\u0432\u044b\u0445 \u043f\u043e\u0434\u043f\u0438\u0441\u0435\u0439 PGP \u0438 GnuPG. \u0418\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u0438 \u043f\u043e\u043b\u0430\u0433\u0430\u044e\u0442, \u0447\u0442\u043e \u0442\u0435\u043f\u0435\u043f\u0440\u044c \u0432\u0441\u0435 \u043f\u0440\u0430\u043a\u0442\u0438\u0447\u0435\u0441\u043a\u0438\u0435 \u0430\u0442\u0430\u043a\u0438 \u043d\u0430 MD5 \u043c\u043e\u0433\u0443\u0442 \u043f\u0440\u0438\u043c\u0435\u043d\u044f\u0442\u044c\u0441\u044f \u0438 \u0434\u043b\u044f […]<\/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":[702],"tags":[],"class_list":["post-54924","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47A fost propus o metod\u0103 de determinare a coliziunilor \u00een SHA-1, potrivit\u0103 pentru atacuri asupra PGP | ProHoster","description":"Cercet\u0103torii de la 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