'''Logjam''' is a [[Vulnerability_(computing)|security exploitvulnerability]] against [[export of cryptography from the United States|US export-grade]] 512-bit keys in [[Diffie–Hellman key exchange]]. cryptographicIt algorithmwas discovered by a group of computer scientists and publicly reported on May 20, 2015.<ref>{{cite web |url=https://weakdh.org |title=The Logjam Attack |website=weakdh.org |date=2015-05-20}}</ref><ref>{{cite web |url=http://arstechnica.com/security/2015/05/https-crippling-attack-threatens-tens-of-thousands-of-web-and-mail-servers/ |title=HTTPS-crippling attack threatens tens of thousands of Web and mail servers |author=Dan Goodin |publisher=[[Ars Technica]] |date=2015-05-20}}</ref><ref>{{cite web |url=http://phoronixwww.zdnet.com/scan.php?page=news_item&px=HTTPSarticle/logjam-Logjamsecurity-Vulnerabilityflaw-leaves-tens-of-thousands-of-https-websites-vulnerable/ |title=AnotherLogjam HTTPSsecurity Vulnerabilityflaw Rattlesleaves Thetop InternetHTTPS websites, mail servers vulnerable|author=EricCharlie GriffithOsborne |publisher=[[PhoronixZDNet]] |date=2015-05-20}}</ref>. The vulnerability allows a man-in-the-middle network attacker to downgrade a TLS connection to use 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>D. Adrian, K. Bhargavan, Z. Durumeric, P. Gaudry, M. Green, J. A. Halderman, N. Heninger, D. Springall, E. Thomé, L. Valenta, B. VanderSloot, E. Wustrow, S. Zanella-Béguelin, P. Zimmermann</ref>
