This security update resolves a vulnerability in Microsoft Windows that facilitates exploitation of the publicly disclosed Logjam technique, an industry-wide issue that is not specific to Windows operating systems. The vulnerability could allow information disclosure when Secure Channel (Schannel) allows the use of a weak Diffie-Hellman ephemeral (DHE) key length of 512 bits in an encrypted TLS session. Allowing 512-bit DHE keys makes DHE key exchanges weak and vulnerable to various attacks.