Logjam (computer security): Difference between revisions

Revision as of 17:07, 16 October 2015

Revision as of 17:08, 16 October 2015

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One vulnerability demonstrated by the authors was using a man-in-the-middle network attacker to downgrade a [[Transport Layer Security]] (TLS) connection to use 512 bit DH export-grade cryptography, allowing him to read the exchanged data and inject data into the connection. It affects the [[HTTPS]], [[SMTPS]], and [[IMAPS]] protocols, among others.<ref>{{cite web |last1=Adrian |first1=David |last2=Bhargavan |first2=Karthikeyan |last3=Durumeric |first3=Zakir |last4=Gaudry |first4=Pierrick |last5=Green |first5=Matthew |last6=Halderman |first6=J. Alex |last7=Heninger |first7=Nadia |last8=Springall |first8=Drew |last9=Thomé |first9=Emmanuel |last10=Valenta |first10=Luke |last11=VanderSloot |first11=Benjamin |last12=Wustrow |first12=Eric |last13=Zanella-Béguelin |first13=Santiago |last14=Zimmermann |first14=Paul |title=Imperfect Forward Secrecy: How Diffie-Hellman Fails in Practice |url=https://weakdh.org/imperfect-forward-secrecy.pdf |date=October 2015}}</ref> Its CVE ID is CVE-2015-4000.<ref>https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-4000</ref>

The authors also estimated the feasibility of the attack against 1024 bit Diffie–Hellman primes. By design, many Diffie–Hellman implementations use the same pregenerated prime for their field. This was considered secure, since the [[discrete log problem]] is still considerconsidered hard even if the fieldgroup is known and reused. The researchers calculated the cost of creating logjam precomputation for one 1024-bit prime at hundreds of millions of USD, and noted that this was well within range of the FY2012 $10.5 billion U.S. Consolidated Cryptologic Program (which includes NSA). Because of the reuse of primes, generating precomputation for just one prime would break two-thirds of VPNs and a quarter of all SSH servers globally. The researchers noted that this attack fits claims in leaked NSA papers that NSA is able to break much current crypto.<ref name="paper" />

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