{"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\/pt\/blog\/news\/predstavlen-bolee-effektivnyj-metod-opredeleniya-prefiksov-kollizij-dlya-sha-1","title":{"rendered":"Apresentado um m\u00e9todo mais eficiente para determinar prefixos de colis\u00f5es para SHA-1","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Pesquisadores do Instituto Nacional de Pesquisa em Inform\u00e1tica e Automa\u00e7\u00e3o da Fran\u00e7a (INRIA) e da Universidade Tecnol\u00f3gica de Nanyang (Cingapura) desenvolveram<\/a><\/noindex> um algoritmo avan\u00e7ado o m\u00e9todo<\/a><\/noindex> ataques<\/a><\/noindex> baseado no SHA-1, que simplifica significativamente a cria\u00e7\u00e3o de dois documentos diferentes com os mesmos hashes SHA-1. A ess\u00eancia do m\u00e9todo \u00e9 reduzir a opera\u00e7\u00e3o de busca completa por colis\u00f5es no SHA-1 a um ataque de colis\u00e3o com um prefixo especificado<\/a><\/noindex>, onde uma colis\u00e3o ocorre com determinados prefixos, independentemente dos outros dados no conjunto. Em outras palavras, \u00e9 poss\u00edvel calcular dois prefixos predefinidos e, se um for anexado a um documento e o outro ao segundo \u2014 os hashes SHA-1 resultantes para esses arquivos ser\u00e3o iguais.<\/p>\n

Esse tipo de ataque ainda requer enormes c\u00e1lculos e a busca por prefixos continua mais complexa do que a busca por colis\u00f5es comum, mas a efic\u00e1cia pr\u00e1tica do resultado \u00e9 consideravelmente maior. Se at\u00e9 agora o m\u00e9todo mais r\u00e1pido para encontrar prefixos de colis\u00e3o no SHA-1 exigia realizar 277,1 opera\u00e7\u00f5es, o novo m\u00e9todo reduz o n\u00famero de c\u00e1lculos para a faixa de 266,9 a 269,4. Com esse n\u00edvel de c\u00e1lculos, o custo estimado do ataque \u00e9 de menos de cem mil d\u00f3lares, o que \u00e9 acess\u00edvel para servi\u00e7os de seguran\u00e7a e grandes corpora\u00e7\u00f5es. Para compara\u00e7\u00e3o, a busca por uma colis\u00e3o comum requer cerca de 264,7 opera\u00e7\u00f5es.<\/p>\n

Em artigo anterior, eu fiz uma an\u00e1lise das possibilidades do iOS para a composi\u00e7\u00e3o musical, e o tema de hoje \u00e9<\/a><\/noindex> demonstra\u00e7\u00f5es<\/a><\/noindex> da Google sobre a capacidade de gerar diferentes arquivos PDF com o mesmo hash SHA-1 foi utilizada<\/a><\/noindex> uma t\u00e9cnica de combinar dois documentos em um s\u00f3 arquivo, alternando a camada vis\u00edvel e deslocando a etiqueta de sele\u00e7\u00e3o da camada para a \u00e1rea onde a colis\u00e3o ocorre. Com custos de recursos semelhantes (para encontrar a primeira colis\u00e3o SHA-1, a Google gastou um ano de c\u00e1lculos em um cluster de 110 GPUs), o novo m\u00e9todo permite alcan\u00e7ar uma correspond\u00eancia de SHA-1 para dois conjuntos de dados arbitr\u00e1rios. Do ponto de vista pr\u00e1tico, \u00e9 poss\u00edvel preparar certificados TLS que mencionam dom\u00ednios diferentes, mas possuem hashes SHA-1 id\u00eanticos. Essa capacidade permite que uma Autoridade Certificadora mal-intencionada crie um certificado para uma assinatura digital que pode ser usada para autorizar certificados falsos para dom\u00ednios arbitr\u00e1rios. O problema tamb\u00e9m pode ser usado para comprometer protocolos que dependem da aus\u00eancia de colis\u00f5es, como TLS, SSH e IPsec.<\/p>\n

A estrat\u00e9gia proposta para a busca de prefixos para colis\u00f5es envolve a divis\u00e3o dos c\u00e1lculos em duas etapas. Na primeira etapa, realiza-se a busca de blocos que est\u00e3o na borda da colis\u00e3o, inserindo vari\u00e1veis aleat\u00f3rias em cadeias em um conjunto alvo pr\u00e9-definido de diferen\u00e7as. Na segunda etapa, em n\u00edvel de blocos individuais, as cadeias de diferen\u00e7as obtidas s\u00e3o comparadas com pares de estados que levam a colis\u00f5es, utilizando m\u00e9todos de ataques tradicionais de busca de colis\u00f5es. <\/p>\n

Embora a possibilidade te\u00f3rica de um ataque ao SHA-1 tenha sido comprovada em 2005, e na pr\u00e1tica a primeira colis\u00e3o foi encontrada<\/a><\/noindex> em 2017, o SHA-1 ainda est\u00e1 em uso e \u00e9 coberto por alguns padr\u00f5es e tecnologias (TLS 1.2, Git, etc.). O principal objetivo do trabalho realizado foi fornecer mais um argumento convincente para a imediata descontinua\u00e7\u00e3o do uso do SHA-1, especialmente em certificados e assinaturas digitais.<\/p>\n

Adicionalmente, pode-se destacar publica\u00e7\u00e3o<\/a><\/noindex> resultados<\/noindex> de criptoan\u00e1lise de cifradores SIMON-32\/64<\/a><\/noindex>, desenvolvidos pela NSA dos EUA e aprovados em 2018 como padr\u00e3o ISO\/IEC 29167-21:2018<\/a><\/noindex>.
\nOs pesquisadores conseguiram desenvolver um m\u00e9todo de recupera\u00e7\u00e3o da chave secreta baseado em dois pares conhecidos de texto plano e texto criptografado. Com recursos computacionais limitados, a busca pela chave pode levar de v\u00e1rias horas a v\u00e1rios dias. A taxa de sucesso te\u00f3rica do ataque \u00e9 estimada em 0,25, enquanto a pr\u00e1tica para o prot\u00f3tipo existente \u00e9 de 0,025.<\/p>\n

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

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

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