Logjam is a security vulnerability in systems that use Diffie–Hellman key exchange with the same prime number. It was discovered by a team of computer scientists and publicly reported on May 20, 2015.[1] The discoverers were able to demonstrate their attack on 512-bit (US export-grade) DH systems. They estimated that a state-level attacker could do so for 1024-bit systems, then widely used, thereby allowing decryption of a significant fraction of Internet traffic. They recommended upgrading to at least 2048 bits for shared prime systems.[2][3][4]