{"id":111506,"date":"2023-11-14T21:10:14","date_gmt":"2023-11-14T19:10:14","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/vossozdanie-rsa-klyuchej-cherez-analiz-ssh-soedinenij-k-sbojnym-serveram"},"modified":"2023-11-14T21:10:14","modified_gmt":"2023-11-14T19:10:14","slug":"vossozdanie-rsa-klyuchej-cherez-analiz-ssh-soedinenij-k-sbojnym-serveram","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/news\/vossozdanie-rsa-klyuchej-cherez-analiz-ssh-soedinenij-k-sbojnym-serveram","title":{"rendered":"Recria\u00e7\u00e3o de chaves RSA atrav\u00e9s da an\u00e1lise de conex\u00f5es SSH a servidores com falha","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Um grupo de pesquisadores da Universidade da Calif\u00f3rnia em San Diego demonstrou a possibilidade de recriar chaves RSA privadas de servidores SSH, utilizando a an\u00e1lise passiva do tr\u00e1fego SSH. O ataque pode ser realizado em servidores onde, devido a circunst\u00e2ncias ou a\u00e7\u00f5es de um atacante, ocorrem falhas durante o c\u00e1lculo da assinatura digital ao estabelecer uma conex\u00e3o SSH. As falhas podem ser tanto de software (execu\u00e7\u00e3o incorreta de opera\u00e7\u00f5es matem\u00e1ticas, corrup\u00e7\u00e3o de mem\u00f3ria), quanto de hardware (erros no funcionamento da NVRAM e DRAM ou falhas devido a interrup\u00e7\u00f5es de energia). <\/p>\n

Uma das op\u00e7\u00f5es para induzir falhas pode ser ataques da classe RowHammer, que permitem, entre outras coisas, distorcer o conte\u00fado de bits de mem\u00f3ria espec\u00edficos por meio de leituras c\u00edclicas intensivas de dados em c\u00e9lulas de mem\u00f3ria adjacentes, seja remotamente ou ao processar c\u00f3digo JavaScript no navegador. Outra alternativa para provocar falhas pode ser a explora\u00e7\u00e3o de vulnerabilidades que levam a estouros de buffer e corrup\u00e7\u00e3o de dados com chaves na mem\u00f3ria. <\/p>\n

O estudo publicado mostra que, ao usar assinaturas digitais em SSH baseadas no algoritmo RSA, ataques para recriar chaves privadas RSA usando o m\u00e9todo Lattice (Fault Attack) s\u00e3o aplic\u00e1veis nas ocorr\u00eancias de falhas de software ou hardware durante o processo de c\u00e1lculo da assinatura. A ess\u00eancia do m\u00e9todo \u00e9 que, comparando assinaturas digitais RSA corretas e falhadas, \u00e9 poss\u00edvel determinar o maior divisor comum para um dos n\u00fameros primos usados na forma\u00e7\u00e3o da chave. <\/p>\n

A criptografia RSA baseia-se na opera\u00e7\u00e3o de exponencia\u00e7\u00e3o modular de um grande n\u00famero. A chave p\u00fablica cont\u00e9m o m\u00f3dulo e o expoente. O m\u00f3dulo \u00e9 formado a partir de dois n\u00fameros primos aleat\u00f3rios, que s\u00e3o conhecidos apenas pelo propriet\u00e1rio da chave privada. O ataque pode ser aplicado a implementa\u00e7\u00f5es de RSA que utilizam o Teorema Chin\u00eas dos Restos e esquemas de preenchimento determinado, como PKCS#1 v1.5. <\/p>\n

Para realizar um ataque, \u00e9 suficiente o monitoramento passivo de conex\u00f5es leg\u00edtimas a um servidor SSH at\u00e9 identificar, no tr\u00e1fego, uma assinatura digital comprometida, que pode ser usada como fonte de informa\u00e7\u00e3o para recriar a chave RSA privada. Ap\u00f3s a recria\u00e7\u00e3o da chave RSA do host, o atacante pode, durante um ataque MITM, redirecionar silenciosamente os pedidos para um host falso que se passa por um servidor SSH comprometido e interceptar os dados transmitidos para este. servidor<\/a> de dados. <\/p>\n

Como resultado do estudo de uma cole\u00e7\u00e3o de dados de rede interceptados, incluindo aproximadamente 5,2 bilh\u00f5es de registros relacionados ao uso do protocolo SSH, os pesquisadores identificaram cerca de 3,2 bilh\u00f5es de chaves de host abertas e assinaturas digitais utilizadas durante a negocia\u00e7\u00e3o da sess\u00e3o SSH. Destas, 1,2 bilh\u00e3o (39,1%) foram geradas usando o algoritmo RSA. Em 593.671 casos (0,048%), a assinatura RSA estava corrompida e n\u00e3o passava na verifica\u00e7\u00e3o. Para 4.962 assinaturas corrompidas, foi poss\u00edvel aplicar o m\u00e9todo de fatoriza\u00e7\u00e3o de Lattice para determinar a chave privada a partir da chave p\u00fablica conhecida, o que permitiu, em \u00faltima an\u00e1lise, recriar 189 pares \u00fanicos de chaves RSA (em muitos casos, as mesmas chaves e dispositivos falhos foram usados para gerar diferentes assinaturas comprometidas). A recria\u00e7\u00e3o das chaves levou cerca de 26 horas de tempo de processamento.

\"Recria\u00e7\u00e3o<\/center> <\/p>\n

O problema afeta apenas implementa\u00e7\u00f5es espec\u00edficas do protocolo SSH, utilizadas principalmente em dispositivos embarcados. Como exemplos de dispositivos com implementa\u00e7\u00f5es problem\u00e1ticas do SSH, foram mencionados produtos da Zyxel, Cisco, Mocana e Hillstone Networks. O OpenSSH n\u00e3o est\u00e1 sujeito ao problema, pois utiliza a biblioteca OpenSSL (ou LibreSSL) para gerar chaves, na qual a prote\u00e7\u00e3o contra ataques baseados em an\u00e1lise de falhas (Fault Attack) existe desde 2001. Al\u00e9m disso, no OpenSSH, o esquema de assinaturas digitais ssh-rsa (baseado em sha1) foi declarado obsoleto e desativado na vers\u00e3o 8.8 em 2020 (o suporte para os esquemas rsa-sha2-256 e rsa-sha2-512 continua). O ataque pode potencialmente ser aplic\u00e1vel tamb\u00e9m ao protocolo IPsec, mas os pesquisadores n\u00e3o tiveram dados experimentais suficientes para confirmar tal ataque na pr\u00e1tica.
\n
Fonte: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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